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III. WORKING PAPERS


1. Morphology and Distribution of Calcareous Soils in the Mediterranean and Desert Regions
2. Distribution of Calcareous Soils in the Near East Region, their Reclamation and Land Use Measures and Achievements
3. Morphology, Mechanical Composition and Formation of Highly Calcareous, Lacustrine Soils in Turkey
4. Nutrient Supply and Availability in Calcareous Soils1/
5. Response of Crops Grown on Calcareous Soils to Fertilization
6. Some Physical Properties of Highly Calcareous Soils and their Related Management Practices
7. Soil and Water Management Practices for Calcareous Soils1/
8. Irrigation and Drainage Practices of the Organic Calcareous Soils in the Ghab Project in Syria
9. Reclamation and Management of the Calcareous Soils of Egypt
10. Problems of Regional Interest and Suggested Research Programmes for Calcareous Soils
11. Progress Report on the Regional Applied Research Programme on Land and Water Use in the Near East

1. Morphology and Distribution of Calcareous Soils in the Mediterranean and Desert Regions

by

A. Ruellan
Ecole National Supérieure Agronomique
Rennes Cepex, France

Note: This paper was originally submitted in French. The following English version was presented during the Seminar.
SUMMARY

Three characteristics permit the main types of calcareous soils in the desert, arid and Mediterranean countries to be defined.

1) The development of the Bca horizon. This horizon can be:

a) absent;

b) weakly differentiated; the accumulation is diffuse with, sometimes, some pseudo-mycellium (carbonate content: <40%);

c) moderately differentiated Bca contains diffuse and nodular carbonate; nodules can be soft or hard (carbonate content: <60%);

d) very well differentiated: part of the Bca is an "encroûtement" (encrustation); this encrustation (carbonate content: > 60%) can be:

i) a non-platy encrustation (massive or nodular);

ii) a platy encrustation; there are two types:

- calcareous cruet, overlying a non-platy encrustation
- compact slab, overlying a calcareous crust and a non-platy encrustation;
iii) a laminated encrustation; it is the ribboned pellicule that comes on the top of the platy or non-platy encrustation.
2) The carbonate content, texture and thickness of the A horizon.

3) The colour and structure of the epipedon. The epipedon can be:

a) dark, with fine and stable structure;
b) clear;
c) very clear, with weak and unstable structure.
1.1. Introduction

In countries with Mediterranean, arid and desert climates, soils containing calcium carbonate in one or several of their horizons are frequent.

There are two main reasons for this:

The first is the rocks: in these regions they are frequently calcareous, or simply rich in calcium (for example the basalts).

The second is the climate: the frequent alternation of wet and dry periods and the existence of a long dry season are not favourable to deep leaching of the solutions in the soils.

The denominations and classifications of these soils are very varied. I do not want to discuss this question but only to remind you of the names of these soils in three main classification systems:

- in the French system, the Mediterranean and desert calcareous soils are classified as: "peu évolues" (poorly developed) soils, calcimagnesic soils, isohumic soils or as Mediterranean fersiallitic red or brown soils.

- according to the U.S.A. classification, these soils are xerochrepts (inceptisols) argids or orthids (aridisols), rendolls or xerolls (mollisols), xeralfs (alfisols).

- according to the key of the FAO/Unesco Soil Map of the World, the calcareous soils of the Mediterranean and desert countries can be fluvisols, rendzinas, yermosols, xerosols, castanozems or cambisols.

1.2. Morphology of the Calcareous Profile

Three main horizons can be distinguished from observation and study of the distribution of the carbonates in these soils:

- In the middle part of the soils there is an horizon where the content of calcium carbonate is higher than in those situated above and below. It is an horizon of calcium carbonate accumulation, i.e. a Bca; and in it the carbonate is generally partially visible because it is partially concentrated.

- Above this Bca, the carbonate is less abundant and it can even be absent. Therefore from the carbonate this upper horizon is an A horizon.

- Below is the C horizon, that is the parent material, which can be calcareous or not.

The distribution of the carbonate in these three horizons define what can be called the calcareous profile. This calcareous profile is the most important characteristic of these soils which are, in fact, soils with a differentiated calcareous profile. This is the name given to these soils in this paper and the aim is to give and to recall some data about the characteristics and the distribution of these soils however, without going into discussion of the names and of the classification of these soils.

The Bca horizon of these soils is the most important one and a study of the morphological organization of these soils must be started with the study of the Bca horizons. According to morphology of this horizon, three main types of profile are distinguishable.

- First there are soils with a weak differentiated calcareous profile. In these soils the thickness of the Bca horizon is slight, only 20 to about 50 centimeters; the development is weak, i.e. the content of carbonate in this horizon is not very much higher than in the A and C horizons (only some 10 %). Furthermore, the distribution of carbonate in the Bca horizon is diffuse or occasionally concentrated in some pseudo-mycelium.

The accumulation of the calcium carbonate in this type of Bca is in the form of fine particles. The upper and lower limits of this type of Bca horizon are diffuse and it is frequently difficult to recognize the presence of the horizon in the profile. In general it has a clearer colour than the horizons situated above and below, but sometimes it is necessary to wait the results of the analysis to know the presence of the accumulation.

- Secondly there are soils with a Bca horizon in which the calcium carbonate accumulated, is partially concentrated. Calcium carbonate concentration are present and they can be soft or hard. When they are hard they are called nodules. These soils have a moderately differentiated calcareous profile. The upper and the lower limits of this Bca horizon are generally diffuse. The content of carbonate does not exceed 50 to 60% and the thickness of the horizon can vary from 20 to almost 100 cm.

- The third type of soils has a Bca horizon in which the carbonate form in a part of the horizon is a continuous layer known in French as an "encroûtement calcaire". It is almost equivalent, though not exactly, to the American petrocalcic horizon. The term "encroûtement" can be translated lime crusting or calcareous encrustation. The soils with this type of Bca have a very well differentiated calcareous profile.

There are several types of crusting (encrustation):
(i) Non platy lime crusting with two sub types:
a) characterized by a massive, fairly continuous structure or also by a fine polyhedric structure.

b) marked by a nodular and polyhedric structure; the nodular structure is due to the presence of calcium carbonate nodules. The content of calcium carbonate is generally high, between 50 and 80%.

(ii) Platy structure lime crusting, also with two sub types:
a) "croûte calcaire" known in English as calcareous crust. This crust is usually situated above a non platy lime crusting. This type of Bca horizon has the characteristic of being a clear, very distinct platy, laminar structure. The content of calcium carbonate is generally high: 60 to 90%. However, if the parent material is quartz sand (sand dune, sand stone), the calcareous crust may contain only about 40% carbonate.

b) "dalle compacte" which is translated in English as compact slab. This is the transformation of the calcareous crust into very hard, stone-like, platy elements. If there is a slab it is generally situated on top of a calcareous crust. The slab is usually very rich in carbonate: between 70 and 90%. The colour is salmon pink.

(iii) Very fine laminated pellicule which frequently covers the top of the lime crusting and particularly the top of the platy lime crusting. The French name of "pellicule rubanée" may be translated as ribboned pellicule (thin lime pan). It is always a thin formation of some millimetres to one or two centimetres, is frequently very hard and always rich in carbonate - more than 70%, The colour is white or salmon, sometimes with darker lamellae.
To summarize, the Bca horizon of calcareous soils can be :
- First, a diffuse accumulation with or without pseudo-mycelium; in this case the calcareous profile is weakly differentiated.

- Secondly, the Bca horizon contains soft concentrations or nodules (hard concentrations) throughout the thickness of the horizon or only in part of it; the calcareous profile is moderately differentiated.

- Thirdly, part of the Bca horizon is a lime crusting, the thickness of which varies from 10 cm to more than 2 metres. This calcareous profile is very well differentiated.

The lime crusting can be :
- non platy,
- platy, i.e. a crust usually surmounting a non platy lime crusting,
- a compact slab situated on a crust and on a non platy lime crusting.
In the three oases a ribonned pellicule can cover the top of the Bca horizon.

Two points should be noted. Some calcareous soils have no Bca, no accumulation of carbonate and this occurs in two oases. In the first there is no differentiation in the calcareous profile; the content of carbonate is the same from the top to the base of the soil. This is found in young soils. In the second case the calcareous profile is weakly differentiated and there is a progressive increase in the carbonate content from the top-soil to the parent material.

The second point is that in the semi-arid and humid zones of the Mediterranean regions, soils with no carbonate occur frequently on carbonate rocks; "terra rossa" or certain red Mediterranean soils on hard carbonate rooks, are well known examples of this. However, these soils are not included in the scope of this paper.

1.3. Vertical and Lateral Variations of the Calcareous Profiles

To understand the distribution and genesis of these calcareous soils, it is important to study the vertical and lateral variations of the Bca horizons and the correlations that exist between the different types of accumulation and those that exist between the Bca horizon and the A and C horizons,

1.3.1 In a complete Bca horizon the vertical transition between the different layers of accumulation is gradual. From the base of the soil, there is a gradual transition from a layer with soft concentrations and nodules to the nodular lime crusting, then to the crust and to the slab. Only the ribboned pellicule has a distinct limit.

1.3.2 In a catena of soils, in the lateral modification of the Bca horizon, lateral and progressive transitions between the different types of Bca can frequently be noted. There are progressive changes in a Bca with soft concentrations and nodules to non platy lime crusting, to platy lime crusting, and finally to the compact slab. In this catena, there is a progressive increase in the carbonate content and in the thickness of the Bca horizon, the increase in the carbonate content is more accentuated toward being more and more situated on the top of the Bca. This is one fairly frequently encountered example of lateral transition between non platy and platy lime crusting.

It can be concluded that the different types of Bca horizons are closely associated, vertically and horizontally and that they certainly result from the continuous influence of certain pedogenetic mechanisms. Only the ribboned pellicule is independent of these processes.

1.3.3 The correlations between the A and the Bca horizons and the transition between the two need to be considered. When the Bca is diffuse or has soft concentrations or nodules, the transition between the two horizons is progressive; there is a progressive increase in the calcium carbonate content although it is quite impossible to note definite limits on the profile and on the curve.

The transition between an A and a Bca horizon becomes more and more clearly marked laterally in a catena passing from a moderate differentiated profile towards a more differentiated one, that is towards a lime crusting. In the very well differentiated profiles, the limit between the A and the Bca horizon is always very clear and this limit always corresponds to a rapid and significant increase in the carbonate content.

Regarding the correlations between the carbonate content of the A and Bca horizons, it should be noted that there are no correlations; above a weak and thin Bca or above a very thick calcareous crust with a compact slab, the same A horizon can be found and it can be rich or poor in carbonate and either thin or thick.

These facts concerning the transitions between the two horizons, the very weak correlations between the carbonate contents of the two horizons and certain others demonstrate that the carbonate which accumulates in the Bca has a partly lateral origin, that there is in the soils an important lateral migration of the carbonate. This is confirmed when we study the correlations between the Bca and the C horizon; the transition between the two horizons is always progressive and all kinds of carbonate accumulations can develop in non calcareous and in non calcic parent material; however, the presence of a calcareous or a calcic parent material at the top of the slope is necessary to provide the Ca for the lateral migration.

1.4. Distribution of the Soils

Turning now to the principles governing the distribution in these lands of the different types of calcium carbonate profiles, there are several relevant factors.

1.4.1 An accentuation in the accumulation of carbonate is a function of time. For example, when studying the differentiation of the carbonate profile of soils situated on Quaternary alluvial terraces, it will be found that it increases with the rise from the young and low terraces to the high and old terraces. The following sequence will be found: diffuse accumulation, nodules, lime crusting, and a very hard and thick slab. But, in confirmation of remarks made previously in this paper, the increase in the carbonate accumulation is not accompanied by a decarbonization of the A horizon. There is however a light decarbonization on recent terraces but this does not increase on the older ones.

1.4.2 In the distribution of soils along a slope of a certain age, the differentiation of the Bca increases as the slope descends. The thickness of the A horizon also increases. This is the result first of the lateral migration of the calcium in the soils and secondly of slight surface erosion.

1.4.3 When considering the decarbonization of the A horizon in relation to the parent material and as a result of the climate, two points should be borne in mind.

(i) The decarbonization of the A horizon is more pronounced when the alteration of the parent material is slower or when it is more permeable and, obviously, when the parent material is poorer in carbonate. For example, the decarbonization of the A horizon is more pronounced in soils developed on hard calcareous rocks or on calcareous sandstones, than in soils developed on marls, which are impermeable and subject to rapid alteration and erosion. In such conditions total decarbonization of the A horizon is impossible in Mediterranean and arid countries.

(ii) Passing from the arid to the humid climate, there is a slight augmentation of the decarbonization of the A horizon. This increase is more noticeable on hard or permeable calcareous parent materials, than on marl or alluvions.

1.4.4 The Bca horizon changes very little in relation to the climate. It is worth recording that in young soils, the Bca horizons are better differentiated in the subhumid than in the arid regions and that in old soils, the platy forms of the lime crusting are better developed in the arid and semi-arid countries than in the humid ones. This is because the hard and platy forms of the lime crusting result from consequential and rapid variations in the humidity of soils.

1.4.5 Concerning the relation between the Bca horizon and the parent material, it is important to remember that, because of lateral migration in the soils, calcareous soils can be found on non calcareous rocks and also on non calcic rocks. Furthermore, it is interesting to note the influence of the texture of the parent material; hard nodules and hard forms of lime crusting are particularly favoured by coarse texture.

The foregoing remarks can be considered as a summary of the essential points concerning the morphology and distribution of calcareous soils in Mediterranean, arid and desert regions.

The calcium carbonate profile is, of course, not the only important feature of these calcareous soils. It is also necessary to study: the textural profile, the structural profile, the colours, the organic profile, the repartition of the iron in the soils, the characteristics of the base exchange complex and of the soil solution, the mineralogy of the clay, etc.

There is a great deal to be said on these subjects but it is beyond the scope of this paper. However, there are some brief facts about texture, structure and colour which should be mentioned.

Main types of Bca Horizon

1.5. Texture. Structure and Colour of the Soils

1.5.1. Concerning texture, it should he remembered that first, because of the presence of carbonates, textural analysis will always be difficult and should be interpretated with caution and secondly, that "B textural" are frequent in these soils, in all regions, humid or desert, but the limits are always diffuse. In soils where the superficial horizon is not calcareous, the "B textural" is above and in the upper part of the Bca, but in soils with calcareous superficial horizons, the Bt is generally less clayey and is situated at the same depth as the Bca horizon.

It seems that, in the majority of the calcareous soils, vertical leaching of the clay is of little importance, the accumulation of clay resulting mainly from alteration. However, if the vertical leaching is not too important, it is not the same for the lateral migration of the clay in the superficial horizon, and the result of this is that the first 10 or 20 centimetres of soil are frequently poor in clay. This phenomena is accentuated by cultivation which destroys organic matter and the structure.

1.5.2. From the colour and the structure of the superficial horizons, it is possible to distinguish three main types of soils.

The first type of soils are those with a dark epipedon equivalent to the mollic epipedon. The value and the chroma of the humid soils are lower than 3.5; the structure of the horizon is well formed, crumbly and granular, very stable. These soils are frequent in the subhumid and semi-arid zones.

The second type of soils are those with a clear epipedon. The value and the chroma of the humid soil are between 3.5 and 4. The structure is more angular, less fine and less stable. These soils are frequent in semi-arid and arid zones.

The third type of soils are those with a very clear epipedon. The value and the chroma are superior to 4. The structure is weak, unstable and on the surface of the soil there is frequently a fine lamellar structure, forming a superficial crust. These soils are frequent in arid and desert countries.

These three types of soils, with dark, clear and very clear epipedon, can be calcareous or non calcareous in the A horizon and they can also have a Bca weakly, moderately or very well differentiated.

Given these three main characteristics; development of the Bca, content of the carbonate in the A horizon and colour and structure of this A horizon, the main types of calcareous soils in desert, arid and Mediterranean countries can be defined.

Two additional remarks should be made about the colour and the structure. The first concerns the red colour of the soils, and particularly the red colour of the superficial horizons; this colour is more accentuated when the carbonate content is weak, the climate is more humid and the parent material is red, which is very frequent.

The second remark concerns the structure of the Bt horizon, which depends on the content of clay, carbonate and organic matter.

1.6. Results of Human Action

In conclusion some remarks must be made on the result of man's action. In these regions when comparing some calcareous soils which have not been cultivated with those that have been cultivated or used for pasture, noticeable differences can be seen at once regarding degradation and decreased fertility of the soils. These differences are typified by:-

considerable diminution of the organic matter;

lightening of the surface colour and degradation of the surface structure with development of a surface crust;

recarbonization of the superficial horizons and lateral leaching of the clay in these superficial horizons; and

conditions highly susceptible to erosion from water and wind.

This degradation has had particularly important consequences and is probably irreversible in the very arid zones. Remaining portions of the natural original vegetation of these zones bear witness that past climatic conditions were more humid than in present times. The equilibrium was delicate and the destruction by man and his domestic animals of the vegetation definately destroyed this delicate ecological balance.

2. Distribution of Calcareous Soils in the Near East Region, their Reclamation and Land Use Measures and Achievements

by

Louay T. Kadry
Regional Soils Specialist
FAO Regional Office, Cairo, ARE

SUMMARY

By virtue of the predominantly semi-arid and arid climate and sedimentary formations that prevail in the majority of the countries in the Near East Region, calcareous soils occur extensively. The following orders have been identified: Calcic xerosols and yermosols, Gypsic xerosols and yermosols, Lithic Cambisols, xerosols and yermosols, Fluvisols, Regosols, Chronic and Haplic Vertisols. Relative progress has been achieved in the investigation, reclamation and utilization of calcareous soils in several countries of the region. To realise effective solutions to the field problems of calcareous soils, it is necessary that a concerted cooperative applied research programme be adopted by the countries of the region. In this programme stress should be directed toward determining soil classification criteria that identify the varying qualities and levels of land and water use potentials.

The discussion emphasised the importance of realizing a consensus by the Seminar on the definition of calcareous soils in terms of their interpretive qualities for land and water use.

2.1. Introduction

Calcareous sediments are a prominent feature of terrains in the Near East Region. Their stratigraphic forms and lithologic constitution can be traced to the prevailing climatic, hydro and biologic environments of the past geologic periods and in particular, the Quaternary and Holocene.

Calcareous soils whose parent material is the calcareous sediments, occur extensively in the Near Bast Region. The characteristics these soils acquire are mainly determined by the climate, parent material, topography and the hydrologic history of the terrain.

The calcareous soils, inspite of their extensive occurrence in all the countries of the Near East Region, their recognition as an intrinsic group of soils has been overshadowed by the other soil quality characteristics with which calcareous soils are closely associated. Saline, saline-alkali (sodic), hydromorphic, sandy, dryland, eroded, etc. soils are a few prominent examples for qualifying this point. Therefore, it is necessary to define calcareous soils in the following context:

"Calcareous soils are those soils with high calcium carbonate content whose physical problems of land and water use for crop production are primarily dominated by the high content of CaCO3, especially the active fraction with high specific surface area".
2.2. Distribution of Calcareous Soils in the Near Bast Region

2.2.1 Kinds of calcareous soils and their general regional distribution

The calcareous soils have many different morphological forms. On the basis of the profile characteristics, the following main kinds are important:

(1) Soils with a calcic horizon; Calciorthids (USDA); Calcic Xerosols and Calcic Yermosols (FAO/Unesco).

These soils have a strong, developed horizon of lime accumulation in the subsoil. The lime is concentrated in the form of concretions or in powdery form. The depth to the horizon usually varies and it is very important in land use. Shallow soils over calcic horizon are damaged by deep cultivation. Developed on Pleistocene alluvial deposits, these soils are quite extensive in Syria, Jordan, Iraq, Iran and Egypt in addition to some areas in other countries.

(2) Soils with petrocalcic horizons; Durorthids (USDA); Calcic Xerosols and Calcic Yermosols (FAO/Unesco).

These soils are like the ones with calcic horizon but the petrocalcic horizon has cemented lime hard pan and they are thus much worse. These soils cover quite extensive areas in southern Saudi Arabia as well as in northern Syria. In Iran and other countries they occupy small areas.

(3) Soils with Gypsic and petrogypsic horizons; Calciorthids (USDA); Gypsic Xerosols and Gypsic Yermosols (FAO/Unesco).

These are calcareous soils with a horizon of gypsum accumulation in the subsoil. The depth to the gypsum horizon determines the land use. These soils are usually not suitable for irrigation. They are very extensive in northern Iraq and eastern Syria.

(4) Shallow soils over limestone or marl; Lithic Camborthids and Lithic Haplorithids (USDA; Lithic Cambisols and Lithic Xerosols and Lithic Yermosols (FAO/Unesco).

Such soils have a shallow root zone underlain by partially weathered rode and then the unweathered rock. Only shallow rooted crops and those crops that can tolerate the lime in the partially weathered rock zone can be grown. These soils occur extensively in southern Lebanon, western Egypt, Iran, Afghanistan, Pakistan and most of the other countries. They occupy steep slopes and have a serious problem of erosion.

(5) Strongly calcareous soils formed in alluvium or loess but without calcic horizon;

Camborthids, Xerorthents and Torriorthents (USDA); Yermosols, Xerosols, Fluvisols and Regosols (FAO/Unesco).

These soils have more than 15 percent calcium carbonate mostly as silt size fraction. As there is no strong zone of lime accumulation, the root zone is quite deep. Such soils have either no profile development or only a weak structural B horizon. Occurring in the arid alluvial plains and the arid mountain valleys, these soils are very extensive, especially in Iraq, central Saudi Arabia, Yemen, Iran, Pakistan, and Afghanistan. Many parts of these soils are strongly saline or saline-alkali as well, for example the soils of the Mesopotamian plain.

(6) Slightly or moderately calcareous soils with a weakly developed B horizon:

Camberthids (USDA); Xerosols (FAO/Unesco).

These soils occur in semi-arid climate usually on Pleistocene alluvial deposits or loess deposits. They have a fairly good structure and a fair amount of organic matter in the subsoil. They present the least problems amongst the calcareous soils. These soils occur in the semi-arid parts of Jordan, Lebanon, Syria, Iraq, Iran, Pakistan, Yemen and possibly other countries.

(7) Calcareous very clayey soils: Xererts and Usterts (USDA); Chronic and Haplic Vertisols (FAO/Unesco).

These soils have a very high content of expanding type clays (montraorillonite). Their main problems are tillage and lack of internal drainage. Problems connected with lime are minor, although important for some crops. Such soils are extensive in Sudan but occur in small areas in Lebanon, Syria, Iraq and Pakistan.

2.2.2 Calcareous soils of Pakistan

The climate of Pakistan except for the narrow belt in the North is arid to semi-arid. Its aridity is on account of the low rainfall that falls in high intensity rainstorms associated with a high evapotranspiration rate. Varying levels of calcareous soil conditions prevail throughout its terrain excepting the northern narrow belt region. (SF/PAK 6 Report) The general soil descriptions of the prevailing calcareous soils are as follows:

Indus Basin

(1) Calcareous soils with weak structure of semi-arid and arid zones where the CaCO3 content range is 6 to 10 percent in lime nodule form from 90 to 120 cm depth, pH is 8.0 to 8.3. Haplic Vermoeols.

(2) Stratified alluvial soils with moderate calcareous conditions 8 to 10 percent CaCO3, pH ranges from 8,1 to 8.4. Calcaric Fluvisols.

(3) Saline soils of the flood plains with moderate calcareous condition, pH is 8.0 to 8.4. Solonchaks.

(4) Calcareous loess soils, strongly calcareous. Regosols, Cambisols and Yermosols.

(5) Saline stratified soils of the Indus Delta moderately calcareous. Solonchaks.

Mountains and Deserts: The main rocks are limestones and calcareous shales and sand stones of Tertiary age.
(1) Very shallow residual soils of the mountains - very shallow over rock mainly limestone, calcareous shale and sandstones. Calcaric Lithosols.

(2) Strongly calcareous soils of mountain valleys - silt loam and strongly calcareous - the fine soil material and gravel are calcareous. Yermosols, Xerosols, Fluvisols and Regosols.

(3) Very strongly saline soils of playas in western mountain areas - soil material calcareous and stratified. Takyric Solonchaks.

(4) Soils of the sandy desert - the ridges have massive sands that are moderately or strongly calcareous. Regosols.

2.2.3 Calcareous soils of Iran

Seven geologic structural units in sequence characterize the terrains of Iran from the south-west to the north-east. These are: (a) Khuzistan Plain; (b) Antochthonous Folded Zone of the Zagros System; (c) Thrust Folded Zone of the Zagros System; (d) Central Plateau; (e) Elburs range; (f) The Kopet-Dagh or Turkoman Khurasan range; (g) Caspian Littoral. Limestone formations within these geologic structural units are common. Consequently, the soils which are formed contain varying levels of CaCO3 contents. The main soil associations that were mapped by Dewan and Famouri (1964) are: (1) Soils of the plains and valleys; (2) Soils of the plateau; (3) Soils of the Caspian piedmont; (4) Soils of the dissected slopes and mountains. Two thirds of Iran is arid with Calcic Yermosols and strongly calcareous Haplic Yermosols and also Calcic Xerosols.

Calcareous soil conditions characterize the following soil groups within the soils of the plains, soils of the plateau and soils of the dissected slopes and mountains: Alluvial soils and their sub-associations; Grey and Bed Desert soils; Sierozem soils; Brown soils; Chestnut soils; Desert soils and their sub-associations; Calcareous Lithosols and Regosols.

2.2.4 Calcareous soils of Iraq

The chains of mountains Tauros and Zagros that separate Iraq from Turkey and Iran respectively have predominantly calcareous rooks, mainly limestone. The soils of the old fluviatile terraces, floodplains, deltas and marsh estuary, as well as those of the eastern and fan Mesopotamian Plains contain CaCO3 within a range of 20 to 30 %.

(Buringh, 1960). In all these regions, the CaCO3 soil constituent is associated with varying levels of saline and saline-alkali (sodic) soil conditions. According to Al Tai (1968) the crystal fabric is the dominant plasmic fabric in the soils of the Mesopotamian Plain, the main constituents of which are primary calcite and intercalcary crystallites of clay, silt and sand uniformly distributed in the s. matrix. The following soil groups amongst many others, were identified by Al Tai (1966). Under the Entisols: Typic Chromo Xererts, Entric Chromo Xererts; under the Aridisols Typic Calciorthids, Mollic Calciorthids, Lithic Calciorthids and Petrocalcic Paleargids.

In his study on the lime (CaCO3) content of the Lower Mesopotamian Plain Soils in relation to the water analysis of the Euphrates and Tigris rivers, Delver (1960) noted that whereas the range of lime content varied between 20 to 30% in the floodplain zone, the range in north Iraq was from 40 to 70% and that a high fraction of this lime was in the sand fraction. Delver (1960) further noted that the Tigris river sediment contained more lime on an average than the Euphrates river sediment and that the lime was more concentrated in the silt and clay fractions and not in the sand fraction. It is deduced from this finding that the rivers in their transporting action sediment the lime in the form of concretions with the sand in the higher lying areas of the rivers.

2.2.5 Calcareous soils of Jordan

In Jordan, Turonian and Eocene geologic formation series Ajlum and Balqa respectively are mainly composed of limestone, marls and basalt chalk. These geologic rode series prevail in important agricultural areas in east Jordan. The soils that form from the weathering of these rooks are mainly silty clay and clay calcareous soils. Even in the high rainfed areas, CaCO3 content in soils ranges between 20 to 25%. In the dryland areas, lime content exceeds 50%. According to Moorman's Soil Survey Report and Soil Map (scale 1:106, FAO), the prevailing zonal soils in east Jordan are the Grey Desert, Yellow Mediterranean (Brown) and Bed and Yellow Mediterranean (including Terra Rossa). They are predominantly calcareous; CaCO3 content ranges from 30 to 50%. Calcareous soils also prevail in the azonal Grumosols, Rendzinas, Brown, Solonchak, Vertisols, Regosols and Lithosols.

2.2.6 Calcareous soils of Lebanon

The geologic origin of all the sedimentary rocks of Lebanon are calcareous. The parent material of the soils of Lebanon originates directly or indirectly from these sedimentary rooks. These soils vary in the form, content and pattern of distribution of the CaCO3 constituent.

The Jurassic deposits - hard dolomitic rocks form the base of Mount Lebanon and the Anti Lebanon mountain chain. Overlying the Jurassic are the Cretaceous sediments. These sediments cover the west of Mount Lebanon and south-west of the Anti Lebanon mountains. Marl and other limestone deposits overlie the centre west zone. In the south, Eocene hard and soft limestone deposits occur. The coast is formed from Miocene and Pliocene marl and clay sediments. In the Quaternary the water and wind transporting agencies were active thus forming the alluvial and colluvial sediments of the Beqaa plain and the sandy coastal plain.

The following soils have been identified and characterised:

Soils overlying calcareous rocks: Red soils (Terra Rossa) at an altitude of 1 450 to 1850 m highly decalcified (i.e. eluviated) clay 20-40% CaCO3 content 0-6% pH 6.7 to 7.3. Yellow mountain soils less decalcified, CaCO3 content 3-10%, pH 6.4 to 7; Brown soils Clay 30-75%, CaCO3 4-10% pH 7 to 7.6.

Soils overlying marl: Red, yellow, blade and grey, light grey and white Rendzinas, clay 5-25% CaCO3 range of 13 to 80% and pH 7 to 7.6.

Soils overlying sandy and greyish parent material: Sandy coastal soils, CaCO3 6-12% (free of concretions) or 40-60% (concretions present) sand 70-98% and pH 7.4 to 7.8.

Soils overlying basalt : Clay 22-50%, CaCO3 1-5% and pH 6.4 to 7.3 north Akkar and central south Beqaa.

Intergrade soils: Formed from a heterogenic mixture of colluviated material, Band, clay, marl, geologically old CaCO3, and basalt. These soils vary in their stage of pedogenesis and characteristics.

Black or grey soils: The parent material of these soils is the colluviated material from which marl originates. They are hydromorphic -clay 30-35% (Akkar) or 4-10% (Beqaa), CaCO3 varies from 3.5 to 87% and pH 7.2 to 8.

Steppe sub-desertic soils: Light chestnut soils, clay 16-30 % CaCO3, 15-30 % and pH 7.4 to 7.6. CaCO3 may form a hardpan at the surface.

Yellow sub-desertic soils; North Beqaa and Anti Lebanon. Average annual rainfall less than 300 mm. Clay 4-11% fine sand 35-65%, CaCO3 30-45% and pH more than 7.4.

Soils overlying alluvium; No pedogenesis and variable in character according to local conditions.

2.2.7 Calcareous soils of central Sudan

The CaCO3 content is the most significant constituent of the Vertisols of central Sudan where the Gezira and other major agricultural projects are located. (Buursink, 1971) CaCO3 and not MgCO3 predominates in these strongly calcareous central Sudan alluvial soils. Non-calcareous soils, in general, occur in areas where the average annual rainfall is 750 mm and above, i.e. southward. A high degree of positive correlation exists between both the CaO and CaCO3 which may constitute 5 percent of the mineral soil composition supplied by the silt textural fraction.

The phenomenon that the CaCO3 is incorporated with the silt size fraction in the Blue Nile and Nile throughout central Sudan may be attributed to the fact that the salt in the water of these rivers is mainly CaCO3 which, by evaporation, is precipitated in the silt fraction of the sedimented silt.

A wide range of CaCO3 content usually exists in the older alluvial terraces reaching to 51 percent but lower in the recent alluvial terraces. Here, the CaCO3 has been observed in four authigenic forms: (1) few shell fragments in the top 50 cm; (2) few to frequent small to large hard black to grey nodules decreasing to the 1 m depth; (3) few to frequent small to large soft powdery to yellow or brownish irregular concretions to 1 or 2 m depth; (4) few to dominant specks, dondrites, streaks, aggregates masses in soil particles in various horizons.

2.2.8 Calcareous soils of the Arab Republic of Egypt

The main soils of the Nile Valley and the Delta of the Arab Republic of Egypt are Anthropic Glesols and Anthropic Entric Fluvisols (Elgabaly et al. 1969). The range of CaCO3 content in the alluvial soils of the Nile Valley and Delta varies from 1 to 3 percent. The main soils with medium to high CaCO3 content (3 to 30 percent) are those that border the fringe zone of the Nile Valley. Beyond the .fringe zone of the Nile Valley and Delta eastwards and westwards the CaCO3 content in soils increase to a range of 30 to 80 percent and higher. In these eastern and western desert zones, Elgabaly et al. classified these calcareous soils as follows:

Limestone Lithic Ermolithosols - the soil mapping unit for north and central parts of the Western Desert; Limestone Lithic Ermolithosols and Takyric Solonchaks for the Tertiary limestone plateaux near Siwa and Qattara Depression) Limestone Lithic Ermolithosols, Takyric Solonchaks and Lithosols for the geomorphologic transition between the Eastern and Western Deserts; Gravelly Ermolithosols for the Upper Terraces of the Nile and Dry Wadis; Argillic Ermolithosols for the Kharga and Dakhla Oases; Entric Regosols for the Middle Terraces of the Nile Valley and the Sinai terrains; Takyric Solonchaks and Dynamic Ergosols for the Farafra Oases; Marshy Solonchaks and Ochric Solonchaks for North Sinai to Lake Mariut; Marshy Solonchaks, Humic Solonchaks and Solonetz for the partly reclaimed North Delta zone; Salipet Regosols and Ochric Solonohaks for the North Depression of Siwa, Qattara and Wadi el Natrun. Salipetrosols, Ochric Solonchaks and Dynamic Ergosols for the fringe of Siwa and Qattara Depressions; Ermosols for the North West Coastal Region; Dynamic Ergosols for the plateau areas and depressions; Semistatic Calcic Ergosols for the northern sea coast of Abou Kir Bay.

2.3. Investigations on the Reclamation and Land Use of Calcareous Soils in the Arab Republic of Egypt and Lebanon

Relative progress has been realised in the investigations on the reclamation and utilization of calcareous soils in a few countries of the Near East Region and in particular in the Arab Republic of Egypt and Lebanon.

2.3.1 Arab Republic of Egypt

In the Arab Republic of Egypt, the calcareous soil areas that are being reclaimed - a result of the construction of the High Dam are estimated at 300 000 feddans (1 feddan = 1.05 acres) most of which lie west of the Nile Delta where the mean annual rainfall is 110 mm. The CaCO3 content of the soils in this area is 20 to 43 percent, the origin of which is the sedimentary parent material. The CaCO3 distribution in the soil profile is either uniform or localized caliche layers at varying depths from the surface.

The main reclamation and land utilization problems of these areas are:

(1) Crusting of the surface.

(2) Cemented condition of the subsoil layers.

(3) Low availability of phosphorus.

(4) Problems of potassium and magnesium nutrition as a result of the nutritional imbalance between these elements and calcium.

(5) Problem of micronutrient availability.

(6) Problems of water availability.

The main results of field experiments on the problems of highly calcareous soils were the following:
a) Seeding to corn immediately following irrigation and at the lowermost third segment of the furrow.

b) The effects of the levels of apparent density followed by soil moisture level, texture and CaCO3 content were the factors in descending order of their effect upon reducing seedling emergence. Silt was the textural fraction with the highest effect in inducing surface crusting

(2) The Lebaa Agricultural Experiment Station (Litani Project area) is experimenting with vegetable crops grown on highly calcareous soils under rainfed and irrigated agriculture. The highly calcareous Maghdoncke series on the terraced area has a silty clay texture, montmorillonite clay, 53 percent CaCO3 and 22 percent active CaCO3. The Kfar Falouse series on the low-lying area is silty clay loam with less montmorillonite mixed with kaolinite. The total CaCO3 is 84% and the active CaCO3 is 38%. Crust formation is a common feature of this series. The crops that tolerate to varying degrees the calcareous soil conditions are: vegetable crops (some), grapes, stone fruits, lequat (Akkedunya), peaches, plums, almonds, apricot, pomegranate, quince, mulberry, forage crops, legumes and grasses. Deep sub-soiling coupled with legume grass mixtures and organic manure application are considered the soil management improving practices.

(3) The Tyr Agricultural Experiment station's main activities are related to citrus production and crop water requirements.

(4) In Farar Research Station, plant nutrition department, research work in the laboratory is focused on plant nutrition and physiology and chemistry of calcareous soils. The mineralogy of the clay constituent in forty-one soil series, located in the main agricultural zones, has been identified. The fertility status and fertilization requirements could be assessed on the basis of the clay mineralogy identification. The chemical characteristics calcareous soils in relation to lime induced chlorosis are being investigated. The effect of the textural conditions of lime upon soil fertility is also being studied.

(5) The American University of Beirut is conducting research on the fertility of calcareous soils and plant nutrition.

2.4. Achievements

The pressure of increased population combined with the scarcity of the irrigated zone of the Nile river valley and delta prompted the Government of the Arab Republic of Egypt to expand the cultivated terrain to selected areas of the fringe and desert plateau zones adjacent to the Mile river valley and delta zone. This major decision in the history of land and water development of the Arab Republic of Egypt was taken when the High Dam Project was under construction. A total of 770 thousand feddans of calcareous soil areas are in the process of being reclaimed, improved and managed. This area is planned to be expanded to cover a total of 2 million 637 thousand feddans as soon as the 9 milliard cubic meters of more water become available to the ARE from the High Dan Project. The areas that have been reclaimed are estimated at 600 000 feddans.

In Lebanon land and water development activities have been carried out in highly calcareous soil areas. The Northern Region, Akkar Plain mainly, was subject to an SF/FAO Pilot Hydro-Agricultural Development Project. The Green Plan Organization operates in providing services to farmers for establishing terraced cultivated farms afforestation and soil and water conservation practices in the highly calcareous soils of the mountains and plains and coastal plain areas of Lebanon. Since its establishment in the mid 1960's a total of more than 8 000 hectares areas have been developed.

Several similar examples can be cited in the other countries of the Near East Region where calcareous or partially calcareous soil areas have been or are being currently developed. In Iraq a number of land reclamation and improvement irrigation

c) Organic manure application proved useful.

d) An interaction effect between nitrogen and potassium fertilization of wheat and barley was significant.

e) Organic manure application and micronutrient spraying of fruit trees corrected the chlorosis condition due to iron deficiency.

f) 15 to 30 pounds per feddan application of ferrous sulphate, zinc sulphate and manganese sulphate to soils or by spraying at the rate of 3 lb. iron per feddan, resulted in highest yield of corn and barley.

g) Barley tolerates higher levels of boron in calcareous soils than does corn.

h) To induce the water infiltration through calcareous hardpan subsoil layers, heavy irrigation application at short intervals proved successful.

i) Subsoiling at 70 cm relieved the cemented hardpan layer.

j) Prior to the transplanting of grape vines deep holes are made to break the hardpan layer. Areas with hardpans should be avoided to avert secondary salinization effects.

k) Growing of alfalfa on calcareous soils with hardpan proved beneficial in relieving this condition.

1) The cropping pattern suitable for the initial stage of land utilization of highly calcareous soils is the following;

One-third of area

Alfalfa

One-third of area

Berseem (Trifolium alexandrium) clover followed by maize

One-third of area

Small grains followed by cowpeas (lubia) for forage

At the termination of the initial stage of land utilization of highly calcareous soils, the following cropping pattern is recommended:

One-third of area

Grape vines

One-third of area

Alfalfa

One-sixth of area

Small grains followed by maize for surer crop

One-sixth of area

Legumes in winter followed by .summer vegetables


2.3.2 Lebanon

(1) The Tel Amara Agricultural Experiment Station is carrying out soil fertility field work on soils which are calcareous with varying levels of active CaCO3 content. Research has been conducted on wheat nitrogen fertilization and potassium fertilization of sugarbeets. A number of basic investigations are being carried out on water require- and drainage projects with a total of more than 100 000 hectares of partially calcareous soils are being developed. In the Syrian Arab Republic the Euphrates Project area - a basically calcareous soil area - is in the process of being developed for irrigation and drainage. In Jordan the SF/FAO Sandstone Aquifer Project identified rich groundwater resources suitable for irrigated land use of predominantly calcareous soil terrains.

2.5. Conclusions

1. The occurrences of calcareous soils is widespread in all the countries of the Near East Region.

2. Relatively good progress has been made in the reclamation and utilization of calcareous soils carried out in the Arab Republic of Egypt and Lebanon.

3. To realize effective solutions to the field problems of calcareous soils it is necessary that a concerted cooperative approach be taken by the countries of the Near East Region along the following courses of action:

(a) Delineation through soil survey field operations the calcareous soil areas that are acutely afflicted with the problems of lime induced chlorosis. This field study is to be combined with a detailed characterization of the soils of these areas.

(b) Establishment of representative pilot experimental areas for the conduct of laboratory/greenhouse/field experimentation on:

(i) Multivariant single or double factor experiments;
(ii) Multivariant multifactor experiments.
The subject-matter of this programme of applied research and experimentation may be selected from the relevant facets of soil physics, soil chemistry, soil microbiology, soil fertility, clay mineralogy and plant nutrition. As an integral part of the latter approach, field experiments on the following factors are proposed: cultural practices; cropping pattern; irrigation and drainage practices, amendment application and fertilizer use.

(c) Establishment of representative pilot development areas on land and water use of calcareous soils for which a cropping pattern of relevance to the local rural community be implemented. Account has to be taken in this respect to apply the pertinent reclamation, improvement and management practices for calcareous soils. Since these field operations have to be carried out on profitable agricultural production economic grounds, it is imperative to keep the input-output record on the field operations. This information has to be duly analysed and interpreted in terms of the criteria of economic profitability.

(d) Collection, reviewing, analysing, and dissemination of the literature on relevant problems of calcareous soils published in the countries where progress has been achieved in this line of action.

REFERENCES

Al Tai, F.H. 1968, The Soils of Iraq, Ph.D. Dissertation, State University of Ghent, Belgium.

Buringh, P. 1960, Soils and Soil Conditions in Iraq. Directorate General of Soils and Land Reclamation, Abu Ghraib, Iraq.

Buursink, J. 1971, Soils of Central Sudan. University of Utrecht. Utrecht, Netherlands.

Delver, I.P. 1960, Saline Soils in the Lower Mesopotamian Plain. Directorate General of Soils and Land Reclamation, Abu Ghrain, Iraq.

Dewan, M.L. and Famouri, J. 1964, The Soils of Iran. FAO, Rome, Italy.

Elgabaly, M.M. et al. 1969, Soil Map and Land Resources of UAR, Institute of Land Reclamation, Alexandria University, UAR. Res. Bull. No. 22

FAO/UNDP/SF PAK 6 1971, Technical Report: Soil Survey Project, Pakistan - Soil Resources in West Pakistan and their Development Possibilities. FAO, Rome, Italy.

3. Morphology, Mechanical Composition and Formation of Highly Calcareous, Lacustrine Soils in Turkey

by

T. de Meester
Department of Soil Science and Geology
Agricultural University, Wageningen, Netherlands

SUMMARY

The Great Konya Basin is in the South of the Central Anatolian Plateau in Turkey. It is a depression without outlet to the sea. The central part of the basin is the floor of a former Pleistocene lake. This area has highly calcareous clayey sediments and is flat and level. The best drained parts of it were mapped as Steppe Marl Soils (Carbonatic Mallic Calciorthids) and are mainly cultivated with dry-farmed wheat. Small areas are irrigated.

The non-cultivated parts have a degraded steppe vegetation (Virgin Steppe Marls) and their structure is granular in the surface soil due to a high biologic activity. The subsoil of all Steppe Marls is very fine compound prismatic. The cultivated soils show a degradation of soil structure including a clearly compacted plough bottom. This degradation of soil structure is more pronounced if the soil is slightly saline-alkaline.

The profile of irrigated Steppe Marls has a severely degraded surface soil structure due to puddling but it is salt-free and subsoil structure is improved by biologic activity as a result of increased moisture.

The soil texture without removal of carbonates is mostly clay to silty clay and is slightly finer textured after carbonates have been removed. The carbonates (mainly calcium carbonate as calcite) occupy about an equal proportion of the clay, silt and sand fraction (with more than average in the fraction 2-8 cm). Clay minerals of the smectite group are commonest.

The carbonatic clayey parent material of the concerned Marl Soils is a sediment of about 60% mainly chemically precipitated calcite, debris from limestone and shells. The rest is a residue of non-calcareous clay minerals of residual and alluvial origin and sand sized mineral grains of alluvial or aeolian origin. This material is homogenized by organisms.

3.1. Introduction

The concerned soils are situated in the Great Konya Basin in the south of the Central Anatolian Plateau. The central part of this basin is the floor of a former Pleistocene lake. This area, called the Lacustrine Plain, has highly calcareous clayey sediments and is flat and level, except for ancient shorelines which form Randy ridges and beaches. Its soils have been studied in the summers of 1964-68 as part of the Konya Project, a research and training programme of the Department of Tropical Soil Science of the Agricultural University of Wageningen, the Netherlands (de Meester, Ed., 1970, de Meester, 1971).

The soils of the Lacustrine Plain were mostly formed in white, uniform carbonatic clay, but differ markedly in composition and morphology, because of past and present differences in hydrology, topography and vegetation. The climate at present is semi-arid with hot, dry summers and cold, moist winters. The annual precipitation is about 300 mm, mainly falling from November to April. Total evaporation exceeds precipitation by 1000 to 1500 mm. The frost-free season is about 165 days.

The soils of the Lacustrine Plain have been studied and mapped on a regional basis and divided into 3 main types: Steppe Marl Soils, Marsh Soils and. Playa Marl Soils, respectively classified mainly as Calciorthids, Haplaquolls and Haplaquepts. As the two last mentioned types of Marl Soils are strongly salt affected and therefore, amongst other reasons, not so suitable for agriculture, this paper will concentrate on the Steppe Marl Soils. Steppe Marl Soils developed in the best drained parts of the plain. They are not or seldom liable to flooding.

3.2. Steppe Marl Soils

Though the profiles of Steppe Marl Soils have many common features, they differ because of use and degree of salinity. Four examples have been selected to demonstrate those differences: Profile C 3.1 (Fig. 1) of a dry, never cultivated soil, profile C 3.2 (Fig. 2) of a dry, cultivated soil, profile G 1.1 (Fig. 3) of an irrigated soil, and profile D 31 (Fig. 4) of a dry cultivated, slightly saline-alkali soil.

The surface soil is always light-olive-grey to greyish and olive-brown, with an organic carbon content of 0.5-1.7%. The subsoil is invariably pale-olive with clear or faint iron oxide mottles and no organic carbon at all. Very characteristic is the crumb-like structure of the surface soil, resulting from intense biologic activity.

The profiles from the dry cultivated sites (C 3.2 and D 3.1) show a very clear plough bottom (Ap2). The subsoil has a characteristic, fine prismatic structure consisting of very fine angular-blocky elements. As regards D 3.1 the ECe data indicate that the soil is slightly salt-affected between 0-50 cm and according to its Exchangeable Sodium Percentage (ESP>15, pH about 8.3) saline-alkali below 50 cm.

For all soils the calcium carbonate equivalent ranges from 30 to 70%. The surface soil is often less calcareous than the subsoil, presumably because of leaching. In all profiles a calcic horizon occurs at about 50 cm; it represents secondary lime accumulation, as normal in soils of semi-arid regions. The often faint and brownish-yellow (10 YR 6/8) rust mottles cannot be explained as a result of recent oxido-reduction because the substrata of both lacustrine plains are too dry and, permeable, as shown in the moisture studies by Jansen (1970) and by permeability tests. Presumably the widespread yellow mottling has been formed during the last stage when the ancient lake was drying up by fluctuations in watertable near the surface. Thus the mottles are fossil.

The saline-alkali profile D 3.1 has clear coatings (cutans) in the subsurface horizon, resulting from migration of clay-humus compounds mobilized under the slightly alkali conditions presumably existing at the end of the dry season (Driessen, 1970). The first heavy rainshowers wash down some of the surface material, which settles on the peds in the subsurface layer.

The Steppe Marl Soils are irrigated here and there. G 1.1 is a profile from a field that was irrigated for some eight years. The data show that salts have been entirely removed to give a less prismatic subsoil. Due to puddling, however, the structure of the surface soil became subangular-blocky, thus deteriorating as compared with the original crumb-like structures of the nearby dry Steppe Marls, but the subsoil shows biological activity to a greater depth.

3.3. Mechanical Composition of Marl Soil

3.3.1. The analysis

The textural composition was studied, mainly to detect the origin of the carbonate fraction. The plasmic structure of the Marl Soils is mainly porphyroskelic with a fine or very fine crystic plasmic fabric (Fig. 5, terminology according to Brewer, 1964). Hard calcareous nodules and many shell fragments of all sizes are also present. The calcium carbonate equivalent ranges between 30 and 70%. A mechanical analysis of such soil material can be made of the Whole soil or of the non-calcareous part only, but both present some difficulties mainly because dispersion may be hindered by organic matter and lay calcareous cementation. If carbonates are not to be removed, mostly sodium pyro-phosphate is used with good results. For Marl Soils I have found that simple stirring is as effective as 30 minutes in a 500 Watt ultrasonic generator, provided that sodium phosphate (Na2P2O3) is added before or afterwards to keep the particles dispersed.

Gypsiferous samples have first to be washed with water of about 40°C to remove all calcium sulphate. The separation of the fractions by sieving or settling introduces a serious error, because carbonate grains and non-carbonate grains differ widely in shape and density: the sand fraction contains elongated shell fragments and rounded material, the .clay and silt fractions contain carbonate crystals and clay micelles.

For mechanical analysis of the non-calcareous part of a soil, the carbonates are usually removed with cold diluted hydrochloric acid (Diagnosis, 1954). This treatment is insufficient to get rid of hard calcareous nodules, especially those of dolomite, but heating causes serious damage to the minerals (Ruellan, 1970).

All this leads inevitably to errors, so that a grain-size analysis of Marl Soils as such is difficult to interpret.

3.3.2. The grain-size distributions

The grain-size distribution in surface soil and subsoil was determined in some 50 Steppe Marl samples. Fig. 6 shows that the texture without removal of carbonate is mainly silty clay, which confirms the field assessment. The results also show that the texture in the surface of Steppe Marl Soils is slightly coarser than in the subsoil, which is explained by removal of the clay and silt fractions by wind.

The difference in texture of Marl Soils before and after removal of carbonates is given in Fig. 7. There was an average increase of about 25 percentage units in clay and a decrease of about 20 percentage units in silt and a decrease of 5 percentage units in the sand fraction.

The distribution of the carbonates over various grain-size fractions as determined by Atterberg's method is shown in more detail in Fig. 8: a rectangle represents a full sample. The percentages are expressed in calcium carbonate equivalent. The CaO/MgO relation has been added for each fraction for further information on the composition of the carbonates. The data show that the carbonate content in the clay fraction ranges from 12 to 43%, in the silt fraction from 26 to 70% (with more than average in the fraction 2-8 µm) and in the sand fraction from 24 to 70%. The calcium carbonate equivalent of the soil is not the calculated average of all fractions, but has been determined on the full sample. Differences are within the experimental error.

The carbonate parts of the fractions may contain grains with smaller non-calcareous particles which should be added to the non-carbonate fractions. Table 1 shows, however, that the amounts vary considerably. Because the samples have been too small to obtain very accurate data, no corrections have been made in the totals per fraction.

Table 1. Non-carbonate components in Marl Soil fractions (profile E 3.1)

Particle size in Marl Soil fraction

Depth

Particle size in Marl Soil fraction

Percentage particle-size distribution in non-carbonate fraction

(cm)

µm

8-50 µm

2-8 µm

<2 µm

0-5

2-8

-

58.5

41.5

105-170

2-8

-

86.1

13.9

0-5

16-50

100.0

0.0

0.0

105-170

16-50

84.0

2.7

13.3


3.3.3. Carbonate minerals

So far, the carbonate part of the Marl Soils, consisting of calcium and magnesium carbonates, has been expressed in calcium carbonate equivalent. The CaO/MgO relation in Fig. 8 shows that calcium carbonate predominates.

In addition, X-ray diffractograms have been made of 18 samples from six representative Marl Soils to obtain some semi-quantitative information on calcite, dolomite and aragonite in the carbonate minerals. Table 2 shows that almost all samples contain at least 85% calcite; the rest is dolomite. A few samples have less calcite and some aragonite, apparently from aragonite-bearing shells of Dreissena.

In the clay, silt and sand fractions separately, no carbonate minerals have been estimated. But differences may be expected, as morphological studies have revealed that the silt and sand fractions contain more shell fragments than the clay, whilst the clay and fine silt fractions consist of chemically precipitated carbonate crystals (see next paragraph).

3.3.3. Formation of Marl Soils

Several of the Guinier de Wolff X-ray diffractograms of Marl Soil samples show sharp lines for calcite and for dolomite, which indicate that these minerals occur in a well crystallized form. Together with observations on thin sections (Fig. 5) and with the electron scanning microscope, this strongly suggests that the carbonate clay fraction of Marl Soils is mainly formed by chemical precipitation, presumably in the shallow parts of the Ancient Konya Lake. A high pH, saline-alkali condition and water rich in bicarbonates of Ca2+ and Mg2+ may promote this. Withdrawal of CO2, partly during photosynthesis, eventually in combination with diurnal changes in water temperature, easily result in precipitation of calcium carbonates, and of dolomite which is less soluble (Skinner, 1963).

Table 2. Carbonate minerals in the carbonate part of Marl Soils derived from Guinier de Wolff diffractograms. The relation CaO/MgO is added for comparison.

Sample No

Profile

Depth (cm)

Calcite
%

Dolomite %

Aragonite %

CaO/MgO

CaCO3 equiv.(%)

1

A 11



20- 32

about 90

about 10


6.5

67.5

2

40- 58

about 90

about 10


6.2

74.7

3

102-148

80-90

10-20



59.4

4

E 31



0- 5

>95

<5


10.8

45.9

5

30- 52

>95

<5


11.3

59.0

6

105-170

>95

<5


12.4

44.6

7

D 31



0- 17

>95

<5


13.8

38.2

8

21-45

>95

<5


10.0

48.5

9

90-140

>95

<5


11.0

42.3

10

G 1.3



0- 25

>95

<5


12.9

59.0

11

35- 80

>95

<5


12.1

50.0

12

80-120

>95

<5


10.5

75.8

13

G 2.3



0- 10

>95

<5


6.2

41.2

14

55- 80

>95

<5


10.0

37.8

15

80-120

about 95

about 5


20.0

54.3

16

E 1.3



0- 5

about 85

about 10

<5

7.8

61.8

17

15- 30

about 75

10-20

<5

4.6

59.6

18

30-100

about 75

10-20

<5

4.2

57.7


Carbonates are still precipated on a small scale in the Lacustrine Plain, as observed in July 1967 in a shallow saline temporary lake where ooze of almost pure crystalline calcite formed almost 3 cm thick. The area soon dried up. In day-time the pH of the ooze was 8.8 .

Thick crusts of precipitated carbonates on waterplants were observed also in July 1967 in another small shallow saline pool. At 10.00 h the pH was about 10 in the middle and 7.5 near the shore; concentration of and HCO3, were 2.75 and 6.38 meq/l, respectively. There was little change in pi at night, so that vegetation did not seem the direct cause. The extreme pH in both sites suggests the presence of sodium carbonate, which could certainly cause precipitation of calcium carbonate. X-ray diffractograms of these precipitates show mainly calcite, with less than 5% dolomite. The electron scanning micrograph shows typical carbonate crystals in ooze and crusts.

After drying up, the precipitated carbonate sediment was on both sites about 0.4 cm thick. Already in the muddy stage, numerous organisms had started working the material. A few weeks later, the precipitated crust had completely disappeared from the surface by the activity of organisms and by cracking after drying. The material was mixed with parts of the surface soil.

Presumably Marl Soils in the Lacustrine Plain initially formed in this my,

In summary, it seems that the carbonate clay and fine silt fractions in the Marl Soils mainly originate from precipitation and that the non-carbonate clay component has been blown and washed in or has been formed in situ. The coarser carbonate fractions are crushed shell fragments, limestone debris from coastal erosion, and secondary aggregates. The coarser, non-calcareous components are carried in by rivers and wind. Finally the resulting calcareous soil material is homogenized by organisms.

Fig. 1. Field description and analytical data of Profile C 3.1

diagnostic horizons:

Ochric epipedon


Cambic horizon


Calcic horizon

classification (19.67):

Fine carbonatic Mollic Calciorthid.


Fig. 2. Field description and analytical data of Profile C 3.2

diagnostic horizons:

Ochric epipedon


Cambic horizon


Calcic horizon

classification (1967):

Fine carbonatic Mollic Calciorthid.


Fig. 3. Field description and analytical data of Profile G 1.1

diagnostic horizons:

Ochric epipedon


Cambic horizon


Calcic horizon

classification (1967):

Fine carbonatic Mollic Calciorthid.


Fig. 4 Field description and analytical data of Profile D 3.1

diagnostic horizons:

Ochric epipedon


Cambic horizon

classification (1967):

Fine cartonatic Mollic Canborthid.


Fig. 5. Photomicrograph of a thin section from Profile C 3.1 (depth 20 cm), (1) vughs, (2) mixed loose cystic fabric, (3) shell fragment, (4) skeleton grains. Photographed with polarized light.

Fig. 6. Texture of surface soil (I) anil subsoil (II) of Steppe Marl Soils (50 samples from 12 profiles).

Fig. 7. Texture of Marl Soils before (I) and after (II) removal of carbonates (30 samples).

Fig. 8. Percentage of calcium carbonate equivalent per size fraction in 5 samples from a Steppe Marl Soil. Dotted line (a) is percentage calcium carbonate equivalent in whole sample.

REFERENCES

Diagnosis and Improvement of Saline and Alkali Soils. Agricultural Handbook 60, US Dept. of Agr. Washington D.C.

Driessen, P.M. 1970, Salinity and Alkalinity in the Great Konya Basin. Agr. Res. Rep. 743, (Pudoc Wageningen).

Janssen, B.H. 1970, Soil Fertility of the Great Konya Basin, Turkey. Agr. Res. Rep. 750, (Pudoc Wageningen).

Meester, T. de. 1970, The reconnaissance survey. In: T. de Meester (Ed.), Soils of the Great Konya Basin, Turkey, part A 1-146. Agr. Res. Rep. 740, (Pudoc Wageningen).

Meester, T. de. 1971, Highly calcareous lacustrine soils in the Great Konya Basin, Turkey. Agr. Res. Rep. 752, (Pudoc Wageningen).

Ruellan, A. 1970, Contribution á la connaissance des sols des régions méditerranéennes les sols a profil calcaire différencié des plaines de la Basse Moulouya (Maroc oriental). Thèse Fac. Sci. Strasbourg.

Skinner, H. Catherine. 1963, Precipitation of calcian dolomites and magnesian calcites in south-east of South Australia. Am. J. Sci. 261: 449-472.

DISCUSSION

The discussion concerned terminology; "calcareous" is a general term for soil containing CaCO3, "carbonatic" is well defined and "Marl" is used in geology, soil science and the cement industry for soft lime; and about the pH in relation to the presence of sodium carbonate. It was accepted that small amounts of magnesium carbonate can raise the pH considerably, but presence of sodium carbonate will give the highest pH.

4. Nutrient Supply and Availability in Calcareous Soils1/

by

S. R. Olsen
Soil Scientist
USDA, Port Collins, Colorado, U.S.A.

1/ Contribution from Agricultural Research Service, USDA, in cooperation with Colorado State University Experiment Station.
SUMMARY

1. An evaluation of the P status of calcareous soils will probably lead to methods for making more quantitative fertilizer recommendations. Such methods will a) help correct P deficiencies where they exist, b) help recognize when a soil has an adequate supply of P, and c) help detect soils abundantly or amply supplied with P where continued fertilizer application may be wasteful economically. The excess supply of P in such soils may cause micronutrient deficiencies with Fe, Mn and Zn. If runoff or erosion occur from such soils into streams and lakes or reservoirs, pollution problems may arise from excessive algal growth.

2. The rate of P uptake by roots in a given soil was a linear function of the P concentration in the soil solution, or approximately linear in the range of concentrations from deficient to an adequate supply. However, when soils of various textures are compared at the same moisture suction (0.33 bar) the rate of P uptake was the same when the P concentration varied eightfold. The P supplying power of the various soils is explained by taking into consideration the differences between the soils in their diffusion coefficient of P and their capacity factors (the amount of P from the solid phase that will come into the soil solution for a unit change in concentration of P). An equation based on diffusion of P to roots takes into account these differences.

3. The equation may be used to calculate the concentration of P needed in soils varying in texture in order to obtain equal rates of P uptake by roots. Assumptions must be made for the concentration of P at the root surface, the root radius, and a rate of uptake that will assure an adequate supply of P for the crop. Applications of these methods have not been tested under field conditions.

4. Curves may be constructed to represent the reaction of fertilizer P with the soil after several wetting and drying cycles. These curves could be made for soils representing ranges in texture, CaCO3 content, or other soil properties known to affect the reaction of fertilizer P with the soil. From the equation the concentration of P in the soil solution [or potential expressed as p(H2PO4 + HPO4)] required for equal rates of P uptake may be calculated. From the reaction curves the amount of fertilizer P corresponding to the needed P concentration may be determined. The curve could also be constructed by using extractable P by the NaHCO3 method (or other suitable methods). As a practical guide the level of NaHCO3 extractable P for an adequate P supplying power to the roots will range from 15 ppm P on sandy soils to 20 ppm P on clay soils.

5. The soils which had an equal power to supply P to the roots contained approximately equal amounts of extractable P by the NaHCO3 method. If the extractable P is expressed on a volume weight basis, the value for soils varying in texture tend to be more nearly the same when the soils have equal supplying power for P to plant roots.

4.1 Introduction

The phosphorus status of calcareous soils must be evaluated before quantitative fertilizer recommendations can be made. Usually, we rely upon soil tests, field trials including rates of P, previous history of cropping and fertilization, the crop to be grown, and the expected yield. These empirical approaches can be improved as we gain further knowledge and understanding of fundamental processes in soil-plant relationships. We must acquire more information about the nutrient supply characteristic of the soil and the environment and connect this knowledge to the nutrient supply required by the plant for optimum growth rates.

The process of nutrient supply can be divided into various steps as indicated in equation (1) (Fried and Broeshart, 1967):

M (solid) M (solution) M (plant root) M (plant top)

(1)


where M is nutrient ion. Nutrient supply involves all these steps which occur simultaneously, but a steady-state approximation may be assumed. This assumption leads to the concept of a rate-limiting step; i.e., in equation (1) the slowest step determines the rate of the over-all process. The rate of reaction depends on the concentration of the reactants and the rate constant. A complete description of this process opens the way to possible regulation and control through management practices. The concepts illustrated by equation (1) will form a basis to examine the existing knowledge about ion uptake processes from calcareous soils, especially in relation to more efficient use of P fertilizer, and to indicate where new information is most needed.

The transfer of nutrients from soil to crop depicted by equation (1) emphasizes the interdependence of these processes. The soil may possess a certain potential to supply P to plant roots, but the actual amount supplied depends also on the properties of the root such as its length, radius, and its ability to lower the concentration of P at the root surface. This ability is not solely a function of the root but depends in part on the demands for P by the tops. As this concept applies to field conditions, the root density of a given plant becomes an important factor affecting nutrient uptake (Barley, 1970).

These relationships between root and soil are complex and the variables cannot be assigned numbers as yet for the entire growth period of a crop. A more practical approach is to use shorter periods of time for which numbers can be assigned in order to predict and measure the P supply to roots. The supply of P must be sufficient to maintain a given rate of growth and a given P content of the new growth. This rate of growth and P content can be set at different levels which depend on the crop, conditions of growth and the expected yield. Some trials with these objectives in mind have been reported on calcareous soils by applying diffusion theory to the relationships indicated in equation (1) (Olsen and Watanabe, 1970). These concepts will be examined further in this paper with special reference to calcareous soils.

4.2. Equation for Uptake of P

Some of the variables that control P uptake by plant roots can be combined in equations which describe the conditions existing when a nutrient diffuses to a root surface. A simplified initial and boundary condition will be assumed, i.e. a) initially the root surface has the concentration, C = Co when t = 0, and b) C = Cr when t > 0, where C = concentration of P in the soil solution and t = time in seconds. Flux of P to a root was described by an equation under this boundary condition (Olsen, Kemper, and Jackson, 1962).

The integrated form with respect to time of the flux equation appears as equation (2).


(2)


where,

Q = amount of P absorbed in time, t, as g/cm2 of root surface

a = root radius, cm

B = slope of line (b + q) relating labile P in g/cm3 of soil to concentration, C, of P in the soil solution, g/cm3, and q is the volumetric moisture content. B is a capacity factor.

Co = initial concentration, g/cm3

Cr = concentration at the root surface, g/cm3

T = Dpt/Ba2

Dp = diffusion coefficient of P, cm2/sec as defined previously (Olsen, Kemper, and Jackson, 1962)

Numerical values for the graphical solution of equation (2) have been given (Olsen and Watanabe, 1970, see Fig. 1). Numerical values for the graphical solution of the flux equation have been presented (Olsen and Kemper, 1968, see Fig. 2). Other boundary conditions may be assumed (Bouldin, 1961; Nye, 1968; Olsen and Kemper, 1968) but the relationships among the variables in equation (2) will suffice to illustrate the kinds of measurements needed. Practical applications of information gained from equation (2) will be illustrated in the discussion that follows. For example, data from equation (2) explain how roots absorb P at the same rate from soils of various textures which exhibit a 15-fold variation in the P concentration of the soil solution.

4.3. Capacity factor

This capacity factor, B, is an estimate of the amount of P from the solid phase that will enter the soil solution (thus becoming diffusible or available for uptake) for a unit change in P concentration of the soil solution. The capacity factor is important because the P concentration determined at the beginning of the growth period does not give sufficient information on the P supply to plants throughout the growth period. A method of measuring B that was applicable to all soils would be very difficult to find. Mainly, three methods have been tried: a) labile P measured by 32P exchange, b) resin-extractable P, and c) the Q/I relationship (DQ/DI)Io of Beckett and White (1964) or the differential phosphate potential buffering capacity (DPBC) of Jensen (1970, 1971). Jensen defined DPBC as the amount of P to be added or removed per gram of soil in order to obtain a certain alteration of the phosphate potential (0.5 pCa2+ pH4PO). Thus, the differential capacity is used to indicate that the buffering capacity depends on the phosphate potential.

The possibility exists that 32P does not necessarily distinguish between available and non-available forms of P (Aslyng, 1964). Some fertilizer P changes into forms of such low solubility that these forms do not contribute to the available supply of P but such forms still undergo isotopic exchange with 32P. When such reactions occur the 32P method would overestimate labile P and predictions of Q in equation (2) would be too high. However, the use of equation (2) does not offer an accurate way to test the validity of a method to measure a capacity factor because of assumptions made in estimating a value of Cr. Therefore, other approaches should be taken to get an independent way of testing the validity of a given method to measure the capacity factor.

One approach has been to measure the diffusion coefficient (Dp) of P in a soil by two methods, a) one method requires an estimate of the capacity factor to Dp get (transient-state case) and b) the other method provides a measure of Dp that does not require an estimate of the capacity factor (steady-state case). Such comparisons have been made on two calcareous soils and the measurement of labile P by 32P exchange (24 hours) appeared to give a valid estimate of the capacity factor because Dp was essentially the same by either method (Olsen, Kemper and van Schaik, 1965).

A comparison was made of the capacity factor measured by 32P exchange and by anion resin-extractable P (Olsen and Watanabe, 1970). The values agreed closely on three calcareous soils. Studies of the Q/I relationships (Beckett and White, 1964) on these soils is underway.

The capacity factor increases as the clay content of soils rises as shown by data from each method. Labile P represents a surface-active fraction of a number of forms of solid phase P in soil including crystalline, colloidal, or adsorbed phases. The clay appears to promote a larger surface area of the reaction products between soil and fertilizer P (Beckett and White, 1964; Muljadi, Posner and Quirk, 1966; Jensen, 1970; Olsen and Flowerday, 1971).

The capacity factor was approximately constant in soils containing varying amounts of CaCO3 derived from the same geologic origin, but it differed among soils with CaCO3 from various origins. For example, a soil with CaCO3 from Cretaceous Chalk had a capacity factor 2.7 times greater than another soil containing magnesian limestone (Talibudeen and Arambarri, 1964).

4.4. Intensity factor

The intensity factor, usually expressed as the concentration of P in the soil solution, is very important in the relationships shown in equation (2) because the difference (Co - Cr) between the initial concentration and the concentration, Cr, at the root surface mainly controls the rate of P uptake by roots. The concentration, Co, can be measured readily in water extracts or in 0.01 M CaCl2 solution; however, the manner of expressing this concentration in a way which is most significant to plant roots is still not clear, especially for calcareous soils. In acid soils pH below 6 the concentration consists mainly of ions and the intensity factor may be expressed in terns of activity, aH2PO4, pH2PO4, or 0.5 pCa + pH2PO4. In soils having a pH above 6 the presence of ions and a soluble calcium phosphate complex, CaHPO4, must be considered in expressing concentration activity of P.

The relative importance of in P uptake by plants has not been fully clarified, The plant response in soils above pH 6 appears to be correlated better with total P concentration (Aslyng, 1964; Wild, 1964).

Jensen (1970, 1971) presented data showing that a correction for the complex, CaHPO4, was necessary in measuring the DPBC of calcareous soils. He made this correction using an equation derived by Larsen (1965). With this correction the DPBC for three calcareous soils was the same in 0.01 M or 0.001 M CaCl2 solutions whereas the DPBC differed for the uncorrected data.

Although this discussion points out problems and unanswered questions about how to measure and express Co, there is much less information on bow to measure or estimate Cr, the concentration at the root surface. These problems apply to acid and calcareous soils. Hopefully, these problems will be solved because such knowledge is necessary to define the boundary conditions for using diffusion models to predict P supply to roots such as equation (2). Nye (1968) and Barley (1970) have indicated the nature of some of these problems and what experimental approaches may prove fruitful.

4.5. Diffusion coefficient

A third important factor in Dp equation (2) influencing the amount of P uptake by roots is the diffusion coefficient of P, Dp. This value varies with volumetric moisture content, Q, and factors for tortuosity of path length and negative adsorption (Olsen. Kemper and van Schaik, 1965). In several calcareous soils Dp ranged from 5.40 × 10-7 to 1.12 × 10-7 cm2/sec. Values were highest for clay soils and lowest for sandy loams (Olsen and Watanabe, 1970).

4.6. Nutrient supply

The nutrient supply of P in three calcareous soils was evaluated by using equation (2). Textural variations were highly correlated with the ability of these soils to supply P to plant roots. In these soils the roots absorbed P at the same rate when the P concentration, Co, varied fivefold (Olsen and Watanabe, 1970). Equation (2) based on diffusion of P adequately explained the differences in the P-supplying power of these soils varying in texture. Predicted values for uptake of P from equation (2) agreed closely with observed values. An average value for Cr was estimated from two boundary conditions, a) dq/dt is constant and b) Cr is constant when t>0.

The P status of these soils is shown in Table 1. The initial level of Co was lowest for the clay soil but a significant increase in yield of barley in the greenhouse was observed with each soil. Addition of P as concentrated superphosphate (CSP) caused a larger increase in Co in the fine sandy loam than in the clay. This difference reflects the adsorptive capacities of the three soils. Relevant physical and chemical properties of these soils is shown in Table 2.

The diffusion coefficients and values of the capacity factor, B, by two methods are shown in Table 3. Values of Dp and B varied five-fold and ninefold, respectively, as texture differed.

The rate of P uptake by corn roots (24-hour absorption period) was linearly related to P concentration, Co, in each soil. From these the value of Co was estimated when the uptake was constant at 2 × 10-12 g/cm2/sec. These values of Co appear in column 2 of Table 4. A value of Cr for each soil was estimated using two boundary conditions as previously indicated. These values are shown in Table 4.

An average value of Cr from Table 4 was used in equation (2) to calculate Q and the comparison between predicted and observed values appear in Table 5. The observed value was 12 percent lower than the predicted value from equation (2). Better estimates of Cr will likely be possible as we learn more about the soil-root system,

Some practical applications can be made from using equation (2) and data required to solve a value of Q. If a value for Q can be estimated that will allow a plant to attain a high or adequate growth rate, then equation (2) may be used to determine the value of Co required to supply the estimated value of Q. Such calculations also require an estimate of Cr. A relationship between Co and fertilizer P added is also needed. By knowing the required Co from equation (2), the amount of fertilizer P can be determined which will give the necessary value of Co. Such data for three calcareous soils is shown in Table 6. The value of Co needed to give an equal rate of P uptake on these soils varied eightfold. The fertilizer P (CSP) required to raise the P status to the needed level of Co varied twofold. Essentially the sane estimate of fertilizer P needed was obtained by using the corresponding values of Co found in 0.01 M CaCl2 extracts of these soils.

Table 1. Phosphorus status indicated by various measurements as related to level of fertilizer P (CSP).

Soil


P Added

P Concentration

Labile P** (ppm)


Resin-P (ppm)


(ppm)

Water extract* (ppm)

.01 M CaCl2 (ppm)

Pierre



0

.031

.017

17.8

11.0

17.5

.058

.031

24.3

18.0

35

.094

.053

34.4

27.3

Apishapa



0

.104

.034

20.9

15.2

17.5

.209

.092

29.8

24.3

35

.350

.161

42.8

36.4

Tripp



0

.220

.045

10.3

6.3

10

.410

.137

16.6

12.7

20

.800

.305

22.9

18.1

* 40 g soil/50 ml water.
** 31P that undergoes isotopic dilution with 32P in 24 hours.
Table 2. Physical and chemical properties of soils

Soil


pH*


Clay

CaCO3

Bulk Density

H2O at .33 bar

%

%

(g/cm3)

(g/cm3)

Pierre

7.53

51.0

2.9

1.00

.392

Apishapa

7.53

36.6

6.2

1.00

.315

Tripp

7.20

15.0

0.2

1.32

.177

* In .01 M CaCl2.
Table 3. Diffusion coefficients and values of B in three soils.

Soil


Dp

B (Capacity Factor)

cm2/sec

From 32P

From resin-P

Pierre

5.40 × 10-7

267

255

Apishapa

3.23 × 10-7

87.5

86.2

Tripp

1.12 × 10-7

28.7

27.3


Table 4. Concentration of P (Cr) estimated at the root surface.


Soil



Co *

Cr

Cr/Co

Constant Cr condition

Constant dq/dt

Constant Cr condition

Constant dq/dt

g/ml soIn.

g/ml soln.

g/ml soln.



Pierre

0.96 × 10-7

0.57 × 10-7

0.47 × 10-7

.59

.49

Apishapa

1.96 × 10-7

1.08 × 10-7

0.88 × 10-7

.55

.45

Tripp

4.80 × 10-7

2.20 × 10-7

1.59 × 10-7

.46

.33

* Values from curves when uptake equals 2 × 10-12 g/cm2/sec.
Table 5. Comparison of observed and calculated rates of P uptake by corn roots in three soils

Soil


Cr (Ave.)

Q (Calculated) *

Q (Observed)

g/ml soln.

g/cm2/day

g/cm2/day

Pierre

0.52 × 10-7

1.94 × 10 -7

1.73 × 10-7

Apishapa

0.98 × 10-7

1.93 × 10-7

1.73 × 10-7

Tripp

1.90 × 10-7

1.94 × 10-7

1.73 × 10-7

* Calculated from equation (2) and values of Co shown in Table 4.
Table 6. Fertilizer P (as CSP) needed to supply 1 µM P per g of roots per day.*

Soil


Co initial

Co Needed

P (H2PO4 + HPO4)

Fert. P

NaHCO3-P at Co needed

ppm

ppm


ppm

ppm

Pierre clay

.031

.109

5.92

40.5

22.0

Apishapa silty






clay loam

.090

.286

5.60

29.0

21.8

Tripp fine






sandy loam

.220

.845

5.17

20.6

19.6


* Assumptions:

1. Corn roots: a = .035 cm, area - 57 cm2, 1 cm3 roots = 1 g fresh weight.
2. Cr/Co = 0.1.
The phosphate potential, p(H2PO4 + HPO4), is shown in Table 6 for the values of Co in column 3. The potentials were calculated from the pH and P concentrations in 0.01 M CaCl2. A linear relation was observed between the P potentials and the clay content of these soils.

The validity of the assumptions indicated in Table 6 were tested by measuring the yield response of barley to CSP in the greenhouse for each soil. The rates of fertiliser P in table 6 ware calculated based on a concept that these rates would raise the P status so that each soil had the same -P-supplying power. If the estimated value of Q is correct, then the percentage of the highest yield on each soil should fall near 100 far these calculated rates of CSP. At the rate of P as CSP shown in table 6, the percent of the maximum yield on each soil was 93.0, 97.4 and 96.5, and the P concentration in the plants was 0.213, 0.238, and 0.221 percent for the Pierre, Apishapa, and Tripp soils, respectively.

Aslyng (1964) suggested addition of fertilizer P to achieve a constant potential of P to maintain an adequate supply of P on various soils. He recommended a phosphate potential, p(H2PO4 + HPO4), of 5. The data in table 6 indicate that the potential of P varies in different soils When they have an equal supplying power of P to roots, i.e., from 5.17 to 5.92.

With reference to the potentials of known compounds, the solubility of P was calculated for the soils that received the amounts of P shown in table 6. On a solubility diagram these points plotted between the lines for hydroxyapatite (HA) and octocalcium phosphate (OCP), but they were nearer to the line of OCP. The phosphate potential of 5 recommended by Aslyng (1964) has a solubility point that lies very near to the OCP line.

If the solid phase P in a soil has a solubility corresponding to OCP, then the P-supplying power of such soil is likely to be unrelated to soil properties. This reasoning is based on the likely assumption that OCP dissolves rapidly enough to control the P concentration in solution (Lindsay and Moreno, 1960; Webber and Mattingly, 1970a). The data in table 6 indicate that sandy soils fertilized to an adequate level of P may reach a P potential near or equal to OCP. Clay and loam soils showed potentials less than OCP, although they supplied adequate amounts of P to plants. A Barnfield soil, with 31 % clay, studied by Webber and Mattingly 1970b) had a very high P status (NaHCO3 - soluble P was 67 ppm), but this soil in equilibrium with CaCO3 was undersaturated with respect to OCP.

4.7. Research needs

Some areas of research that need attention are indicated below:

(1) The role of P concentration in the soil solution, Co, and at the root surface, Cr, needs evaluating in relation to the rate of P uptake by intact roots growing in soil. This means that information is needed on the proportionality coefficient relating rate of uptake to the P concentration. Such data are needed for different crops during critical growth periods, for various conditions of root growth, age, size, and density of roots. This information will lead to better measurements of the ability of soil to supply P to plants and improve the application of realistic boundary conditions to equations based on the diffusive supply of P to roots.

(2) The uptake of P depends directly on the concentration of P in the soil solution but also on the quantity of P that will be released as the roots lower the concentration over a given range and on the diffusion coefficient of P. The nature and properties of the solid phase P contributing P to the soil solution needs further evaluation and definition. Under some conditions the P concentration may be controlled at a constant level at a given pH by compounds such as OCP or dicalcium phosphate, and the quantity that will be released equals the amount of the compound present. Under other conditions, the P concentration may be controlled by the labile P and its properties. In these oases, the P concentration usually varies linearly with the amount of labile P and the slope of the line is an important factor related to P uptake. Very little is known about the chemical nature and properties of labile P, although its measurement serves a useful purpose.

REFERENCES

Aslyng, H.C. 1964, Phosphate potential and phosphate status of soils. Acta Agric. Scand. 14:261-285.

Barley, K.P. 1970, The configuration of the root system in relation to nutrient uptake. Adv. in Agron. 22:159-201. Academic Press, Inc., N.Y.

Beckett, P.H.T. and White, R.E. 1964, Studies on the phosphate potentials of soils: 3. The pool of labile inorganic phosphate. Plant and Soil 21:253-282.

Bouldin, D. 1961, Mathematical description of diffusion processes in the soil-plant system. Soil Sci. Soc. Amer. Proc. 25:476-479.

Pried, M. and Broeshart, H. 1967, The soil plant system in relation to inorganic nutrition. Academic Press, Inc., N.Y. 358 p.

Jensen, H.E. 1970, Phosphate potential and phosphate capacity of soils. Plant and Soil 33:17-29.

Jensen, H.E. 1971, Phosphate solubility in Danish soils equilibrated with solutions of differing phosphate concentrations. J. Soil Sc. 22:261-266.

Larsen, S. 1965, The influence of calcium chloride concentration on the determination of lime and phosphate potentials of soil. J. Soil Sci. 16:275-278.

Lindsay, W.L, and Moreno, E.G. 1960, Phosphate equilibria in soils. Soil Sci. Soc. Amer. Proc. 24:177-182.

Muljadi, D, Posner, A.M. and Quirk, J.P. 1966, The mechanism of phosphate adsorption by kaolinite, gibbsite, and pseudo-boehmite. J. Soil Sci. 17:212-237.

Nye, P.H. 1968, Processes in the root environment. J. Soil Sci. 19:205-215.

Olsen, S.R., Kemper, W.D. and Jackson, R.D. 1962, Phosphate diffusion to plant roots. Soil Sci. Soc. Amer. Proc. 26:222-227.

Olsen, S.R., Kemper, W.D. and van Schaik, J.C. 1965, Self-diffusion coefficients of phosphorus in soil measured by transient and steady-state methods. Soil Sci. Soc. Amer. Proc. 29:154-158.

Olsen, S.R. and Kemper, W.D. 1968, Movement of nutrients to plant roots. Adv. in Agron. 20:91-151. Academic Press, Ind., N.Y.

Olsen, S.R. and Watanabe, F.S. 1970, Diffusive supply of phosphorus in relation to soil textural variations. Soil Sci. 110:318-327.

Olsen, S.R. and Flowerday, A.D. 1971, Fertilizer phosphorus interactions in alkaline soils. Fertilizer Technology and Use, 2nd Ed., p. 153-185. Soil Sci. Soc. Amer., Madison, Wis.

Talibudeen, O. and Arambarri, P. 1964, The influence of the amount and the origin of calcium carbonates on the isotopically exchangeable phosphate in calcareous soils. J. Agric. Sci. Camb. 62:93-97.

Webber, M.D. and Mattingly, G.E.G. 1970a, Inorganic soil phosphorus. I. Changes in the mono-calcium phosphate potentials on cropping. J. Soil Sci. 21:111-120

Webber, M.D. and Mattingly, G.E.G. 1970b, Inorganic soil phosphorus. II. Changes in the mono-calcium phosphate potentials on mixing and liming soils. J. Soil Sci. 21:121-126.

Wild, A. 1964, Soluble phosphate in soil and uptake by plants. Nature 203:326-327.

5. Response of Crops Grown on Calcareous Soils to Fertilization

by

H. D. Fuehring
Agronomist
New Mexico State University
Plains Branch Station, Star Route, Clovis, U.S.A.

SUMMARY

Calcareous soils tend to be low in organic matter and available nitrogen. The high pH level results in unavailability of phosphate and sometimes zinc and iron. Potential productivity is very high where adequate nutrients and water can be supplied. Many of the calcareous soils under cultivation are irrigated and the irrigation water may supply crops with all the amounts needed for such elements as magnesium, potassium, sulphate, chloride and boron depending on the salt content of the water.

Nitrogen needs to be provided in line with the amount likely to be removed in the crop. Excessive nitrogen may be detrimental to some crops (sugarbeets for example). Where restricted layers in the soil prevent leaching of nitrate it may accumulate to amounts in excess of 600 kilograms per hectare in the root zone of crops. The recently developed nitrate electrode gives a means of easily and quickly analysing soil samples for nitrate. Ammonium or urea nitrogen may be lost from the surface of calcareous soils unless they are incorporated immediately. Ammonium fixation on the clay complex may tie up a considerable amount of applied fertilizer on newly irrigated desert soils.

Soil testing (sodium bicarbonate extraction) is probably the most practical means of determining the need for phosphorus fertilizer. Excess applied phosphorus may result in deficiency of zinc or iron. For calcareous soils, it is important that at least 60 percent of the applied phosphorus be in a water soluble form. Applied phosphorus is only partially taken up by crops the first year but the residue will be mostly taken up over a period of years. Thus, once the available soil phosphous has been brought to an adequate level, the long-term amount needed will be about in line with crop removal.

The recently developed DTPA extraction soil test for available zinc, iron, manganese and copper promises to be very good for determining the need for application of these nutrients to calcareous soils. Atomic absorption spectro-photometry greatly facilitates the determination of micronutrient cations as well as micronutrient cations. Zinc sulphate, broadcast and incorporated in the soil at 5 to 15 kilograms per hectare, is probably the most efficient method of supplying zinc for most crops. Soil applied iron has not been satisfactory on calcareous soils although use of polyphosphates as a carrier is promising. Heavy applications of animal manure may successfully prevent deficiency of iron and zinc if not too severe.

At high yield levels, various two and three-way interactions may -be important. At high plant population levels both zinc and boron are required in high amounts by maize. Applied sulphate and chloride tended to be detrimental to yields of both maize and sugarbeets due to negative P-S and P-Cl interactions. Sugarbeets in Lebanon gave considerable response to sodium but interactions with applied sulphate and chloride were negative. Thus, interaction effects were more important than the direct effects for yield of maize and sugarbeets. Central composite rotatable experimental designs offer a means of studying the interaction effects of several variables with a reasonable number of treatments,

5.1. Introduction

Soils containing free calcium carbonate develop from calcareous parent materials where weathering has not been intensive enough to remove all of the carbonate. Many of the soils in areas of arid or semiarid climates are calcareous and, in warmer regions, low in organic matter. The high pH levels result in relative unavailability of phosphorus and the micronutrients zinc and iron. Under irrigation, nitrogen is apt to be limiting. The physical condition of calcareous soils is usually satisfactory because the high calcium saturation of the cation exchange complex tends to keep them well aggregated.

Where adequate water and nutrients can be supplied, the inherent productivity of calcareous soils over large areas is excellent due to favourable growing season conditions. In the Bekaa Plain of Lebanon, yields obtained include 15.8 metric tons per hectare of maize grain, 148 metric tons per hectare of sugarbeet roots and nine metric tons per hectare of wheat grain. Although natural productivity is low, the potential productivity is very good. Therefore, the diagnosis of nutrient requirements and the supply of nutrients to crops in economic amounts is a problem of the first magnitude. The social problems of making the necessary information available to farmers, motivating them to use it and providing them with the means are being solved in the developing countries. This paper will be restricted to the state of knowledge regarding fertilizing of calcareous soils. Both deficiencies and excess of nutrients and salts occur and interactions among them may be of considerable importance.

5.2. Nitrogen Fertilization

Calcareous soils are usually somewhat low in organic matter and nitrogen is often the most limiting nutrient. For most crops nitrogen needs to be applied at rates from 1 to 1.5 times the anticipated removal in the crop less the amount estimated to be available in the soil. Where generous amounts of nitrogen have been applied in the past and where soils contain layers that impede leaching large amounts of nitrate may accumulate in the soil. The Holly Sugar Company in the Texas panhandle has found it necessary to test soils of prospective sugarbeet fields down to the 1 .2 metre level in order to restrict nitrogen levels to amounts unlikely to cause low sugar and impaired processing quality of the beets. Some fields were found to have more than 600 kilograms per hectare of nitrate nitrogen, an amount far in excess of that needed for sugarbeet production and resulting in low sucrose percentage beets with high impurities. Recently, the nitrate electrode has been developed and makes possible the simple and quick potentiometric determination of nitrate nitrogen by means of any pH meter equipped with a millivolt scale (Oien and Selmer-Olsen, 1969). An extracting solution containing 0.02 N copper sulphate and 3 ppm nitrate-N eliminates most interferences. This gives a method of keeping track of applied nitrogen and for determining the amount needed for the anticipated crop. More elaborate incubation methods are available but offer little additional information on calcareous soils with low organic matter. A recent method (Smith and Stanford, 1971) involving autoclaving for 16 hours offers considerable savings in time over incubation methods where it is desirable to determine potentially available nitrogen,

All forms of nitrogen fertilizer are microbially transformed into nitrate within a period of a few days during seasons of the year suitable for crop growth. Nitrate is mobile in the soil and moves readily with soil moisture making it subject to leaching in case of excessive rainfall or irrigating. Thus, nitrogen fertilizer may be applied any time from just before planting up to the time the plant is well established. Side-dressing to the growing crop is one of the most efficient ways of application. Nitrogen applied with or close to the seed may impede or prevent germination due to a salt effect. Nitrogen fertilizers are soluble salts or convert to soluble salts and thus may contribute to the salt problem in saline soils. Ordinarily the fertilizer salt would be a small part of the total salt and the main problem is to avoid concentration near the germinating seed. Where furrow irrigation is used, soil nitrate may move to the top of the ridges and accumulate as water evaporates. Here it may be relatively unavailable to plants unless washed down into the root zone by rainfall.

Ammonium nitrogen is held on the exchange complex of the soil and moves very little in this form. However, during warm weather, it is converted to nitrate. Ammonium nitrogen or forms such as urea which change to the ammonium form should not be left on the surface of calcareous soils (Terman and Hunt, 1964). The high pH and exposure at the surface will cause considerable loss of ammonia to the atmosphere by volatilization. Incorporation into the soil at time of application will prevent this.

Arid soils brought into cultivation may have a capacity to tie up several hundred kilograms of nitrogen per hectare as fixed ammonium on the clay complex (Mortland, 1966). Thus, considerable extra nitrogen may need to be applied during the first few years in order to saturate this requirement. Exclusive use of nitrate fertilizer would tend to get around this. More work is needed to determine the magnitude of the fixed ammonium problem and also on the subsequent availability of fixed ammonium under field conditions.

5.3. Phosphorus Fertilization

Calcareous soils are buffered to a pH level of 8.0 to 8.4 resulting in low availability of native soil phosphorus. Applied phosphorus quickly reverts to insoluble forms. Consequently little movement of applied phosphorus occurs. Olsen and Flowerdale (1971) have published a recent review on the subject of phosphorus in alkaline soils. Many efforts have been made to relate the phosphorus potential of the soil to phosphorus availability to crops. However, much work remains to be done since results vary for different crops at different levels of soil clays and organic matter. From a practical standpoint, the bicarbonate extractable form (Olsen et al. 1954) results in a reliable soil test showing both deficiency levels and levels of adequacy or possible excess. This test has given particularly good results in the alkaline pH range. The use of ascorbic acid as a reducing agent for forming the phosphomolybdic blue colour (Watanabe and Olsen, 1965) has increased the accuracy and ease of making the test.

In general, experimental results have shown that, to be effective on calcareous soils, applied phosphorus fertilizer should be at least 60 percent water soluble (Olsen and Flowerday, 1971). This would restrict application to monophosphates (ordinary or concentrated superphosphates) or polyphosphates which revert to monophosphates in the soil. Ammonium phosphates in which the phosphate remains mostly in the mono form would also be effective. Soluble phosphates are more effective when applied as granular rather than as finely divided material. The soluble monophosphate in the soil mostly precipitates rather quickly as the dicalcium phosphate. This precipitated phosphate has sufficient surface area to maintain a reasonably high level of soluble phosphate in the soil solution. This is in contrast to applied dicalcium phosphate which is relatively ineffective. While recovery of applied phosphorus is usually less than 20 percent during a single growing season, there is considerable residual effect and over a period of several years (Campbell, 1965) most of the applied phosphate can be recovered indicating a need for continuous monitoring of soil test levels. This also opens the possibility of applying heavy applications to last a number of years. However, there is a possibility of reducing availability of such nutrients as zinc and iron to deficiency levels for crops due to precipitation as insoluble phosphates at the pH levels of calcareous soils. Therefore, single heavy applications may not be practical both from the standpoint of effect on micronutrient availability and from the amount of capital tied up.

In the interest of minimizing the short term cost of production, band application of phosphate for row crops is about twice as effective as broadcast application in terms of crop response. However, this would result in less residual effect, so long-term savings would probably be negligible.

Amounts to apply depend on how deficient the soil is and also on how calcareous it is. Monk with sugarbeets (Fuehring and Hashimi, 1967) on a Lebanese soil containing 15 percent calcium carbonate showed increasing response up to 300 kilograms of P per hectare. However, rates above 73 kilograms were probably uneconomical considering only the first years return. Bates less than about 30 kilograms per hectare may not be practical since small increments sometimes result in no increase in yield or even a decrease. Time of application for most crops is before or at the time of seeding since phosphorus is needed most during the younger stages of growth.

5.4. Other Macronutrients

Irrigated calcareous soils are usually naturally well supplied with calcium, magnesium, potassium, sodium, sulphate and chloride depending somewhat on the salt content of the irrigation water. Analysis of irrigation water is essential in determining the supply of plant nutrients as well as for the salt balance of an irrigated area.

Under non-irrigated conditions or with very low salt irrigation water, deficiencies of sulphur may develop for some crops. Sandy soils may be deficient in potassium for some crops. Sodium may be somewhat deficient for crops such as sugarbeets which benefit from having adequate sodium.

5.5. Micronutrient Fertilization

The micronutrients zinc, iron, manganese and copper tend to be less available with increasing pH levels but the occurrence of deficiencies is highly erratic. The development of atomic absorption spectrophotometry in the past decade has greatly facilitated determination of the micronutrient cations. A recently developed soil test by Lindsay and co-workers (Lindsay, W.L. and Norvell, W.A. 1969). Development of a DTPA micronutrient soil test. Agronomy Abstracts), promises to be effective in defining areas of probable deficiency for these micronutrients. This test consists of extracting the soil with the chelating agent DTPA buffered at pH 7.3. Tentative deficiency levels have been established of 4.5 ppm for iron, 1.0 ppm for manganese, 0,5 ppm for zinc and 0.2 ppm for copper. However, work is still being conducted on the critical levels for various crops. In testing various soils from a calcareous sandy area producing chlorotic groundnuts, I picked out one that tested low in both zinc and iron for the site of a study on response of groundnuts to soil and foliar application of iron and zinc. However, very little chlorosis developed. It was then discovered that 25 tons per hectare of barnyard manure had been applied the year previously. Apparently the manure tended to correct the deficiencies without appreciably affecting the soil test results. The soil test gave erroneous results under these conditions.

Deficiencies of these micronutrients result in chlorosis of varying severity. The deficiency symptoms are sometimes helpful in diagnosis but often they are complicated by multiple deficiencies or by infestation of insects or disease. It is possible to have considerable response to zinc when check plots show no noticeable deficiency symptoms.

Zinc deficiency is probably most pronounced in maize especially at high population levels. Relatively small amounts of zinc are required. Zinc sulphate is effective and is the form usually used, since it is relatively inexpensive. Foliar applications or dormant sprays are usually used on fruit trees. For soil application, six to eight kilograms of actual zinc per hectare broadcasted and incorporated are usually sufficient although maize on a highly calcareous soil may respond up to 90 kilograms per hectare (Fuehring et al. 1969b). One application is usually sufficient for several years because zinc does not leach or move appreciably in the soil. Use of chelated zinc will reduce the amount needed by a factor of from about two to five. Chelated zinc is more expensive and the residual effect would be less.

Plant tissue analysis has been used to diagnose zinc deficiency in fruit trees, maize, sugarbeets, etc. However, levels vary with age of and type of tissue and also depends on the balance with other elements.

Iron deficiency shows up as interveinal chlorosis of leaves and is more difficult to correct than zinc deficiency since soil application results in rapid reversion to unavailable forms. Some plant species, sorghum for example, are more susceptible to iron deficiency than others. One method of overcoming it is to avoid using susceptible crops. Foliar sprays with ferrous sulphate will result in greening of foliage but the effect is usually only temporary. Chelated iron is more effective for soil application than inorganic forms but at the pH of calcareous soils most chelates are unstable. Geigy's chelate 138 is stable in calcareous soils but is expensive to use. Mortvedt and Giordano (1971) have been working to find practical ways of applying iron in calcareous soils, but much more work is needed. They have had some success with fluid polyphosphate mixtures as carriers of iron. Field application requires considerably more work in that the amount of iron that can be carried is limited by its solubility in the mixture. Also more phosphate than required may have to be applied in order to get sufficient iron.

Manganese and copper are much less apt to be deficient on calcareous soils than iron and zinc. If deficient the sulphate forms are commonly applied to the soil. Many soils have large amounts of available manganese and copper which may tend to upset the balance with iron and zinc. Addition of manganese or copper should be avoided where soil test levels indicate more than adequate amounts already present.

Some calcareous soils may be deficient in boron. However, many irrigation waters carry considerable boron. With high boron irrigation water toxicity to plants may be a problem as boron accumulates. Since the margin between boron deficiency and toxicity is rather narrow, caution is needed to get uniform distribution in the soil and to avoid a boron build-up through repeated application. Hot water soluble boron is the most common soil test used. Crops susceptible to boron deficiency include alfalfa, sugarbeets and corn at high plant population levels. Areas where the irrigation water contains more than 0.1 ppm boron will probably have enough for most crops. Wilcox and Durum (1967) give a list of crops with increasing sensitivity to boron toxicity from 4 ppm down to 0.3 ppm boron in the irrigation water.

5.6. Organic Materials as Fertilizers and Soil Amendments

The use of organic wastes as fertilizers is very ancient since it not only replaces nutrients in the soil but also disposes of a polutant. However, in the developed countries at least, the use of commercial chemical fertilisers offers considerable advantages in the form of ease and precision of application. The cost of handling bulky organic materials such as barnyard manure tends to be greater than the cost of applying needed nutrients through concentrated chemical fertilizers. However, since the organic waste material must be disposed of, application to the land is a good way of utilization as long as human wastes do not constitute a disease problem.

Organic materials as fertilizers have the advantage of being slow-release sources of nutrients which also tend to be balanced. Alternative uses as feed or fuel may preclude use as fertilizer in many parts of the world.

Plants take up practically all nutrients in the inorganic form which means that organic sources must first be broken down before plants can use them. There is no definite evidence that food grown with strictly organic fertilizer sources is more nutritious or more flavoured.

Most calcareous soils are naturally low in organic matter and a build-up of organic matter would tend to buffer them from the standpoint of nutrient sufficiency as well as the physical condition of the soil. The residues (stems, leaves, roots, etc.) of most high yielding crops will tend to build up soil organic matter if left in the field. However, the organic matter level in the soil tends to equilibrate with climatic conditions as well as cultural practices. In hot climates, biological activity in the soil is very great and organic material breaks down rapidly. So organic matter build up in the soil is not an efficient process since .much of it tends to be rapidly decomposed. Also, especially in the initial rapid breakdown, substances toxic to seed germination and plant growth may be released and temporarily inhibit or impede crop growth. Crop residues low in nitrogen and incorporated into the soil will result in a tie-up of soil N as the micro-organisms expand rapidly in numbers and mass and utilize all available N. Large amounts of bulky organic residues may impede cultivation and seeding practices.

The use of organic material to alleviate a poor physical condition in the soil may be important in some cases. Calcareous soils tend to be well aggregated and soil structure is usually good. Where topsoil has been removed in land levelling to improve surface irrigation, yields are often very poor due to lack of available nitrogen, phosphorus, zinc and sometimes iron. The physical condition may also be poor due to compacting during levelling. Adding large amounts of commercial fertilizer will partially correct the adverse conditions but considerable expense is involved. Adding large quantities of livestock manure and working it into the surface soil is effective in alleviating the condition but often manure is not available. Probably the best way of avoiding trouble from land levelling is to arrange operations so that 15 to 20 cm of the topsoil is stockpiled and then returned after the grade has been established. While this may double the cost of levelling, improved yields the first year or two will probably more than pay the extra cost. Soils with reasonable amounts of organic matter (more than 15%) in the topsoil would be most affected by removal while soils with low organic matter (less than about 0,3% as in desert soils) would probably not be appreciably affected.

A build-up of organic matter in soils is sometimes advocated in order to enhance the water holding capacity. This would be of very minor importance in most soils since the probable increase in available water holding capacity would be in the order of one or two percent at most.

Heavy rates of barnyard manure applied to the soil may be a means of alleviating deficiencies of micronutrients such as iron and zinc which may be severely lacking in availability in some calcareous soils.

Use of organic materials as fertilizers depends on a number of economic factors. Alternative means of utilizing or disposing of the materials and alternative sources of plant nutrients are important factors. Calcareous soils are usually well aggregated so problems related to poor soil structure are usually not very important.

5.7. An Experimental Design for Plant Nutrition Studies

As crop yields are pushed up toward theoretical maxima, the supply of nutrients becomes more of a problem not only directly hat as interaction effects between or among two or more elements. Conventional factorial experimental designs allow determination of these effects, hut as the number of levels and factors studied is increased the number of plots required rapidly becomes unwieldy. The use of rotatable central composite designs (Cochran and Cox, 1957) is one means of compromising. A complete two-level factoria consists of 16 points for four variables, 32 for five, and 64 for six. A central point at the middle level of each variable and additional very high and very low points are added making five levels for each variable. For four variables this would make 25 treatments. For exploratory work, the treatment with all variables at the middle of five levels is repeated seven times resulting in six degrees of freedom for error and a total of 31 plots. For more precise experimental work, the whole set of 25 treatments can be replicated two or more times. I find that two replications of the four variable design giving a total of 50 plots and 24 degrees of freedom for error results in a workable size experiment. Cochran and Cox (1957) give five and six variable versions of the design using one-half of a complete factorial for the two main levels. However, the three-way interactions are confounded when this is done. I have found the three-way effects to be more important than the direct or two-way effects in many cases so I believe a complete two-level factoria should be adhered to even at the expense of using a greater number of treatments. The five levels can be set on an arithmetic scale if the area of probable response can be somewhat approximated on a relatively narrow range of values used. Where a wider range may be desirable, as with micronutrients, a logarithmic scale can be used. A logarithmic scale to the base two (doubling the rate at each step) will cover a fairly wide range. A disadvantage of the log scale is that a zero rate is never attained. In order to facilitate calculations and interpretation the levels are coded on a scale of -2, -1, 0, +1 and +2 with the extremes varied somewhat from this according to the number of variables involved. The variables can involve any factors that can be set qualitatively such as applied nutrient levels, plant population density and irrigation interval.

The data is analysed in the form of a quadratic regression equation by determining the statistical significance of the individual regression coefficients. Use of a computer greatly simplifies the calculations once they have been programmed. The equation can be solved for the combination of variables resulting in maximum yield and when plant analysis is used in conjunction with the experiment, critical levels of nutrients in various plant tissues at various stages of growth can he determined.

5.8. Plant Nutrient Interaction in Maize

Work in the Bekaa Plain of Lebanon during the 1960's (Fuehring et al. 1969b) resulted in maize grain yields up to 15.8 metric teas per hectare, about an high as anywhere in the world. In a series of eight irrigated field experiments yields required high levels of plant population and applied nitrogen, phosphorus, zinc and boron. Levels of applied sulphate and chloride needed to be low (Figure 1). Usual rates of application for N, P, S, and Cl were 37, 75, 150,300 and 600 kg/ha which were coded as -2, -1, 0, +1, and +2 respectively. Corresponding rates for Zn, Mn, and B were 11, 22, 45, 90 and 180 kg/ha. Plant population was varied from 40 to 93 thousand plants/ha. Fertilizers were applied at seeding time in a broad band about 5 cm below the seeds. It was found that high rates of N and P (around 300 kilograms of each per hectare) were required for maximum yields. The N levels are la line with I removal in the harvested crops but P is far in excess of that removed and most of the applied P remained in the soil. It would appear that relatively heavy initial applications were necessary on these calcareous soils (around 15% CaCO3) but subsequent applications could be reduced in line with the amounts needed to keep soil test levels at an adequate level. This is an area where much more work is needed.

Figure 1. Yield of maize grain (from regression equation) as affected by plant population (POP) and application of Zn, P, N, B, Mn, Cl, and S in a series of eight experiments. When not varied, plant population, Zn, P, N, and B were held at high levels and Mn, Cl, and S at low levels.

The amount of P fertiliser to be applied for maximum yields of maize varies from around 300 kilograms per hectare on a 15% CaCO3 soil in Lebanon to about 30 kilograms per hectare on a nearly neutral soil on the High Plains of eastern New Mexico where amounts in excess of 30 kilograms were found to have an increasingly depressing effect on grain yield of maize. The long-range requirement of fertilizer P would probably be the same but it would have to be applied at more frequent intervals on non-calcareous soils.

In three out of four experiments in Lebanon, there were relatively large negative P-S interactions. The P-Cl interaction was negative in all three of the experiments where it was present. Thus, high rates of either sulphate or chloride tended to negate the positive response to phosphorus. The N-P-S three-way interaction was negative and of considerable magnitude indicating that sulphur needed to be kept low at the necessary high levels of nitrogen and phosphorus. Under saline conditions or with high salt irrigation water it My not be possible to keep sulphate and chloride low enough to obtain very high yield levels.

Humorous reports in the literature (Stukenholtz et al. 1966) indicate a positive P-Zn interaction with excessive applied phosphorus resulting in or intensifying the deficiency of zinc. The effect appeared to take place in the plant roots rather than in the soil. The work in Lebanon resulted in both negative and positive P-Zn interactions with no definite effect apparent.

Work in the greenhouse (Koukoulakis, 1967) using two calcareous soils from Lebanon resulted in greater zinc availability to maize plants grown in the more calcareous of the two soils (33% CaCO3 vs 14%). It was found that the roots of the plants grown in the ore highly calcareous soil had ore calcium, as expected, and about the same level of phosphorus (Table 1). However, less phosphorus was translocated to the plant tops indicating a tie up of phosphorus in the roots, probably with calcium. The plants grown in the more calcareous soil had less zinc and manganese in the roots and a higher concentration of the two in the tops. It was postulated that the phosphorus in the roots of the plants grown on the less calcareous soil was more active (less tied up by calcium) and tended to hold the zinc and manganese in a less active form, thus tending to prevent translocation of zinc and manganese to the tops. Thus, the excess calcium of calcareous soils reacts with phosphorus directly in plant roots and indirectly affects the translocation of micronutrients from roots to tops.

Figure 2. Effect of negative N-B-S interaction on yield of maize grain (from regression equation).

Table 1. Composition of greenhouse-grown maize plants. American University of Beirut. 1967.

Maize Plants

Soil 1
14% Lime

Soil 2
33% Lime

P, %Tops

.251

.155


Roots

.208

.219

Ca, % Tops

.5

1.3


Roots

3.6

7.7

Zn, ppm, Tops

32

61


Roots

177

117

Mm, ppm, Tops

56

72


Roots

453

170


In the Lebanon studies, maize responded to zinc and boron at rates up to 90 kilograms per hectare especially as the plant population level was increased. The Zn-B-plant population interaction was positive in All three experiments in which it appeared indicating increasing need for all three as the yield level is pushed up. The P-B-population three-way interaction was also positive. On a non-calcareous soil in New Mexico, the N-Zn-B interaction was positive far grain yield. However, the optimum levels required were in the order of six kilograms per hectare for zinc and three for boron, an order of magnitude smaller than on the calcareous soil. It appears that maize has high requirements for both zinc and boron as plant population and yield levels are increased.

5.9. Plant nutrient Interaction in Sugarbeets

Fuehring et al. (1969a) summarized the results of 13 multivariate field experiments conducted from 1960 to 1966 in the Bekaa Plain of Lebanon. Yields of sugarbeets were obtained as high or higher than anywhere in the world. Yields up to 25 metric tons of sucrose compare favourably on an annual basis with yields obtained for sugar cane in Hawaii. In general, high rates of applied nitrogen, phosphorus and sodium were necessary along with low levels of sulphate, chloride, zinc and boron. The interaction effects tended to be more important than the direct effects except for the rather large positive direct effect of nitrogen on yield. The Na-S and Na-Cl interactions were negative indicating a need to keep sulphate and chloride levels low in order to get maximum response to applied sodium. Thus, sodium chloride and sodium sulphate would be poor sources of sodium. Sodium nitrate would probably be the best source of sodium as long as the total supply of nitrogen is adjusted to the amount required. The response to sodium would depend on the supply in the soil and particularly on the level in the irrigation water. Water with more than one milliequivalent per litre would probably have sufficient sodium. The response to applied sodium was maximized at the rate of 130 kilograms per hectare with irrigation water having 0.28 milliequivalents per litre of sodium. Petiole analysis (Fuehring and Hashimi, 1967) indicated a critical level of around two percent early in the season tapering off to around one percent near the end of the growing season. Excess sodium tended to decrease yields so a soil, water and plant petiole analysis is necessary to determine whether additional sodium would be beneficial to yields.

Figure 3. Yield of sucrose from sugarbeets (from regression equation) as affected by applied N, Na, P, K, sulphate, Mg, B, Zn, and chloride in a series of 13 experiments. When not varied, N, Na, P, and K were held at high levels and sulphate, Mg, B, Zn, and chloride were held at low levels.

Figure 4. Effect of applied sodium on yield of sucrose and sodium concentration in petioles.

Nitrogen at the rate of 150 kilograms per hectare (Fuehring and Hashimi, 1967), was enough for nearly maximum yields of sugar. These were on fields that had been fallow the previous year and presumedly had accumulated considerable available nitrogen. Work in the United States has determined that it takes about 10 pounds of nitrogen for each ton of sugarbeets produced. Thus, if the amount of nitrate-N accumulated in the profile is known and the probable attainable yield level is known, the amount of fertilizer N required can be determined roughly by difference. The critical level of nitrate-N in the sugarbeet petioles was found to vary from around 4 000 ppm at 60 days after planting to about 300 ppm at 180 days after planting (Fuehring and Hashimi, 1967).

In general, yield of sucrose increased as phosphorus application was increased up to 300 kilograms per hectare. Since there is much more phosphorus than actually used, the balance would be carried over and could be used by subsequent crops. Periodic soil testing would be necessary in order to monitor the available phosphorus levels in soils and to determine when additional phosphorus would be required.

Figure 5. Effect of applied nitrogen on yield of sucrose and nitrated concentration of petioles.

Figure 6. Effect of applied phosphors on yield of sucrose and phosphate-P concentration of petioles.

In general, the high boron and zinc levels necessary for high corn yields tended to decrease yields of sugarbeets. The N-Na-Zn three-way interaction was negative and of considerable magnitude so, with nitrogen and sodium at high levels, zinc would have a depressing effect on yield. Zinc also had important interactions with nitrogen (negative) and chloride (positive) which contributed to its general depressing effect. The linear effect of boron was consistantly negative and accounted for much of the net negative effect of applied boron on sucrose yields.

Figure 7. Effect of negative N-Na-Zn interaction on yield of sucrose of sugarbeets (from regression equation).

The general depressing effect of sulphate and chloride on yields of both maize and sugarbeets is probably associated with the cation-anion balance in plant tissues. Noggle (1966) found that the greater the proportion of organic anions (difference between total cations and total anions on an equivalent base) in plant tissues, the greater the yield for a number of species.

5.10. Response of Cotton to Fertilizers

Luckhardt and Ensminger (1968) gave a comprehensive review of fertilizer use on cotton. The nitrogen requirement of a cotton crop amounts to about 60 lb. per bale of lint produced so the amount to be applied depends mostly on the probable yield level with allowances for amounts present in the soil profile (soil test for nitrate-N). Thus, high yielding cotton (5 bales per acre) may respond up to 400 lb. of applied N per acre where original amounts available in the soil are low. Excess nitrogen tends to delay flowering and should be avoided. On sandy soils at least part of the nitrogen should be applied as an early sidedressing. Cotton is sensitive to phosphorus deficiencies especially during the boll forming stage and phosphorus should be added according to soil test. Initial requirement is low so sidedressing up to time of first bloom is effective. Potassium should be applied if soil tests are low (less than 60 ppm on sandy soils to 100 ppm on fine textured soils) but most calcareous soils have adequate K levels. Zinc and iron may be deficient for cotton on some calcareous soils and can be remedied with spray applications.

Plant tissue analysis at time of initial bloom allows addition of nutrients before the time of maximum uptake about 43 days later. It the early bloom stage 18 to 20 thousand ppm nitrate N in the petioles of the youngest mature leaves may be necessary in order to maintain nitrogen above the 2 000 ppm critical level throughout the growing period. The phosphorus critical level in petioles is 1 000 ppm and is relatively stable throughout the season. A value of 3 500 ppm total phosphorus in leaf blades has also been used as the critical level. The critical level for potassium in leaf petioles is 4 to 5% at first bloom dropping to about 2% late in the season.

5.11. Response of Alfalfa to Fertilizers

Wagner and Jones (1968) have reviewed the literature on fertilization of high yielding forage crops. High yields of alfalfa (6 to 10 tons per acre) remove large quantities of nutrients from the land and long time intensive cropping will result in considerable need for phosphorus (70 to 120 lb. P2O5 removed per acre per year) and possibly potassium (250 to 500 lb. K2O removed per acre per year). Soil tests are the best indicators of initial P and X levels. Where deficient levels are indicated, fairly large amounts are usually added initially in order to build up to adequate levels with maintenance amounts added thereafter. The time and method of adding the maintenance amounts is relatively unimportant as long as distribution is uniform. High yielding non legume forage crops would require similar amounts of phosphorus and potassium along with large amounts of nitrogen (up to 800 lb. per acre).

5.12. Response of Olives to Fertilization

Olives are often grown on soils unsuitable for other crops and low in nutrients and thus usually respond well to application of fertilizers. De Geus (1967) has reviewed the fertilisation of olives. When nutrients are short, olive trees may be thrown into bearing alternate years being unable to produce both fruit and the new growth necessary for the next years crop. Olives retain their leaves for three years and during this time they serve as a storehouse of nutrients decreasing during fruit filling and increasing at other times of the year. Foliar analysis is used but the time of year and age and location of leaves sampled must be carefully defined. Critical levels for nitrogen in leaves have been given of from 1.2% (California) to 1.75% (high yielding trees in Tunisia). The phosphorus critical level is around 0.10 to 0.15% and the potassium critical level varies from 0.8 to 1.2% the higher figure needed on more calcareous soils and at higher yield levels. The foliage sampled is from flower bearing twigs during spring or during winter when levels are relatively stable.

Levels of fertilizer recommended for high yielding olive trees (200 lb. or more) are 1 to 2 lb. N, 1/3 to 2/3 lb. P, and 1 to 2 lb. K. Under irrigation and very high yields (400 lb. per tree) doubling of these amounts may be necessary. Continued application over a period of years may result in an accumulation of P and K in the soil. Foliar analysis gives a way of monitoring nutrient levels over a period of time. In order to insure adequate fruit set the fertilizer should be applied some time prior to flower initiation. Placement should be in the root zone and deep enough to prevent soil drying out. Concentrating P in a band or in a few places around the tree will tend to prevent rapid fixation of P into unavailable forms. .On the more fine textured soils, soil K may be adequate and fertilizer K unnecessary. A soil test would be in order under these circumstances.

5.13. Response of Citrus to Fertilization

Fertilizer use on citrus has been reviewed extensively by Reitz and Stiles (1968) and De Geus (1967). Nitrogen is usually the most limiting nutrient factor. Leaf analysis is probably the best way of monitoring the levels of nutrient available as well as the balance among nutrients. Soil analysis values are less effective because of the difficulty of securing samples representative of the entire zone from which roots draw nutrients. Non-uniform placement of previous fertilizer applications is also a factor. An initial soil test before establishment of the citrus grove may have considerable value with regard to phosphorus levels. Chapman's (1960) leaf analysis values (4 to 7 months old spring cycle from fruit bearing terminals) consistent with top performance are probably the ones most pertinent to citrus grown on calcareous soils. Values given are (in percent of dry matter) 5.0 Ca, 0.4 Mg, 1.0 K, 2.4 N, 0.12 P, 0.30 S, 0.05 Cl and (in ppm) 75 B, 5 Cu, 60 Fe, 35 Mn, 0.20 Mo and 25 Zn. The values for the following (in ppm of dry matter) should be less than 0.05 As, 100 Br, 0.10 Cr, 20 F, 0.50 Li, 0.40 Co and 0.40 Ni.

High yielding oranges may respond in yield up to 300 to 400 lb. per acre of applied N. However, where colour is important, as with oranges sold as fresh fruit, excessive N may result in green coloured fruit. Zinc and iron if needed are usually applied as foliar sprays.

5.14. Response of Vegetable Crops to Fertilization

Since vegetables are high value crops used directly as human food adequate fertilizer application usually constitutes a small part of the total cost of production. Lorenz and Bartz (1968) hove reviewed fertilization practices needed for production of vegetables. Amounts of phosphorus and potassium are applied at rates high enough to bring soil test levels up to high levels. Nitrogen should be applied at rates somewhat greater than the anticipated amount found in the crop at time of harvest.

A study in Lebanon (Fuehring, 1969) on fertilizing and irrigation of tomatoes on calcareous soil indicated a need for a balance of applied N, P and S in order to decrease the cracking of Big Boy tomatoes. Irrigations could be made at less frequent intervals when N, P and S were in balance. While S had little influence on total yield, it increased marketable yield by reducing cracking. However, a variety more resistant to cracking would probably not show the response to S. Work by Zarei (1966) in Lebanon indicated split application of N (at initial fruit set and 45 day later) to be superior to applying all N at time of transplanting. There was also considerable positive' response to Zn application where the X application was split.

A series of field experiments on potatoes (Fuehring and Ghurrayyib, 1969) on a calcareous soil in Lebanon indicated response to I, P and K at high levels (300 kg of each per ha), and Mg at levels around 150 kg per ha. In general, S, Cl and Zn resulted in yield decreases. The K and Mg response was chiefly the remit of negative interactions with S and Cl.

5.15. Cropping Systems and Maintenance of Soil Fertility

Cropping systems to be used depend on numerous economic as well as agronomic factors. Where two or more crops are needed and can be grown in an area, rotation of crops from year to year offers several advantages such as control of diseases, weeds, insects and nematodes. Crops with different rooting patterns tend to vary the areas of nutrient extraction from the soil. Some crops (such as maize or fruit trees) do well under monoculture while others (sugarbeets) run into difficulties. Adequate fertilizer application tends to overcome nutritional aspects of monoculture but this implies availability and use of soil testing facilities. Legume forage crops will provide livestock: feed as well as build up soil nitrogen supplies. The feasibility of their use depends on having a use for the produced forage as well as the availability of an alternate source of nitrogen. Legume seed crops do little to build up soil nitrogen although they will need no applied N if the proper rhizobium are present either by inoculation of the seed or presence in the soil from previous crops.

The use of fallowing as a means of increasing available soil N (through breakdown of soil organic matter during the fallow period) tends to decrease the level of soil organic matter over a period of time and is a wasteful use of land. However, if land is more plentiful than water and if fertilizer N is not available, fallowing offers a means of increasing water use efficiency, in the short run at least.

The use of green manure crops to be incorporated into the soil will tend to concentrate available nutrients for the next crop but is wasteful of water in that no direct benefit is derived.

The use of improved varieties of crops is essential in utilizing high levels of fertility. The recently developed short-statured small grain varieties can produce high yields of grain in the presence of plentiful soil nitrogen without becoming severely lodged. Also, the potential of new crop varieties cannot be realized unless the required plant nutrients are also made available.

In general, fertilizing and other practices resulting in high yielding crops will tend to conserve and build up fertility levels in the soil especially as crop residues are retained on the soil.

REFERENCES

Campbell, R.E. 1965, Phosphorus fertilizer residual effects on irrigated rotations. Soil Sci. Soc. Amer. Proc. 29:67-70.

Chapman, H.D. 1960, Leaf and soil analysis in citrus orchards. Criteria for the diagnosis of nutrient status and guidance of fertilization and soil management practices. Univ. of California, Division of Agr. Sciences, Manual 25.

Cochran, W.G. and Cox, C.M. 1957, Experimental designs. 2nd ed., John Wiley and Sons, Inc., New York.

De Geus, J.G. 1967, Fertilizer guide for tropical and subtropical farming. Centre d'Etude de l'Azote. Zurich, Switzerland.

Fuehring, H.D. 1969, Yield and degree of cracking of Big Boy tomatoes as affected by application of nitrogen, phosphorus and sulphur and by frequency of irrigation. Mimeo Pamphlet No. S.I. 1, Soils and Irrigation Division, Faculty of Agricultural Sciences, American University of Beirut, Beirut, Lebanon.

Fuehring, H.D. and Ghurayyib, A.A. 1969, Fertilizers for irrigated potatoes in the Bekaa Plain of Lebanon. Faculty of Agricultural Sciences Publication No. 36, American University of Beirut, Beirut, Lebanon.

Fuehring, H.D. and Hashimi, M.A. 1967, Foliar analysis in the nutrition of sugarbeets. In T.S. Stickley et al. (ed.) Man, food and agriculture in the Middle East. American University of Beirut, Beirut, Lebanon.

Fuehring, H.D. Hashimi, M.A. Haddad, K.S., Hussieni, K.K. and Makhdoom, M.U. 1969, Nutrient interaction effects on sucruse yield of sugarbeets on a calcareous soil. Soil Sci. Soc. Amer. Proc. 33:718-721.

Fuehring, H.D., Mirreh, H.P., Nazir Ahmad and Soltanpour, P.N. 1969, Grain yield of maize in relation to nitrogen, phosphorus, sulphate, chloride, zinc, boron, manganese, and plant population. Soil Sci. Soc. Amer. Proc. 33:721-724.

Koukoulakis, Prodromos. 1967, Zinc phosphorus nitrogen interrelationships in maize nutrition. M.S. theses, Faculty of Agricultural Sciences, American University of Beirut, Beirut, Lebanon.

Lorenz, O.A. and Bartz, J.F. 1968, Fertilization for high yields and quality of vegetable crops. In L.B. Nelson et al. (ed.) Changing Patterns in fertilizer use. Soil Sci. Soc. Amer. Madison, Wis.

Luckhardt, R.L. and Ensminger, L.E. 1968, Fertilizer use on cotton. In L.B. Nelson et al. (ed.) Changing Patterns in fertilizer use. Soil Sci. Soc. Amer. Madison, His.

Mortland, M.M. 1966, Ammonia interactions with soil minerals, p. 188-197. In M.H. McVickar et al. (ed.) Agricultural anhydrous ammonia technology and use. American Society of Agronomy, Madison, Wis.

Mortvedt, J.J. and Giordano, P.M. 1971, Response of grain sorghum to iron sources applied alone or in fertilizers. Agron. J. 63:758-761.

Noggle, J.C. 1966, Ionic balance and growth of sixteen plant species. Soil Sci. Soc. Amer. Proc. 30:763-766.

Oien, A. and Selmer-Olsen, A.R. 1969, Nitrate determination in soil extracts with the nitrate electrode. Analyst 94:88-894.

Olsen, S.R., Cole, C.V., Watanabe, F.S, and Dean, L.A. 1954, Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Cir. 939.

Olsen, S.R. and Flowerday, A.D. 1971, Fertilizer phosphorus interactions in alkaline soils. In R.A. Olsen et al, (ed.) Fertilizer technology and use. 2nd ed., Soil Sci. Soc. Amer., Madison, Wis.

Reitz, H.J. and Stiles, W.C. 1968, Fertilization of high producing orchards. In L.B. Nelson et al. (ed.) Changing Patterns in fertilizer use. Soil Sci. Soc. Amer., Madison, Wis.

Smith, S.R. and Stanford, G. 1971, Evaluation of a chemical index of soil nitrogen availability. Soil Sci. 111:228-232.

Stukenholtz, D.D., Olson, R.J., Gogen, G. and Olson, R.A. 1966, On the mechanism of phosphorus zinc interaction in corn nutrition. Soil Sci. Soc. Amer. Proc. 30:759-763.

Terman, G.L. and Hunt C.M. 1964, Volatilization losses of nitrogen from surface applied fertilizers as measured by crop response. Soil Sci. Soc. Amer. Proc. 28:667-672.

Wagner, R.E. and Jones, M.B. 1968, Fertilization of high yielding forage crops. In L.B. Nelson et al. (ed.) Changing Patterns in fertilizer use. Soil Sci. Soc. Amer., Madison, Wis.

Watanabe, F.S. and Olsen, S.R. 1965, Test of an ascorbic acid method for determining phosphorus in water and NaHCO3 extracts from soil. Soil Sci. Soc. Amer. Proc. 29:677-678.

Wilcox, L.V. and Durum, W.H. 1967, Quality of irrigation water. p. 112, In Hagen et al. (ed.) Irrigation of agricultural lands. Amer. Soc. Agron., Madison, Wis.

Zarei, Faramarz. 1966, Yields, fruit cracking and leaf composition of tomatoes as affected by mineral nutrition. M.S. thesis, Faculty of Agricultural Sciences, American University of Beirut, Beirut, Lebanon.

6. Some Physical Properties of Highly Calcareous Soils and their Related Management Practices

by

Fathy I. Massoud
Technical Officer
Soil Resources Development and Conservation Service
Land and Water Development Division, FAO, Rome

SUMMARY

The paper presents some physical properties of the highly calcareous soils and the related management practices. The true evaluation of their texture must take into account the inherent particle size distribution of the CaCO3 which can be found in various size ranges. Generally, in a fine textured soil most of the CaCO3 is within the clay and silt fractions. The highly calcareous soils, regardless of their texture, have the sane moisture depletion pattern and this entails frequent irrigation. It has been found that by following the right irrigation regime, it was possible to double the dry weight of maize plants. The increase in CaCO3 content, especially above 35% has adversely affected the vegetative growth of maize plants.

The diffusivity of water through calcareous soils was found to be higher than through non-calcareous soils of similar texture. Increasing CaCO3 up to 10 or 15% increased diffusivity while a further increase up to 20 or 25% relatively reduced it. In highly calcareous soils, it seem that the size distribution of the carbonate had more effect on diffusivity than did its total content. A study on infiltration and redistribution of water in a highly calcareous soil is presented to show the moisture profile development during redistribution, its relation to the F.C. concept and its importance to the water storage capacity of the soil.

Soil crusting is discussed in relation to the moisture regime effect on seedling emergence and factors affecting its strength. Heavy water applications delayed crusting but produced a thicker crust. The most apparent feature of the crust is its higher bulk density than the subcrust. A high rate and percentage of emergence could be obtained if the moisture tension of the crust is kept relatively low and the right planting technique and depth of seeding are followed. The relative importance of the factors affecting crust strength follow the sequence, bulk density > moisture tension > silt > silt + clay > sand > clay > CaCO3.

Experiments are presented to show that the tilth of these highly calcareous soils could be affected by the use of different tillage implements and techniques. Selecting the right plough, depth of ploughing and the optimum moisture content at time of ploughing have Improved the soil tilth.

6.1. Introduction

Calcareous soils are of wide occurrence in the Near East Region, under arid and semiarid climates, where the presence of CaCO3 in considerable amounts, sometimes above 20 percent, is not uncommon. Kadry (1972). High CaCO3 content, especially the active fraction, affects the chemical characteristics of the soil, its fertility and its physical properties. The author, while working in the Soils and Water Department, Faculty of Agriculture and the Land Reclamation and Improvement Institute of the University of Alexandria, had the chance to study some of the physical properties of the highly calcareous soils of the north-western region of Egypt. It is the purpose of this paper to present and discuss some of these properties and the practical management practices that could be applied.

6.2. Particle Size Distribution

Particle size determination is being carried out in most of the soils laboratories as routine work. Not only the relative proportions of the different size fractions can be obtained from this determination, but also some other physical and chemical characteristics can be deduced.

It is common practice during the pretreatment of mineral soils to remove all their CaCO3, but such a practice is questionable for highly calcareous soils where the calcium carbonate is found not only as a cementing agent but also as a distinct component of the mineralogical composition of the soil in various size ranges. This inherent particle size distribution has to be taken into account to obtain a true evaluation of the soil texture.

If the CaCO3 is retained, the particle size distribution obtained will depend on the dispersion technique and, therefore, the selected technique may be said to define arbitrarily the mechanical composition. Day (1965) reported that mixtures of NaPO3 and Na2CO3 have proved particularly effective as a dispersing agent and have made it possible to disperse calcareous soils without the prior removal of alkaline earth carbonates. The optimal concentration of the dispersing agent is best determined by preliminary tests. Concentrations of 0.010, 0.015, 0.20 N of sodium hexametaphosphate were tried in the final suspension and the results indicated that in this concentration range, no more dispersion occurred by increasing the concentration of the dispersing agent above 0.01 N, Salim and Massoud (1966). Dispersion of calcareous soils can be obtained by ultra-sonic vibration techniques, Watson (1971).

The inclusion of CaCO3 in the respective fractions, without considering its own size distribution, may lead to a misleading interpretation of the behaviour of highly calcareous soils when such interpretation is based on particle size distribution alone. For example, the minute silicate colloidal particles are accompanied by a tremendous number of adsorbed cations, while CaCO3 particles of the same size are not. Likewise, the presence of very fine particles of CaCO3 is believed to be responsible for the chlorosis of many crops which may not occur if these particles are made up of clay minerals. Similarly, a trained soil surveyor may find it difficult when using the feel method, to match the texture of a highly calcareous soil found in the field with that of the laboratory, since both methods are influenced by the high CaCO3 content of the soil; his estimate would be rather erroneous if the CaCO3 had been removed. Therefore, for highly calcareous soils it is desirable to complement the particle size distribution of the soil with that of its CaCO3.

The determination of particle size distribution, of CaCO3 can be achieved by analysis of the whole soil sample with and without removal of its lime content. For a given size fraction the difference between these two analyses gives the amount of CaCO3, present in that size range. The same value could be obtained by determining the CaCO3 content in a given size fraction taken without prior removal of the soils carbonates. Moreover, the determination of the very fine fraction of CaCO3 in the silt and clay size range, which is a measure of the potentiality of calcareous soils to cause chlorosis (active lime), can be achieved by adsorption methods, Drouineau (1942), Yaalon (1957).

The significance of knowing particle size distribution, both with and without removal of CaCO3, can be recognized from analysis of the data reported by Menon (1971) on the soils of the Ghab project in Syria, given in Table 1.

Table 1. Soil Particle and CaCO3 Equivalent Size Distribution of Pilot Area, Ghab Project, Syria




Clay

Silt

Sand

CaCO3


<0.002 mm

0.05-0.002 mm

0.05-2.0 mm

%

%

%

%

Before removing carbonates

28

43

29


After removing carbonates

9

11

12

68

Distribution of carbonates

19

32

17


% loss due to removing carbonates

68

74

60


Distribution of carbonates as percent of total CaCO3 equivalent

28

47

25



The data show that the texture of such soils would be clay loam if determined in the laboratory without removing CaCO3, although the clay and silt fractions are those usually found in a non-calcareous loamy sand or sandy soils. The same soil would probably be classified as silt clay by a soil surveyor in the field. To avoid such confusion and a misleading interpretation, data on particle size distribution of calcareous soils ought to be presented as shown in Table 1. The data also show that the non-calcareous clay and silt fractions amount to 20 percent compared to a corresponding lime content of 51 per-cent, which is very high and creates special fertility problems.

The CaCO3 can be found in various size ranges depending on the soil forming factors, which are mainly the parent material and climate. Therefore, knowledge of the particle size distribution of the calcareous and non-calcareous soil materials is of-significance in the study of soil formation and leaching of carbonates.

In a study on soil water diffusivity through the Egyptian calcareous soils by Salim and Massoud (1966), surface samples were collected from the region west of the Delta and analysed for their soil particle and CaCO3, size distribution. The result of the analysis is shown in Table 2.

Table 2. Soil Particle and CaCO3 Equivalent Size Distribution in Calcareous Soils from West of the Delta, Egypt

Soil Texture


Soil Particles-%

Calcium carbonate-%

Total CaCO3

clay

silt

sand

clay

silt

sand

%

Sandy clay loam

20

22

58

27

39

34

26

Sandy clay loam

27

25

48

29

32

39

46

Sandy loam

17

11

72

27

13

60

22

Sandy loam

17

6

77

9

37

54

7

Sand

5

2

93

4

0

96

38

Sand

3

1

96

0

0

100

11


The results show that within the same textural class, the total CaCO3 content may vary considerably and yet it may be the same for different textural classes. As a general trend, the highest percentage of calcium carbonate content is within the silt and clay fraction in the case of sandy clay loam soils and within the sand fraction in the sandy loam and sandy soils. The same trend follows the aridity of the climate since the sandy clay loam soils were taken from Mariut Project and the rest of the samples further to the south.

6.3. Moisture Characteristics

Information on the moisture characteristics of calcareous soils is imperative to the proper planning of their irrigation regime. The moisture tension drying curve is of practical significance in determining the range of soil moisture available for plant growth and its depletion pattern. But to what extent would the presence of CaCO3 affect this range and that pattern in soils of different mechanical composition? To find an answer to this question, a study was carried out on the moisture characteristics of the highly calcareous soils of Mariut extension project, Egypt, Massoud et al. (1971).

As shown in Fig. 1, the shape of the moisture characteristic curves of these highly calcareous soils is similar to that of sandy soils where there is a Barked decrease in the moisture content with increasing tension up to 1.0 atm as compared to that at higher tensions. The same was found by Hassan (1960). This similarity indicates that the moisture may be held to a large extent by weak surface forces. The figure also shows that the soil texture (clay + silt) has a major influence on the moisture retention, whereas CaCO3, (above 20 percent) has only a minor one.

The effect of CaCO3 on moisture retention and/or movement seems to be more related to its effect on the formation of different structural units rather than to the ability of its surface to retain water. Consequently, there will be a better understanding of the effect of CaCO3 on water retention when such studies are carried out on undisturbed samples. However, the statistical analysis of the relation between the moisture retained at 15 atm (PWP) and the silt, clay and clay + silt content in the disturbed samples showed that a high correlation exists between PWP and each of the tested independent variables, especially the clay + silt fraction. In non-calcareous soils we would expect that the moisture retained at 15 atm might be closely correlated with the clay fraction rather than the clay + silt or the silt fractions. But the presence of about 30 percent of the CaCO3 of these soils in the clay fraction, as shown in Table 2, and coating of the clay particle surfaces by CaCO3, as proposed by Hassan (1960), relatively decreases its ability to retain moisture.

Fig. 1. MOISTURE CHARACTERISTIC CURVES OF HIGHLY CALCAREOUS SOILS

The ability of the silt fraction to retain moisture by surface active forces is limited and it may take place physically by forces such as surface tension in the minute interpores. Woodruff (1950) mentioned that the cementing effect of CaCO3 reinforces the capillary walls and this effect increases as the CaCO3 increases with a subsequent reduction of the inner diameter of the capillary pores. Consequently, the water retained in these capillary pores increases against a certain pressure difference. The close correlation found between the clay + silt fraction and the moisture content retained at 15 atm suggests that water retention in these highly calcareous soils is governed by both surface active forces and physical forces.

It has been found that the average available moisture range between 0.33 and 15 atm values for the three dominant textural classes : sandy loam, loam and clay loam is 8.5, 11.9 and 12.6 percent by weight respectively with corresponding 15 atm values (PWP) of 6.3, 8.6 and 11.6 percent. About 50 and 75 percent of the available moisture is depleted at tensions of 1 and 5 atms respectively, regardless of the soil texture. This suggests that the frequency of irrigation in such soils should be closer than in non-calcareous soils.

6.4. Moisture Regime and Plant Growth

The study of plant response to different moisture regimes is significant not only to crop production but also to the water economy and soil conservation. It has just been pointed out that in highly calcareous soils frequent irrigation could be recommended, as deduced from the moisture characteristic curves. In other words, irrigation at a relatively low moisture tension would be advisable. To check on the reliability of this advice, a study was carried out on the effect of moisture regime on the vegetative growth of maize grown on highly calcareous soils, Massoud et al, (1969).

Six sandy loam soils having a different CaCO3 content (23, 35, 40, 45, 55 and 65 percent) and four soils of different texture (loamy sand, sandy loam, loam and silt loam) but about the same CaCO3 content (45 percent) were used in the study. The differential irrigation treatments, which started two weeks after planting and lasted for seven weeks, were given at tensions of 0.33, 0.75, 5 and 10 atm with enough moisture to raise the tension to 0.1 atm.

The effect of moisture regime and CaCO3 content on stalk height, fresh weight and dry weight of plants grown on the sandy loam soils with different CaCO3 content was found to be highly significant. As shown in Fig. 2 the increase in growth followed the sequence of irrigations at tensions of 0.73>0.33>5>10 atm regardless of the CaCO3 content. These tensions correspond to a depletion of 65, 45, 90 and 93 percent of the available moisture between 0.1 and 13 atm values. Irrigating at 43 percent moisture depletion did not give the same good effect as that at 63 percent, probably due to poor aeration. The figure also shows that there is a possibility of doubling the dry weight of plants by following the right irrigation regime. Under a given moisture regime, it is clear that plant growth was adversely affected by increasing the CaCO3 content, especially above 33 percent, probably due to nutritional problems.

Fig. 2 - Effect of CaCO3, content on dry weight of plants irrigated at different soil moisture tensions.

The response to the different moisture regimes by those plants grown on different textured soils and similar CaCO3 content also emphasized the high significant effects of moisture regime on growth. Texture was only significant at the 3 percent level. The response to different moisture regimes followed the sequence mentioned above and better growth was obtained following the increase in clay content.

Although the study was carried out in large pots, the response of the vegetative growth to the different moisture regimes generally agreed with that predicted from the moisture tension curves of highly calcareous soils. Similar studies are recommended for different crops under field conditions with special emphasis on yield rather than the vegetative growth of plants.

6.4. Diffusivity

Mater movement in a soil profile, as a result of certain processes such as surface irrigation, rainfall or sprinkler irrigation, fluctuations of water table and surface evaporation, is governed by basic flow equations whose solutions conform to the boundary conditions. For vertical flow, the equation of continuity can be simply written as

where

q = moisture content on volume basis
t = time
z = vertical distance below soil surface
K = hydraulic conductivity
D = diffusivity
The diffusivity is a soil property which is uniquely defined when the moisture content is specified, Childs and Collis-George (1930), and can be found from the relation.

D = K (dj/dq)

where dj/dq = the inverse of the specific water capacity at a particular value of q.

Prior to the applications of the flow equation to practical problems, the values of K and 0 should be known at different tensions and soil moisture contents. Since D is a soil property that reflects the readiness with which soil conducts water, it is rather important to know how this property behaves in calcareous soils.

The relation between diffusivity of water through soil and calcium carbonate content was studied for calcareous and non-calcareous soils of different texture, Salim and Massoud (1966). The calcareous soils are those given in Table 2. The non-calcareous soils are alluvial sandy loam (clay 10 percent, silt 10 percent, sand 80 percent and CaCO3 1.4 percent) and alluvial sandy clay loam (clay 22 percent, silt 24 percent, sand 54 percent and CaCO3 1.3 percent). The diffusivity was determined following the procedure described by Crank, (1956). The relation between soil moisture content and diffusivity is given in Table 3.

Table 3 - Soil moisture diffusivity "D" of calcareous and non-calcareous soils at different moisture content "q"

The results show that for calcareous as well as non-calcareous soils the diffusivity at a given moisture content is higher in sandy > sandy loam > sandy clay loam soils. Comparing calcareous with non-calcareous soils having about the same particle size distribution we observe that the calcareous soils have higher diffusivity. This means that for the same boundary conditions and under the same moisture gradient the water has a better chance of moving faster through calcareous than non-calcareous soils.

As to the effect of the total carbonate content and its size distribution, it may be said that for highly calcareous soils having about the same soil particle and carbonate size distribution (samples 1 and 2), the total carbonate content above 20 percent has a similar effect on diffusivity. It seems that the presence of CaCO3 in concentrations of about 10 percent has more effect on increasing diffusivity, especially at high moisture content, than when it is above 20 percent. Also the presence of the carbonate in the clay fraction tends to decrease diffusivity (sample 3 as compared with sample 4).

The effect of CaCO3 on diffusivity of calcareous soils could be explained on the same basis given for moisture characteristics. It is known that the presence of calcium carbonate helps the formation of stable aggregates, Chiles (1940), and it seems that the pore size distribution of these aggregates varies according to their CaCO3 content. Within a certain range of CaCO3 content, probably up to 10 or 15 percent, these aggregates have a relatively large proportion of coarse pores and as the CaCO3 content increases, say up to 20 or 25 percent, it will precipitate on the inner walls of the capillary tubes with a subsequent increase of the small pores and a relative decrease in diffusivity. The effect of increasing carbonate beyond this range, as is the case in highly calcareous soils, will depend not on the total concentration but on its size distribution. The coarser the size of the carbonate grains the higher the diffusivity would be.

6.5. Infiltration and Redistribution

Infiltration is the downward entry of water into soils as happens during irrigation or rainfall. After the cessation of the irrigation or the removal of surface water, the water continues to move downwards for some time under the influence of water content gradient and the gravitational field with a subsequent alteration in the moisture profile. This process is known as the redistribution of infiltrated water. When the water table is at too great a depth below the soil surface to influence water movement near the surface, the rate of downward movement and redistribution of water also slows down with time until it appears to have ceased. This means that the redistribution of moisture in soil is a slow, continuous process which usually involves further penetration of the water front at the expense of the upper regions. The water content, which exists when this downward movement becomes negligible, is usually known as the field capacity. Thus the moisture content at field capacity is not a state of static equilibrium but should usually be considered in terms of dynamic equilibrium.

The practical aspects of infiltration and redistribution of moisture in soils are of significant importance to irrigation practices and soil and water conservation. If the infiltration rate is less than the rate of water application to the soil surface, ponding or runoff will occur depending on the slope of the surface and its configuration. Time and soil properties such as diffusivity, hydraulic conductivity and initial moisture content affect these processes. So, the presence of a surface crust, or a relatively impervious layer within the profile, controls these processes. In calcareous soils where the formation of crust and hardpan is to be expected, the infiltration rate would be less than in a normal uniform soil, Hillel and Gardner (1970). It is through soil management practices, such as proper tillage and addition of organic matter, that the infiltration rate can be improved. For efficient irrigation one has to account for water re-distribution in the soil profile. Depending on the effective rooting depth of the irrigated crops, the amount of irrigation water should replenish the soil reservoir after its redistribution to that depth. Under rainfed farming the amount of rainfall stored in the soil profile and its redistribution pattern are among the main factors that determine the rooting characteristics and the yield of the crop.

The moisture profile during infiltration can be computed from the solution, given by Philip (1957), of the continuity equation mentioned before, when the diffusivity and conductivity are known. In a study by Soliman (1968) on infiltration and redistribution of water in a highly calcareous sandy soil (clay 3 percent, silt 10 percent, sand 87 percent and CaCO3 33 percent) the agreement between the experimental and calculated moisture profiles was found to be good as shown in Fig. 3. In other words the solution given by Philip adequately predicted the shape of the wetting front and depth of penetration.

Fig. 3 Measured and calculated soil moisture profiles of air dry calcareous soil for vertical movement.

Fig. 4 Moisture profiles during the redistribution after infiltration to (a) 25 cm and (b) 50 cm depth (numbers near profiles refer to the time in minutes after the cessation of infiltration)

For the same soil, the development of the moisture profile during redistribution after infiltration of 8.2 and 16.7 cm of water to corresponding depths of 25 and 50 cm is given in Fig. 4. It is clear that redistribution has proceeded at a fast rate after cessation of infiltration due to existence of moisture gradient and high "D" and "K" values. But as time elapses and the moisture content decreases, with a consequent sharp decrease of “D” and "K", the rate becomes much slower. Although the figure indicates that a true equilibrium cannot be achieved and some movement is always found, one could consider the moisture content of the moisture profile attained at the end of about 1.5 days after the cessation of infiltration as the so-called field capacity.

Under practical field conditions, the development of such ideal moisture profiles would be affected by the soil structure, stratification, surface evaporation, root extraction and ground water contribution. Therefore, it is advisable to run field tests for infiltration and development of moisture profiles during redistribution in order to have a true picture of the water storage capacity of the soil.

6.6. Soil Crusting and the Moisture Regime

Soil crusting can be considered as one of the main problems of the newly reclaimed calcareous soils. Crusts do not only affect infiltration and soil aeration but also the emergence of seedlings. Games (1934) reported that the amount of crust formed on a soil depends on the amount of rain and that the slower the drying rate the harder the crust whose strength bears an inverse relationship to its moisture content at time of breaking. Isiumov (1940) indicated that crust formation is influenced by a heavy mechanical composition of soil combined with temporary excessive moisture. Lemos and Lutz (1957) have demonstrated the influence of many factors on crust strength. Increasing silt or the fraction less than 0.1 mm, 2:1 type clay mineral, compaction by rainfall and soil puddling, increase crust strength while successive cycles of wetting and drying decrease it.

In a study on the effect of moisture regime on crust formation in highly calcareous soils, Massoud et al. (1968), it was observed that in a silt loam soil (clay 7 percent, silt 65 percent, sand 28 percent and CaCO3 43 percent) soil crusting was more obvious than in a loam or a clay soil. To the silt loam soil packed in pots, six water levels (0.3 F.C. - 5 F.C.) were applied to the surface except for the lowest treatment where water was sprinkled from a 1.5 metre height. The time at which cracking started to develop and crusts were formed and could be easily separated from the sub-crusts was recorded. Twenty-five days after the water application, samples were taken from the crust and sub-crust for the determination of moisture content, bulk density, salinity, CaCO3 content and mechanical analysis. This procedure and analysis was repeated for four wetting and drying cycles. The significant results are given in Table 4.

The results indicate that heavy water applications delayed cracking and crusting while very light applications and successive wetting and drying enhanced their formation. It has been observed that the thickness of the crust increased five-fold by increasing the water application from 0.3 to 5 F.C. The most significant difference between the crust and sub-crust was the increase in the bulk density of the crust relative to the soil beneath it, which is in agreement with the results obtained by Hillel (1960). The ECe was also higher in the crust but the differences became less as the water application successively increased.

The mechanism of crust formation in calcareous soils seems to follow a sequence of processes involving slacking and breakdown of aggregates, segregation, solution of Ca(HCO3)2, rearrangement of particles and redeposition and cementing by CaCO3 on desiccation. In the light of this sequence the highly calcareous silt loam soil, which might be expected to form a consolidated aggregate when dry, becomes soft and friable when wet and breaks easily in the presence of water and by the impact of sprinkled water drops. Following this destruction of the aggregates and the dispersion of the particles some segregation between different sizes would occur, especially in the surface soil and, consequently, a closer packing of the soil particles which increases the bulk density of the crust. The formation of a relatively massive crust in soils receiving heavy water applications is related to the fact that the rate of drying is slower than in those receiving lighter applications and the drying of the latter is helped by the presence of cracks.

Table 4 - Effect of moisture regime on time of cracking and crusting and bulk density (gm/cm3) of a highly calcareous silt loam soil

Water Application



First Cycle

Fourth Cycle

Cracking

Crusting

Bulk density

Cracking

Crusting

Bulk density

days

days

crust

sub crust

days

days

crust

sub crust

0.3 F.C.

1

1

1.60

1.30

1

3

1.60

1.30

0.3 F.C.

1

14

1.60

1.20

1

11

1.78

1.36

2 F.C.

1

16

1.66

1.20

1

13

1.78

1.39

3 F.C.

-

19

1.69

1.27

2

14

1.80

1.40

4 F.C.

-

20

1.69

1.30

2

15

1.82

1.41

5 F.C.

-

24

1.71

1.32

2

17

1.85

1.45


From the practical point of view where soil crusting occurs, the frequency of irrigation should be close enough to prevent drying of the soil surface and hardening of the crust, especially under heavy water application.

6.7. Soil Crusting and Seedling Emergence

Extensive work has been done on the nature and properties of soil crust and its relation to the emergence of various seeds. Hanks (1960) cited references indicating that seedling emergence may be limited by insufficient oxygen diffusion at the seed depth, limited moisture or high mechanical strength of surface crust. He showed that seedling emergence will be limited when the soil dries because of the increase in crust strength and the decrease in the ability of the seedling to emerge at a given crust strength. Parker and Taylor (1965) found that the soil moisture tension, planting depth and plant species affected grain sorghum emergence at specified soil strength. Taylor et al. (1966) studied the relation between soil strength as measured with a penetrometer and the emergence of corn, onions, barley, wheat, switch grass and rye seedlings. They found that the percentage of the tested graimeae which emerged slightly decreased as crust strength increased to the range of 6 to 9 bars and no emergence occurred above the range of 12 to 18 bars while emergence of onion was prohibited at 2 bars.

The effect of soil crusting on wheat seedling emergence was studied in highly calcareous soils by Massoud et al, (1968) where factors such as moisture tension, texture, carbonate content and thickness of the crust were investigated. Four soils (Group I) with about 45 percent CaCO3 and different texture (loamy sand, sandy loam, loam and silt loam) and another four sandy loam soils (Group II) with varying CaCO3 content (25, 35, 40 and 45) were packed to a bulk density of 1.3 gm cm3 in short brass cylinders 2, 2.5, 3 and 4 cm high and 7 cm in diameter. The moisture content of the saturated soil columns was brought to equilibrium at tensions of 0.1, 0.33, 0.4, 0,5 and 0.6 atm. Germinated wheat seeds placed on top of the 2.5 cm columns were covered with the 2,3 and 4 cm columns, gently pressed to ensure good contact and thus behave like soil crusts of known moisture tension at the time of seedling emergence. Seedling emergence was recorded daily for 10 days as well as the length of each seedling. The moisture content of the top columns (crusts) and lower columns (sub-crusts) was determined at the end of the experiment.

The results showed that the moisture tension of the crust at the time of emergence has a highly significant effect on the initial and ultimate time of emergence, Fig. 5, as well as the ultimate number of emerging seedlings, Fig. 6. Increasing soil moisture tension of the crust delayed emergence and decreased it especially between 0.33 and 0.4 atm. The length of the seedlings was highly affected by the soil moisture tension. The average weighted means of seedling length on the 10th day were 18, 16, 6. 8 and 6 cm where the initial moisture tensions of the crust were 0.1, 0.33, 0.4, 0.5 and 0.6 atm respectively.

Fig. 5 - Relation between initial moisture tension of crust and time of emergence.

Fig. 6 - Effect of initial moisture tension of crust on ultimate emergence.

Apart from the effect of soil moisture tension on seedling emergence and growth, it also affected the crust strength. From the known initial and final moisture contents of the crust, it was possible to estimate its average rate of drying which became slower as its moisture tension increased above 0,33 atm and consequently the crust became harder.

The thickness of the crust was found to affect the rate of emergence as well as its ultimate percentage. Doubling the thickness of the crust delayed emergence by two day but reduced it by about 35 to 50 percent.

The effect of the crust texture was significant only on the ultimate percentage of emerging seedlings which was highly correlated with the clay content (r = -0,99) followed by silt + clay (r = -0.74) and finally with silt (r = -0.63). Further statistical analysis showed that the moisture content at a given tension was positively correlated with clay and silt + clay which should help increasing emergence. Since this was not the case, it could be suggested that increasing the clay content led to an increase in the crust strength as found by Banks (1960).

The effect of the CaCO3 content of the crust was slight on rate of emergence but significant on the percentage of ultimate emergence. Moreover, the average ultimate percentage of emergence with respect to CaCO3 content was relatively low, being 41, 51, 45 and 47 for crusts having CaCO3 of 25, 35, 40 and 50 percent respectively. It seems that the effect of CaCO3 on crust strength and wheat seedling emergence became detrimental at a level below 25 percent especially if coupled with high moisture tension and deep seeding.

From the practical point of view, the study recommended that in order to have a good wheat stand in highly calcareous soils, the moisture tension of the crust during emergence should be kept low (below about 0.33 atm) and that planting depth be relatively shallow (less than 4 cm). Since in heavier textured soils the crust tends to be harder, the amount of seeds needed for planting may also be increased.

It could also be possible through some other planting techniques to overcome the hazardous effects of soil crusting on seedling emergence. Such techniques should be tried for various crops. In a study on maize seedling emergence in highly calcareous sandy loam soil (CaCO3 28 percent) by Massoud et al. (1969) the effects of moisture content at the time of planting, planting method (furrow versus surface), planting site, irrigation (heavy versus light) and number of seeds per hill were investigated under field conditions.

The effect of moisture content was studied under furrow and surface planting. Different moisture levels at the time of planting were achieved by planting just before irrigation, 1, 2, 3, 4 and 5 days after in the case of furrow planting, and before irrigation, 2, 4, 6, 8 and 10 days after in the case of surface planting. The results given in Table 5 indicate the significant effects of the moisture content on maize seedling emergence and that the highest emergence was achieved when seeds were irrigated right after sowing regardless of the planting method.

Table 5 - Ultimate maize seedling emergence as affected by soil moisture content and planting technique


Treatment1/

Furrow planting

Surface planting

Days after irrigation

Pw at time of planting %

Ultimate emergence after 10 days - %

Days after irrigation

Pw at time of planting %

Ultimate emergence after 10 days - %

A

0

22.5

92.3

0

23.5

95.0

B

1

16.1

36.4

2

14.7

33.0

C

2

12.5

41.7

4

11.7

49.2

D

3

11.3

67.3

6

9.4

59.2

E

4

8.4

65.2

8

8.2

54.8

P

5

7.9

54.2

10

6.2

39.7

1/ In treatments B and C seeds were covered by puddled soil; in D, E and F seeds were covered by broken crust.
Planting the seeds in a wet soil means they will be covered by a puddled soil which reduces emergence as a result of forming a hard crust upon drying, as found by Lemos and Lutz (1957). Breaking the crust improved emergence. Generally, the moisture content, soil puddling and breaking of the crust had more pronounced effects on emergence of maize seedlings than the planting method.

Under furrow planting, the site of sowing was found to have a significant effect on emergence whether light or heavy irrigations were applied right after sowing. The ultimate emergence ten days after planting seeds on top, in the upper third and lower third of the ridge was 54, 80 and 94 percent with heavy irrigation and 44, 69 and 91 percent with light irrigation respectively. Since the moisture content at the planting sites was initially about the same, the reduction in emergence could probably be attributed to the higher soil dryness and the increased crust strength of the top and upper third of the ridge in relation to the lower third, especially in the case of light irrigation.

Regarding the effect of number of seeds per hill on emergence, the result showed that planting of 1, 2, 3, 4 and 5 seeds per hill gave ultimate emergence of 70, 89, 90, 92 and 95 percent respectively. The rather insignificant effect due to increasing the number of seeds from 2 to 3 is due to the fact that maize seedlings, like wheat, worm their way through the crust and do not push on it as is the case with cotton seeds and other dicotyledons.

6.8. Crust Strength

Strength is one of the important properties of soil, not only in relation to plant production but also to construction works. Various methods have been used to measure soil strength and to find out how it is affected by other soil properties. Proctor (1933) developed the soil plasticity needle and found that a curve relating the resistance to penetration with the moisture content could be developed. Henin (1936) used a penetrometer to obtain an index of tilth. Richards (1941) described an expensive penetrometer and showed that seedlings were affected by the presence of plant roots, soil moisture and a compacted layer in the soils Show et al. (1942) found a very rapid increase in resistance (as measured by a penetrometer) with decreasing moisture. The modulus of rupture has been used as an index of crusting by Richards (1953), Allison (1956), Lemos and Lutz (1957) and Hanks (1960). Taylor and Gardner (1963) used waxes as a substratum in root penetration studies measured by ASTM penetrometer. Taylor et al. (1966) used a force gauge as a static penetrometer to determine the strengths of the upper surface and concluded that soil strength and not the bulk density should be considered as the critical impedance factor controlling root penetration.

Factors affecting crust strength of highly calcareous soils were studied by Massoud et al. (1968). The effects of moisture tension, bulk density particle size and CaCO3 content were investigated on twenty-seven samples varying in texture from sand to clay and in CaCO3 content from 18 to 68 percent. Soil packed to specified bulk densities in short columns 4 cm high and 7.5 cm in diameter and equilibrated to the desired moisture tension were considered as simulating crusts of known bulk densities and moisture tensions. Using the ASTM-D 5 Penetrometer, the penetration distance expressed in 0.1 mm and referred to as the penetration number (P.N.) was taken as an index to crust strength; the higher the P.N. the lower the strength.

The effect of moisture tension at 0.15, 0.25, 0.35, 0.5, 0.75 and 1.0 atm on penetrability was studied in sandy clay loam (bulk density 1.30 gm/cm3) and sandy soils (bulk density 1.55 gm/cm3). The results are shown in Fig. 7. Increasing the moisture tension reduced penetrability, especially below 0.5 atm. Recalling the moisture characteristics of these highly calcareous soils, where most of the water is depleted at low tension, closer arrangements of the soil particles and more coherence between them will take place and, consequently the crust strength will increase. Higher penetrability of the sandy soil is probably due to the larger percentage of coarse pores and to its lower ability to shrink and rearrange in closer packing upon drying.

FIG. 7 EFFECT OF SOIL MOISTURE TENSION ON PENETRATION NUMBER

The effect of bulk density was investigated using sandy clay loam and sandy soils at three moisture tension levels. The results are given in Fig. 8. at a given soil moisture, penetrability decreased when there was an increase in the bulk density due to closer packing. For soils having the same moisture tension and bulk density (1.7 gm/cm3). it was found that the lighter the soil the higher the penetrability, which reflects the importance of particle and pore size distribution.

FIG. 8 PENETRATION NUMBER AS RELATED TO SOIL BULK DENSITY AT THREE MOISTURE TENSION LEVELS.

To investigate the role of high CaCO3 content in crust strength, penetrability was measured in all the samples at tensions of 0.25, 0.50 and 1.0 atm and a hulk density of 1.3 gm/cm3. The following linear relationships between CaCO3 content and P.N. were obtained.

P.N.

=

151 - 0.92

CaCO3 at 0.25 atm

P.N.

=

69 - 0.16

CaCO3 at 0.50 atm

P.N.

=

45 - 0.006

CaCO3 at 1.0 atm


The effect of increasing CaCO3 above 18 percent on reducing penetrability became less obvious as the crust became drier and was almost nil at a tension of 1.0 atm. In other words, the cohesive forces between soil particles at relatively high tensions became so strong that the effect of increasing CaCO3 became less obvious.

The relation between clay, silt and sand content of the soil crust and its strength was obtained from the previous measurements. The results generally show that the penetrability decreased with increasing clay and silt contents but the sand had a positive correlation. Fig. 9 gives the relation between the silt content (50 - 20 microns) and the penetration number.

FIG. 9 EFFECT OF SILT CONTENT ON PENETRATION NUMBER AT THREE SOIL MOISTURE TENSION LEVELS

The silt had a more pronounced effect on crust strength than the clay especially at low tensions. In the case of clay sliding the penetrometer needle through the crust might be easier as the moisture content increases by having more clay, but the increase in mechanical impedence tends to oppose the moisture effect. In the case of silt, the mechanical impedance was more effective than that of the moisture content.

To evaluate the relative importance of each of the studied factors on penetrability, statistical analysis was applied to the data obtained at a tension of 0.5 atm. The estimated coefficients and the corresponding t-values are given in Table 6.

Table 6 - Estimated coefficients and corresponding t-values

Item

Coefficient

Calculated t-value for the exponent 1/

Bulk density

- 1.539

74.8

Soil moisture tension

- 0.853

14.4

Silt

- 0.317

27.2

Silt + Clay

- 0.309

27.4

Sand

+ 0.287

26.8

Clay

- 0.219

31.9

CaCO3

- 0.155

10.9

1/ Significant at the probability level 0.01.
It is clear that all the estimated coefficients are statistically highly significant. Since the exponent coefficients represent the elasticities of the estimated functions, they can be used to evaluate the relative importance of each of the studied factors. It is clear that all the factors, except sand, inversely affect penetrability of the highly calcareous soils. Their relative importance follow the sequence bulk density> moisture tension > silt > silt + clay > sand > clay > CaCO3.

6.9. Soil Tilth

Tilth is commonly defined as the physical condition of the soil in its relation to plant growth. Adequate aeration, ready infiltration of irrigation water and rainfall and sufficient moisture storage are important functions of good tilth. All tillage operations should aim at the creation and maintenance of good tilth. However, different tilth may be obtained depending on the tillage operations and the physical conditions of the soil at the time of tillage. In highly calcareous soils where crusting and formation of hardpans can be expected special consideration should be given to tillage. The selection of the right plough type, tillage sequence, ploughing depth and moisture content at the time of ploughing should provide good soil tilth.

In a study by Massoud et al. (1968), the effect of different tillage implements and techniques on tilth of highly calcareous soils was investigated. Three sets of experiments were carried out in an area of about 33 acres of a sandy loam soil with 35 percent CaCO3. The lowest value of the soil bulk density and the highest average infiltration rate (for a period of one hour) were taken as indices to good tilth. In the first experiment, the effect of the tillage implements and the sequence of tillage operations was studied at an average moisture content of 7.8 percent within an average ploughing depth of 20 cm. The bulk density was determined for a volume of 1 × 1 × 0.2 m3, while for the infiltration rate the measurements were taken from a basin 1 × 1 m2. The results are given in Table 7 in descending sequence of their preference.

In the second experiment, the effect of ploughing depth at an average moisture content of 7 percent was studied using a mouldboard followed by a chisel plough in a perpendicular direction. The results are given in Table 8 in descending sequence of their preference.

The effect of soil moisture on tilth was studied using a mouldboard followed by a chisel plough and a ploughing depth of 25 cm. The results are given in Table 8.

From the results of the study, it is obvious that the infiltration rate, as an index to moil tilth, is more sensitive to tillage operations and techniques than the bulk density. The infiltration rate may vary up to fourfold by a change in the tillage implement and sequence. The selection of the right depth of ploughing and moisture content at the time of ploughing could raise the infiltration rate by 60 to 70 percent.

The study recommended the use of the mouldboard followed by the chisel plough in a perpendicular path with a ploughing depth of 25 cm at an optimum moisture content of about 7-8 percent.

Table 7 - Effect of tillage implements and sequence of tillage operation on bulk density and infiltration rate

Tillage implements and sequence of operations

Average bulk density

Average infiltration rate.

First path


Second path in perpendicular

gm/cm3


cm/hr


direction to the first

Mouldboard

Chisel

0.97

15.4

Mouldboard

Heavy duty disc harrow

1.08

11.4

Lister

Chisel

1.12

10.5

Chisel

Chisel

1.15

9.9

Lister

Heavy duty disc harrow

1.18

9.3

Mouldboard & disk spike


1.34

3.7

Boiler & Sowing harrow




Unplowed soil

1.50

3.4


Table 8 - Effect of tillage depth and moisture content on bulk density and infiltration rate

Plowing depth

Bulk density

Infiltration rate

Moisture content

Bulk density

Infiltration rate

cm

gm/cm3

cm/hr

%

gm/cm3

cm/hr

25

0.97

15.4

7.8

0.94

16.9

30

1.03

12.6

6.9

1.03

12.6

20

1.07

11.4

9.0

1.07

11.6

33

1.10

10.7

9.2

1.10

10.6

15

1.17

9.7

6.0

1.16

9.9


REFERENCES

Allison, L.E. 1956, Soil and plant responses to VAMA and HPAN soil conditioners in the presence of high exchangeable sodium. Soil Sci., 20, 147-151.

Carnes, A. 1934, Soil crusts, method of studying their strength and a method of overcoming injury to cotton stands. Agr. Eng., 15, 167-171

Childs, E.G. 1940, The use of soil moisture characteristics in soil studies, Soil Sci., 50 239-252.

Childs, E.C. and Collis-George, N. 1950, The permeability of porous materials. Proc. Roy. Soc., 201 A, 392-405.

Crank, J. 1956, The Mathematics of Diffusion, Oxford University Press

Day, P.R. 1956, Particle fraction and particle-size analysis. In C.A. Black (Ed.), Methods of Soil Analysis (Part 1), Am. Soc. Agron., Madison, Wisconsin.

Drouineau, G. 1942, Dosage rapide du calcaire actif de sol. Ann. Agron., 12, 441-450.

Hanks, R.J. 1960, Soil crusting and seedling emergence. Trans. Int. Soil Sci. Cong., 7th, I, 340-346.

Hassan, F.A. 1960, Effect of calcium carbonate upon water retention by soils. M.Sc. (Thesis), Alexandria University, Faculty of Agriculture Library, Alexandria, Egypt.

Henin, S. 1936, Quelques résultats obtenus dans l'étude des sols & l'aide de la sonde dynamométrique de Demolon-Hénin. Soil Res., 5, I.

Hillel, D. 1960, Crust formation in loessial soils. Trans. Int. Soil Sci. Cong., 7th, I, 330-339.

Hillel, D. and Gardner, W.R. 1970, Transient infiltration into crust-topped profiles. Soil Sci. 109, 69-76.

Isiumov, A.N. Control of soil crust (packing). Pedology 10, 1313-1321, Abstract in 1938 soils and Fertilizers 3, 66, 1940.

Kadry, L.T. 1972, Distribution of calcareous soils in the Near East Region, their reclamation and land use measures and achievements. FAO/UNDP Regional Seminar on Reclamation and Management of Calcareous Soils, (in press).

Lemos, Petezval and Lutz, J.F. 1957, Soil crusting and some factors affecting it. Soil Sci. Soc. Amer. Proc., 21, 485-491.

Massoud, P.I. Elgabaly, M.M. and Eltalty. 1971, Moisture characteristics of the highly calcareous soils of Mariut extension project, Egypt. Alexandria J. Agr. Res., 19, 351-357.

Massoud, P.I., Elgabaly, M.M. and Elyassaki, A.M. 1969, Maize seedling emergence in highly calcareous soils as affected by soil moisture, planting site and number of seeds per hill. Proc. UAR Soil Sci. Soc. Cong. 4th, Cairo, UAR.

Massoud, F.I., Elgabaly, M.M. and Esmail, E.K. 1968, Effect of soil crust on wheat seedling emergence in highly calcareous soils. Proc. UAR Soil Sci. Soc. Symp. on Calc. Soils, Alexandria, UAR.

Massoud, F.I. Elgabaly, M.M. and Girgis, F.F. 1968, Study of some factors affecting penetrability of highly calcareous crusts. Proc. UAR Soil Sci. Soc. Symp. on Calc. Soils. Alexandria, UAR.

Massoud, F.I., Elgabaly, M.M., Hassan, M.N. and Abou Amin, F. 1968, Effect of different water applications on crust formation in highly calcareous soils. Proc. UAR, Soil Sci. Soc. Symp, on Calc. Soils, Alexandria, UAR.

Massoud, F.I., Elgabaly, M.M. and Zaki, L.F. 1969, Effect of moisture regime on the vegetative growth of corn in highly calcareous soils. Proc. UAR Soil Sci. Soc. Symp. on Calc. Soils, Alexandria, UAR.

Massoud, F.I., Elhossary, A.M., Elgabaly M.M. and Mabrouk, M.A. 1968, Effect of different tillage implements and techniques on tilth of a highly calcareous sandy loam soil. Proc. UAR Soil Sci. Soc. Synp. on Calc. Soils, Alexandria, UAR.

Menon, R.C. 1971, Report of the work done in the soils laboratory, UNSF Ghab development project, Syria.

Parker, J.J. and Taylor, H.M. 1965, Soil strength and seedling emergence relation, I. Soil type, moisture tension, temperature and planting depth effects. Agron. J., 57, 288-291.

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Richards, S.J. 1941, A soil penetrometer. Soil Sci. Soc. Amer. Proc., 6, 104-107.

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7. Soil and Water Management Practices for Calcareous Soils1/

by

R.D. Jackson
Research Physicist

and

L.J. Erie
Research Physicist and Agricultural Engineer
U.S. Water Conservation Laboratory, Phoenix, Arizona

1/ Contribution from the Soil, Water, and Air Sciences, Western Region, Agricultural Research Service, U.S. Department of Agriculture.
SUMMARY

Soil and water management practices for calcareous soils encompass a wide range of interests, from the microscopic flow of water in fine pores to the overall hydrologic and water quality assessment of entire river basins. This paper reviews some recent research on the application of soil-water flow theory to field situations, trends in irrigation practices and scheduling in the southwestern United States, and advances in river basin salinity control.

The application of soil-water flow theory to field situations requires assumptions and simplifications in the exact theory to allow for the non-homogeneities of a field soil. Approximate solutions have been developed to predict soil profile infiltration and drainage. Leaching of salts from the root zone requires less water for the same amount of salt removed if the soil is maintained unsaturated.

Some soils require minimum tillage to maintain infiltration rates high enough for adequate leaching of salts. Some tillage practices are designed to minimize accumulation of salts and to provide adequate moisture to germinating seeds. A trend in irrigation practices is toward "dead level" basins, ranging from 2 to 16 hectares. Dead level basins are very efficient from the point of view of water application efficiency and salt control. Consumptive use data for specific crops and computer forecasting are now used for irrigation scheduling.

7.1. Introduction

Soils that have weathered under arid climatic conditions are characterized by an accumulation of calcium carbonate at some point in the profile. This accumulation may be rather concentrated in a narrow zone or more dispersed, depending upon the quantity and frequency of rainfall, topography, soil texture and vegetation. In some soils the calcium carbonate deposits are concentrated into layers that may be very hard and impermeable to water. These caliche layers are formed by rainfall (at nearly constant annual rates) leaching the salts to a particular depth in the soil at which the water content is so low that the carbonates precipitate. They are also formed by salts moving upward from a water table (caused by irrigation) and precipitating near the top of the capillary fringe. Caliche layers are only one of many factors to be considered in a soil and water management programme for calcareous soils.

A major characteristic of calcareous soils is that they develop in regions of low rainfall and must be irrigated to be productive. Frequently, the irrigation water is the cause of many management problems. Almost all waters used for irrigation contain inorganic salts in solution. These salts may accumulate within the soil profile to such concentrations that they modify the soil structure, decrease the soil permeability to water, and seriously injure growing plants.

In managing calcareous soils, too major objectives are to provide optimum water for plant growth without waste and to control salts. The two objectives are essentially contradictory, in that a water management practice that provides optimum water with no wastage may allow salts to accumulate and a practice to control salts requires water in excess of that required for optimum plant growth. Obviously, practical experience and a knowledge of basic principles are required for a successful soil and water management programme.

Often managers must look beyond an individual farm and be concerned with an irrigation district and even an entire river basin. Irrigation waters diverted at downstream locations contain salts leached from soils upstream and returned to the river through drainage channels and by underground flow. Agricultural communities are becoming more concerned with the return flow of irrigation waters to rivers and groundwater basins. In addition to the natural soluble salts in the drainage water, fertilizers and pesticides applied to the soil appear in the return flow and may present a hazard to downstream municipal users of the water. Thus, a comprehensive soil and water management programme must encompass a wide range of interests, from the microscopic flow of water in very fine pores to the overall hydrologic and salinity assessment of entire river basins.

This paper presents a brief review of some basic principles and some practical methods of soil and water management for calcareous soils in the southwestern United States. Much of the information is readily applicable to other regions in which calcareous soils are irrigated.

7.2. Basic Principles

Managing calcareous soils for optimum crop production requires a mixture of practical experience and scientific knowledge Some areas have been in production for centuries with the farmer or manager relying solely on practical knowledge passed to him by ancestors and obtained from his own experience. Soil and water science is relatively new, beginning a little over a century ago, with the main impetus occurring during the past three decades. A tremendous amount of information has been obtained concerning soil physical and chemical properties, water movement through soil, water quality, salt reactions in water and soil, water management and irrigation requirements, not all of this basic information has been applied to improve management practices. Two possible reasons for this lack of application are: (a) insufficient information for bridging the gap from experiment to application, and (b) the natural reluctance of some managers to incorporate untested ideas in their management programme. In the following sections we will review some basic principles and, where possible, indicate the status of current research and point out areas where future research may be needed.

7.2.1. Water movement

Soil and water management practices are influenced by the rate at which soil will conduct water. Irrigation scheduling, salinity control practices and drainage design are examples of practices that are determined by the rate of movement of soil water. Soil water flow theory is based upon the equation (in one dimension)

dq/dt = d(KdH/dz)/ dz

(1)


where q is the volumetric water content, t the time, K the hydraulic conductivity, H the hydraulic head, and z the vertical distance below the soil surface. An alternate form of equation (1) is

dq/dt = d(Ddq/dz)/ dz + dK/dz

(2)


where D = Kdh/dq is the soil water diffusivity, and h is the soil-water pressure head. The transfer parameters K and D always appear in solutions to equations (1) and (2). Methods for measuring K and D have been reviewed by Klute (1972) and by Bouwer and Jackson (1972).

Both K and D are strongly dependent on water content and pressure head. Thus solutions of equations (1) or (2) are difficult to obtain. Computers are frequently used to obtain numerical solutions to the equations. Another complication is that the relation between q and h is assumed to be unique, whereas it is hysteretic.

The heterogeneity of field soils limits the applicability of equations (1) and (2). The coefficients K and D may vary widely both horizontally and vertically within a field. Nevertheless, some approximate solutions of the equations have been successfully applied to field situations (Nielsen et al. 1972). For example, Black et al. (1969) integrated equation (1) from the soil surface to depth L. By assuming that a unit hydraulic gradient prevails and that no evaporation occurs at the surface during drainage, they obtained


(3)


where is the average water content in the profile from 0 to L. Davidson et al. (1969) measured K in the field at several depth intervals and, for a silty clay soil, approximated the conductivity-water content relation with the expression


(4)


where a is a constant and the subscript s refers to the saturated condition.

Substituting equation (4) into (3) and integrating yields the average water content for the profile as a function of time. Differentiating that result with respect to t yields


(5)


which gives the flux q at the depth L as a function of time. Fig. 1 shows the measured and calculated flux at the 152 cm depth for Miller silty clay as a function of time, The agreement between measured and calculated is quite good, when the simplifying mathematical assumptions and the variability of field soils are considered.

Information predicted by equation (5) and shown in Fig. 1 is useful for predicting the amount of water that would move out of the root zone. Such information aids in estimating the quantity of irrigation water required for leaching or for maximum efficiency of irrigation.

Figure 1 Measured and theoretical soil water flux at 152 cm in Miller silty clay following a heavy irrigation (Davidson et al. 1969).

Philip (1957) solved equation (2) for the infiltration of water into soils. The solution was in the form of an infinite series in which, for short times, only the first two terms are important. The resulting expression is


(6)


where I is the accumulative infiltration in time t. The sorptivity (S) is essentially a measure of the capacity of the medium to absorb or desorb liquid by capillarity. The term A is approximately equal to two-thirds of the saturated conductivity (Ks).

The infiltration rate (i) is obtained from (d) by differentiation, that is,


(7)


Equation (7) indicates that the infiltration rate will be high for a short time, then decrease rapidly with time and approach a constant. This behaviour is well known from field experience. When the infiltration rate approaches a constant, it is known as the "final" infiltration rate.

In addition to theoretical equations, a host of empirical equations have been proposed to predict infiltration rates. Whisler and Bouwer (1970) compared several equations, including equation (7). They stated that equation (7) gave useful results if S and A were evaluated statistically from measurements of infiltration. Watson (1959) found that equation (7) represented field infiltration rates particularly well for short times.

Field evaluation of infiltration rates in calcareous soils may be complicated by caliche layers or by hardpans formed by tillage. If the measurement is made over a small area, the slowly permeable layers may cause the infiltrating water to move horizontally as well as vertically, resulting in an abnormally high value for the infiltration rate. Evans et al. (1951) have discussed this situation in detail, and Erie (1962) has discussed the evaluation of infiltration measurements.

The studies of Van Bavel et al. (1968) and Rose and Stem (1965) have shown how soil water flow theory can be used to describe the dynamic nature of soil water in cropped soils. Although advances have been made in applying soil-water flow theory to field situations, the accuracy of the results when applied to large land areas remains to be evaluated. Furthermore, the present theories of infiltration and water movement within the profile do not account for the observed fact that infiltration rates and sometimes water flow rates in the profile, decrease as the growing season progresses. This may be the result of tillage operations, the interaction of salt with the soil particles to cause dispersion of aggregates, or other factors. More research is needed in this area to further develop the best soil and water management practices for optimum crop growth and water savings.

7.2.2. Salt and water movement

Salts move within the soil profile by being carried along with moving liquid water and by diffusion. From fundamental studies of salt and water movement during the past ten years a clearer concept of the leaching of salts from the soil profile has evolved, leading to recommendations of new leaching practices.

The size of pores and channels through which water flows in soil varies from millimicrons to millimetres. The rate of water flow through these channels is approximately proportional to the square of the radius of the channel. Thus, large channels conduct water much faster than the smaller ones, and most of the water moves through the large channels. Salt accumulations in the soil are distributed throughout the range of channel sizes. If water is ponded on the soil surface, the soil becomes saturated and most of the flow takes place through the large channels, Salts in these channels are flushed out, but salts remain in the smaller pores. After the ponded water infiltrates and the soil becomes unsaturated, the large channels drain, and the flow of water and salt continues through the smaller pores. If the soil is unsaturated, less water is required to remove an equal quantity of salt than if the soil is saturated.

This phenomenon is exemplified by Fig. 2 taken from a study by Nielsen et al. (1964).

Figure 2. Distribution of chloride concentrations in the soil solution of Panoche clay loam when the soil surface was continuously ponded. Numbers on each curve represent the centimetres of water that had infiltrated at the time of measurement (Nielsen et al. 1964)

Figure 2. Distribution of chloride concentrations in the soil solution of Panoche clay loam when the soil surface was intermittently ponded with irrigation water. Numbers on each curve represent the centimetres of water that had infiltrated at the time of measurement (Nielsen et al. 1964)

The chloride concentration as a function of soil depth is shown for a continuously ponded (Fig. 2 (a)) and an intermittently ponded treatment (Fig. 2 (b)). Comparison of curves in the two figures for the same amount of water infiltrated shows that the intermittent ponding treatment moved more salt to lower depths in the profile. The concentration of salt at all soil depths down to 137 cm was less with 66 cm of intermittently ponded irrigation water than with 102 cm of continuously ponded water. The continuously ponded treatment caused the salt to be spread through a greater depth of soil before being leached out of the profile.

Oster et al. (in press) compared the salt-removing efficiencies of continuous ponding, intermittent ponding and sprinkler irrigation. They found that for all treatments salt reduction was most rapid immediately after the first application of water. Their study confirmed results from earlier studies and demonstrated that leaching by intermittent ponding or sprinkling used less water than continuous ponding and achieved the same degree of leaching in the same period of time on their soil.

The fact that salt is readily leached from soil even when the soil-water content is relatively low raises the question of how dry the soil must be before salt does not move. In a bare soil, salt accumulates near the surface as a result of water moving to the surface and evaporating. Nakayama et al. (in press) have shown that salt accumulates largely in the 0 to 0.5 cm layer of bare soil. By observing the water content at which salt accumulation reached the maximum, they determined that salt moved with liquid water at water contents as low as 0.04 volume fraction for a loam soil. For this soil the saturated water content was about 0,42 and at 15 bars it was 0.15. The 0.04 water content corresponds to a relative humidity of about 0.4. These data are supported by soil-water diffusivity measurements shown in Fig. 3. In the figure the solid circles and solid triangles represent measurements of liquid flow. Data represented by the solid circles were obtained by measuring soil-water diffusivities at several pressures (Jackson, 1965). Since water vapour flow is proportional to the reciprocal of the pressure, a plot of soil water diffusivity versus the reciprocal of pressure yielded a straight line from which the diffusivity for liquid flow was obtained by extrapolation. The solid triangles represent data obtained by placing soil columns in a chamber held at 15 bars pressure, and the open triangles represent data taken at atmospheric pressure. The solid triangles, therefore, represent liquid flow, whereas the open triangles represent the combination of liquid and vapour flow. The open circles are taken from Jackson (1964) and represent both liquid and vapour flow, with the vapour predominating. The open squares represent data for predominately liquid flow at water contents near saturation (Jackson, 1963). These data indicate that liquid flow occurred at water contents as low as 0.04 volume fraction, in support of the conclusions of Nakayama et al. (in press).

Figure 3. Soil-water diffusivity as a function of volumetric water content. Solid symbols represent liquid flow. Open symbols represent the sum of liquid and vapour flow.

Evidence that salt will move with liquid water at low water contents lends support to the concept of leaching with intermittent ponding or sprinkling. This concept of leaching is inherent in the "leaching efficiency" proposed by Boumans and Van der Molen (1964) as discussed by Bouwer (1969), described in the following section.

7.2.3. Leaching requirement and efficiency

Soluble salts are leached by applying a sufficient amount of water so that some water passes completely through the root zone. Leaching practices are determined by the quality and amount of irrigation water, the kind and quantity of salt in the soil, the ability of the soil to conduct water, and the drainage status. This requires that a leaching practice be tailored for a particular farm. A leaching practice may be to irrigate before planting with enough water to flush most of the salts through the root zone. Subsequent irrigations may be less and may allow some salt build-up. Other practices call for applying sufficient water at each irrigation to leach the root zone. A "rule of thumb" that has been used for many years is to apply a centimetre of water for each centimetre of soil to be leached. That "rule" can only apply when the irrigation water supply is ample, when adequate drainage is available and when the return flow of drainage water to the river or groundwater basin does not adversely affect the salinity of those waters.

The leaching requirement may be defined as the fraction of irrigation water that must pass through the root zone to reduce the salt concentration to a specified level. A method of calculating the leaching requirement is essential if adequate leaching with a high irrigation efficiency is to be achieved. The United States Salinity Laboratory Staff (1954) proposed a method for calculating the leaching requirement for a particular soil. Their method is well known and is at present a standard reference. Bernstein (1967) has elaborated upon their method. Bouwer (1969) proposed an alternative method of arriving at the leaching requirement.

The salt balance between irrigation water and drainage water can be expressed as

dici =ddcd

(8)


where di is the depth of irrigation water applied, dd the depth of water draining from the root zone, ci the salt concentration of the irrigation water and cd the salt concentration of the drainage water. The salt concentration terms may be expressed in terms of electrical conductivity, which is a convenient method of measuring salt concentration.

The leaching requirement (LR) is (Bernstein, 1967)

LR = ci/cd = dd/di

(9)


In practice, cd is estimated from the salt tolerance of the crop to be grown. Salt tolerance of crops is based on measurement made on the saturation extract (cse). The procedure involves preparing a soil paste by adding distilled water until a characteristic end point is reached and then extraction of some water by use of a suction filter. Salt tolerance tests usually are conducted on artificially salinized plots in which the salts are distributed more uniformly than in a field soil. Thus, the concentration of salts in the soil solution (cs) in the plant environment is not necessarily the same as in the saturation extract (cse). Different crops, for the same level of yield reduction, may have cse values that differ by a factor of ten.

Defining de as the amount of irrigation water required for evapotranspiration, the amount required for irrigation is di = de + dd.

Substituting into equation (9) and rearranging, yields

di = de/(1-LR)

(10)


which is the depth of irrigation water necessary to meet the leaching requirement.

Equation (10) applies to a soil whose infiltration rate is uniform over the entire field when water is applied uniformly over the entire field. Such uniformity is almost never found in practice and irrigators must generally apply more water than is necessary to compensate for the non uniformities. Therefore, equation (1) must be modified

di = bde/(1 - LR)

(11)


where b is the non uniformity factor. Its value usually ranges from 1.1 to 1.2. It is a factor that is best obtained by practical experience.

Boumans and Van der Molen (1964), as discussed by Bouwer (1969), stated that the salt concentration of the soil solution (cs) is not only not the same as the saturation extract (cse), but also not necessarily the same as the concentration of drainage water (cd). Using concepts similar to those discussed in the section 7.2.2: Salt and water movement, they argued that irrigation water flowing through the large channels would contain little salt and the water passing through the finer pores would contain salt in close proportion to the soil solution concentration that plants are exposed to. They considered the water draining from the root zone to be a mixture of the applied irrigation water that passed unchanged through the root zone and soil solution directly displaced by irrigation water. The fraction of drainage water consisting of displaced soil solution has been called the leaching efficiency (Bouwer, 1969 and references therein). The leaching efficiency (LE) is

LE = (cd - ci)/(cs - ci)

(12)


where cs is the salt concentration of soil-water in the root zone. The theoretical maximum of LE is one, which can be achieved only if the soil solution is completely displaced by piston flow of the irrigation water. This has nearly been achieved in column studies with structureless soils, but almost never occurs in the field. In field soils, cracks, rootholes, wormholes and other large diameter channels, plus the inherent non-uniform water application cause LE to be appreciably less than one. Field experiments (Boumans and Van der Molen, 1964) have shown that LE is about 0.2 for fine-textured soils (where cracks, rootholes, etc. may abound) to 0.6 for coarse-textured soils (where pore sizes are more uniform). For sandy soils LE may be about 0.8.

Bouwer (1969) defined the efficiency of water utilization (Eu) to be

Eu = de/di = 1 - dd/di

(13)


(the term Eu should not be confused with the water use efficiency, which expresses dry matter production in relation to water use.) Using (12) in (13) yields

Eu = LE(cs - ci)/[ci + LE(cs - ci)]

(14)


Use of equation (14) requires the assessment of irrigation water quality (reflected in ci), a knowledge of the salt tolerance of the crop to be grown (reflected in cs), and an estimation of the leaching efficiency LE. Advantages of (14) are that the value of cs is more nearly representative of the soil solution concentration for which the salt tolerance of crops has been evaluated and that LE can be estimated from the soil texture of the field to be irrigated. Bouwer (1969) tested this concept by using data from the San Joaquin and Coachella Valleys in California and for the Murray River irrigation areas in Australia. He found excellent agreement between his calculations and the published results.

The concept of leaching requirement can also be put in terms of water utilization efficiency. Using equations (9) and (11) in (13) yields

Eu = (1 - ci/cd)b

(15)


The terms LE in (14) and b in (15) are both empirically evaluated. Additional research may lead to reliable means of predicting them from soil physical and chemical principles. Field research is needed to obtain values of LE and B using optimum water management practices. Both approaches need evaluating under intermittent ponding or sprinkling leaching practices.

7.2.4 Drainage

Inherent in the previous discussions concerning water and salt movement in the soil profile was the assumption of adequate drainage, In many calcareous soils natural drainage is sufficient, but in others artificial drains must be installed to accommodate part, if not all of the drainage water. The drainage system should be designed to prevent high water tables when leaching is practiced during the growing season and should keep the water table sufficiently low between growing seasons to minimize evaporation and the consequent salt accumulation in the root zone.

Bouwer (1972a) has drawn a distinction between the terms drainage requirement and design requirement. Drainage requirement is the total drainage required for a given field or region and design requirement is the difference between the total drainage needed and the existing natural drainage. Drainage requirements have been the subject of numerous technical publications. The American Society of Agronomy is publishing their second monograph on drainage entitled "Drainage for Agriculture," which summarizes much of the latest drainage research.

Most drainage theories are concerned with a saturated system. For irrigated calcareous soils, the drainage below the root zone may be predominately in the unsaturated state. If artificial drainage is required, the design of such a system requires that the response of the water table to the influx of root zone drainage be calculated for different drain spacings, so that the optimum combination of spacing (as it affects drainage costs) and water table response (as it affects crop yield) can be selected. Calculation of water table response to root zone drainage requires that the drainage rate be known as a function of time. Expressions such as equation (5) that predict drainage below the root zone (Fig. 1) are adequate. Other equations for this purpose are discussed by Bouwer (1969).

In calculating the drainage requirement it is necessary to account for water used for leaching. Bouwer (1972b) has incorporated the concept of leaching efficiency in drainage design. Additional research concerning the application of soil water flow theory to prediction of drainage rates in unsaturated soil, including the required leaching, may improve drainage efficiency.

7.3. Management Aspects and Practices

For many years soil and water management practices were concerned only with the root zone. The quality (and often the quantity) of water leaving the root zone was of no consequence. As a result many lower areas, once productive, developed high water tables and high salt concentrations, rendering them useless for agricultural purposes. The return flow of drainage water to rivers and streams was unabated and tended to increase the salt content of irrigation waters for downstream users. Not only downstream farmers, but other interests, were affected as the competition for available water between municipal and agricultural interests increased.

One solution is the creation of salt sinks. On the farm, soil and water management practices may be implemented to store salt leached from the root zone in the vadose zone between the root zone and the groundwater table. Salts may be stored in groundwater basins in areas where these waters are not utilized. Evaporation lakes may be created to concentrate the salts. In some cases it may be necessary to construct desalinization plants to purify the water before returning it to the rivers or groundwater. Social and political pressures are causing researchers to seek new management practices on the farm, district and river basin levels.

7.3.1 Tillage practices

As noted earlier, infiltration rates can be altered by tillage. Where water movement through the soil is restricted, thus limiting the leaching of salts, deep tillage is necessary. Some soils are chiselled, slip ploughed or deep mouldboard ploughed to depths of 1.2 to 1.3 metres. Such tillage must be done when the soil is relatively dry in order to break up the impervious soil layers. Large, powerful machinery is necessary for these operations.

Sometimes the surface layers of soil are pulverized and compacted by excessive tillage. This results in a low intake rate and prolongs irrigation times. The practice of minimum tillage (Harris et al. 1965) is recommended for these conditions. Minimum tillage simply means that only those operations necessary to open up the soil for a seedbed and plant the seeds are performed. Whenever possible, chemical means should be utilized for weed control instead of cultivation.

Harris et al. (1965) measured infiltration rates in a calcareous soil to evaluate the effects of compaction by tractor wheels on a ploughed soil. They found that infiltration rates in the compacted areas were 43% of those in the noncompacted area. Low infiltration rates persisted for 2 years during which the field was cropped to alfalfa.

Minimum tillage is essential on some soils to insure adequate leaching of salts. Eric (unpublished data) has conducted studies on a silty clay soil in eastern Arizona. The irrigation water contained 2 500 to 4 500 ppm of salts, with a sodium percentage of 78%. After ploughing, with no other tillage, the soil was irrigated with 20, 30, 45 and 60 cm of water. In some instances the 60 cm treatment could not be completed because the intake rate became less than the evaporation rate. The 30 and 45 cm treatments reduced salts enough for germination to take place and a reasonable final yield was obtained. Yields of cotton, barley and sorghum were less on the 20 cm treatment. Subsequent irrigations were just sufficient to provide water for plants. Because the infiltration rates decreased after each irrigation, intermittent ponding to achieve leaching would probably not be feasible with this soil.

Although irrigated calcareous soils are susceptible to compaction by heavy equipment, some tillage is necessary. Furrow-irrigated crops are cultivated using various planting and bed shaping techniques to control the water in such a way as to lower salt content around the germinating seed. For example, cotton is planted in ridges for this purpose. First the field is furrowed and a preplant irrigation is given to leach salts. After the preplant irrigation, the top 5 cm of the ridge (containing a higher concentration of salts than the surrounding soil) is pushed to the side, the seeds are planted immediately in the same operation in the freshly exposed soil and a ridge is formed over the seed to maintain moisture. After about four days, about 5 cm of the ridge is removed to allow the sprouting plants to emerge. These operations serve to control both moisture and salts.

In some cases where the irrigation water and the soil are very salty and the land is level, seed is planted in the level soil so that the maximum amount of salt will be leached from the seedbed. If it is necessary to use furrows the seeds nay be planted in the bottom of the furrow to achieve maximum leaching from the seedbed. In such soils crusting may be a hazard; therefore, the type of seed must be considered.

Some crops such as cantalopes may require warm seedbeds. To utilize the sun's energy, planting beds are constructed sloping and facing toward the sun. To cope with salts, the seeds are planted 5 to 8 cm above the expected height of water in the furrow. This decreases crusting and allows salts to be leached up the bed slope away from the seeds.

Tillage for optimum irrigation and control of salts appears to be a fertile area for additional research. Often tillage for one purpose may be detrimental for another. Research should be geared to optimize as many factors as possible.

7.3.2 Irrigation practices

The main purpose of irrigation is to provide water to a growing crop. Yet it has been estimated that 42% of the water delivered to the farm is not used by plants for evapotranspiration (Erie, 1968). This appears wasteful until one considers that irrigation water is often applied for such purposes as to aid germination, to protect from frost, to control corn borers and caterpillars, to maintain crispness in lettuce and other vegetables during harvest, to leach salts and to dissolve fertilizers. Thus, many factors other than evapotranspiration must be taken into account by management practices. These practices must deal with how, when and how much water to apply, and the reason for the irrigation (Brie, 1968).

Many factors must be considered when selecting an irrigation method: available water, quality of water, topography, type of soil, crops to be grown and economics. Four basic irrigation methods are: basin, furrow, sprinkler and trickle or drip. With the advent of new plastic pipe and tubing designed specifically for irrigation, trickle or drip irrigation is receiving increasing attention from researchers throughout the world. This method allows excellent control of placement and amount of water. Furrow, sprinkler and trickle methods can be used on sloping lands. Furrows may be constructed on contours to reduce erosion and increase infiltration. Sprinklers, like trickle systems, may be used on almost any topography.

With sloping furrow or basin systems, field supply ditches are frequently constructed of concrete with gates installed to facilitate rapid changes of water sets. This system is readily amenable to the reuse of water on lower elevation fields. The runoff water is collected in ditches for diversion to other fields or in reservoirs at the lower ends of fields from which the water is pumped back to the higher elevations for reuse.

Basin irrigation requires the land to be level or only gently sloping. A definite trend in the southwestern United States is to construct basins "dead level." Dead-level basins usually range from 2 to 16 hectares in size and require large streams of water, usually 10 to 30 cfs (0.3 to 0.8 m3/sec), in order to cover the entire basin as rapidly as possible. Bead - level basins are perhaps the most efficient system available from the point of view of water application efficiency and salt control. There is virtually no runoff and the amount applied can be controlled accurately. This degree of control allows salts to be leached from the root zone with a minimum amount of applied water.

Runoff sediment from basins is nil; however, because of the large supply streams, erosion near the basin inlet structures can be serious. In some cases entire supply ditches have eroded away. Research has shown (Erie, unpublished data) that an energy absorber and spreading apron can be constructed of concrete in place to reduce erosion.

7.3.3 Irrigation scheduling

The timing of irrigation and the amount of water to be applied are important factors in a management programme. Significant advances have been made in the science of irrigation timing; yet, in many respects it remains an art practised successfully only through years of experience (Kyaw and Wilson, 1972). Also, the insistence of an individual farmer to make his own mistakes is a result of the scientific community not being able to 'sell" their expertise (Walker and Walker, 1972).

Frequently, more water is wasted by not knowing when to irrigate than by poor application practices. Much research has been conducted to determine the proper times to irrigate specific crops. Consumptive use estimates have been developed for many crops in the irrigated areas of the United States (Erie et al. 1965). With consumptive use data for a particular crop and a knowledge of when to give the first irrigation (pre-planting, germination, etc.) calendar dates for when to irrigate can be forecast. The forecast is appreciably better in areas where rainfall contributes little to the crop water supply. Consumptive use data for one area will not be valid for another area having widely different climatic conditions without proper conversion factors. Several methods for assessing the conversion factors have been proposed. These methods have met with various degrees of success.

An irrigation scheduling system using a computer has become relatively successful (Jensen, 1969, 1972). This system combines meteorological, soil and crop data to predict irrigation dates and amounts. The system consists of a computer programme that analyses specific fields for individual farms. Fast and predicted meteorological parameters, date and amount of last irrigation, an empirical crop factor, soil data and information from the farmer concerning management operations are entered into the programme. The computer then predicts the date and amount of the next irrigation.

This programme was revised and adapted for use by the Salt River Project in Phoenix, Arizona (Kyaw and Wilson, 1972). In addition to the computer programme the Project utilizes repetitive field checks by trained specialists. These specialists work directly with the farmer and check the soil moisture and crop status on individual fields. The combination of field checks and computerized information is intended to maximize the efficient use of water by confining water application to just that amount needed to satisfy consumptive use and leaching requirements. Another benefit of this programme is the potential for improvement of operational services. The programme can forecast the demands for actual water delivery as much as 2 weeks in advance of need. At present the Salt River Project is cooperating with the National Aeronautics and Space Administration in preliminary studies using remote sensing from aircraft as a possible tool for use in irrigation scheduling.

7.3.4 River basin salinity control

The continuous accumulation of salts within river systems has stimulated projects to reduce inflow of salt to the river (Holburt, 1972). The point source control of salts is the diverting of waters from localized salt sources such as mineral springs and outcropping of soluble formations adjacent to or underlying surface water sources, and drainage water from irrigation projects. These sources usually can be controlled, if funds are available for construction of needed structures. To carry water over formations containing soluble salts, reservoirs and impervious channels need to be constructed. Outflows from mineral springs require desalting plants to remove the salt.

Diffuse-source salt control projects have been designed to control contributions from a larger area than point source project. The basic concept is selectively to remove the saline low flows from a stream and to bypass the less saline high flows. The low flows would be desalted. The third project is irrigation-source control. Soil and water management (including irrigation scheduling) .is the key to this project. Construction and improvements of existing water conveyance systems are important also.

Computer simulation models of river basins have been devised to aid in salinity control (Hyatt, 1972) Wilson, 1972). The models describe only the basic processes in the system and have value in predicting water quality changes that might result from future development at a particular location within the river system. A computer model has also been developed to describe water and salt movement within the root zone of a crop (King et al. 1972). Models such as this should aid in the timing of soil and water management practices.

7.4. Concluding Remarks

Agricultural societies that rely on irrigation are faced with a dilemma. If irrigated agriculture is to continue, the salt concentration in the root zone must be kept low. If this is done, the quality of return flow water to rivers and groundwaters is degraded by the increased salt content. On the other hand, this degradation can no longer continue. Good quality return flow must be maintained in order to serve other essential elements of the society.

To maintain good quality return flow water by having neither leaching to ground - water nor runoff presents a formidable challenge to agricultural research. Future management practices should use water to the maximum of efficiency and move salts below the root zone to be stored between the bottom of the root zone and the top of the capillary fringe above the water table. To accomplish this goal, additional research is required in areas such as water movement into and through soil, water use efficiency, consumptive use of water by crops, salt tolerance of crops, removal of salts by precipitation in insoluble forms, leaching requirement or efficiency, and irrigation structures.

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Brie, L.J., French, O.F. and Harris, K. 1965, Consumptive use of water by crops in Arizona. Univ. of Arizona Agr. Expt. Sta. Tech. Bull. 169. Tucson, Arizona.

Evans, D.D., Kirkham, D, and Frevert, R.K. 1951, Infiltration and permeability in soil over-lying an impermeable layer. Soil Sci. Soc. Am. Proc. 15:50-54.

Harris, K., Erie, L.J. and Fuller, W.H, 1965, Minimum tillage in the southwest. Univ. Arizona Agr. Expt. Sta. Dull. A-39.

Holburt, M.B. 1972, Salinity control needs in the Colorado River basin. Proc. Ntl. Conf. on Managing Irrigated Agriculture to Improve Water Quality. USEPA and Colorado State Univ. pp. 19-25.

Hyatt, M.L. 1972, Modelling salinity in the upper Colorado River basin. Proc. Ntl. Conf. on Managing Irrigated Agriculture to Improve Water Quality. USEPA and Colorado State Univ. pp. 215-227.

Jackson, R.D. 1963, Temperature and soil water diffusivity relations. Soil Sci. Soc. Am. Proc. 27:363-366.

Jackson, R.D, 1964, Water vapour diffusion in relatively dry soil: I. Theoretical considerations and sorption experiments. Soil Sci. Soc. Am. Proc. 28:172-176.

Jackson, R.D. 1965, Water vapour diffusion in relatively dry soil: IV. Temperature and pressure effects on sorption diffusivities. Soil Sci. Soc., Am. Proc. 29:144-148.

Jensen, M.E. 1969, Scheduling irrigations using computers. J. Soil and Hater Conservation. 24:193-195.

Jensen, M.E. 1972, Irrigation scheduling in Idaho. Proc. Ntl. Conf. on Managing Irrigated Agr. to Improve Water Quality. USEPA and Colorado State Univ. pp. 181-185.

King, L.G., Hanks, R.J., Nimah, M.N., Gupta, S.C. and Backus, R.B. 1972, Modelling subsurface return flows in Ashley Valley. Proc. Ntl. Conf. on Managing Irrigated Agr. to Improve Water Quality. USEPA and Colorado State Univ. pp. 241-256.

Klute, A. 1972, The determination of the hydraulic conductivity and diffusivity of unsaturated soils. Soil Sci. 113:264-276,

Kyaw, E.W. and Wilson, D.S, 1972, Irrigation scheduling in the Salt River Project. Proc. Ntl Conf. on Managing Irrigated Agr. to Improve Water Quality. USEPA and Colorado State Univ. pp. 187-194.

Nakayama, F.S., Jackson, R.D., Kimball, B.A. and Reginato, R.J. Diurnal soil-water evaporation: Chloride movement and accumulation near the soil surface. Soil Sci. Soc. Am. Proc. (Submitted).

Nielsen, D.R., Biggar, J.W. and Corey, J.C. 1972, Application of soil-water flow theory to field situations. Soil Sci. 113:254-263.

Nielsen, D.R., Biggar, J.W. and Miller, R.J. 1964, Soil profile studies aid water management for salinity control. California Agriculture, August. pp. 4-5.

Oster, J.D., Willardson, L.S. and Hoffman, G.J. Sprinkling and ponding techniques for reclaiming saline soils. ASAE Trans. (in press).

Philip, J.R. 1957, The theory of infiltration: 4. Sorptivity. and algebraic infiltration equations. Soil Sci. 84:257-264.

Rose, C.W. and Stern, W.R. 1965, The drainage component of the water balance equation Aust. J. Soil Res. 3:95-100.

U.S. Salinity Laboratory Staff. 1954, Diagnosis and improvement of saline and alkali soils. Handbook 60, U.S. Dept. of Agr.

Van Bavel, C.H.M., Stirk, G.B. and Brust, K.J. Hydraulic properties of a clay loam 1968 soil and the field measurement of water uptake by roots: I. Interpretation of water content and pressure profiles. Soil Sci. Soc. Am. Proc. 32:310-317,

Walker, W.R. and Walker, W.R. 1972, Surviving with salinity in the lower Sevier River Basin. Proc. Ntl. Conf. on Managing Irrigated Agr. to Improve Water Quality. USEPA and Colorado State Univ. pp. 257-263.

Watson, K.K. 1959, A note on the field use of a theoretically derived infiltration equation. J. Geophys. Res. 64:1611-1615.

Whisler, F.D. and Bouwer, H. 1970, Comparison of methods for calculating vertical drainage and infiltration for soils. J. of Hydrology 10:1-19.

Wilson, R.F. 1972, Hydrologic modelling of Ashley Valley, Utah. Proc. Ntl. Conf. on Managing Irrigated Agric. to Improve Water Quality. USEPA and Colorado State Univ. pp. 229-239.

DISCUSSION

The question of the use of bitumen as a treatment to reduce soil crusting was raised. Bitumen may be sprayed on a small area directly over the seed after planting or as a band over the seed row. In addition to reducing crusting the black material increases the absorption of solar radiation and therefore soil temperature. It also reduces evaporation of water. These factors improve the seed environment. Experiments have shown the feasibility of this treatment but it has not been generally adopted as a management practice.

A question was raised concerning what chemical reactions occur when H3PO4 is sprayed on the soil surface to reduce crusting. The question was not resolved.

The method of "dead level" irrigation was discussed. This type of irrigation is usually carried out on soils that are relatively flat and do not require excessive levelling. The length of run in such a system depends upon the type of soil, the quantity of available water and the means of applying this water rapidly.

Pan evaporation as an indication of when to irrigate is used in some countries in the Near East. This method is used to some extent in the U.S.A. but is not the predominant one. Consumptive use studies and a computer based system are being used to a larger extent.

The possibility of using remote sensing techniques to determine soil moisture status was discussed. Infra-red and microwave radiometers are being tested in the United States to ascertain their usefulness. The method is in the early stages of testing and it is too early to say how successful it will be.

8. Irrigation and Drainage Practices of the Organic Calcareous Soils in the Ghab Project in Syria

by

A. Arar
Regional Land and Water Development Officer
FAO Regional Office, Cairo, ARE

8.1. Introduction

The Ghab Valley is situated in the north-west of Syria and in the lower part of the Orontes Basin. The Valley is about 50 km long and with an average width of about 10 km. Before reclamation the greater part of the Valley was occupied by perennial and seasonal marshes. The project for the reclamation and agricultural development of the Valley was, therefore, first and foremost a drainage project. After the construction of the main irrigation and drainage network, the net irrigable area was about 43 000 ha, out of which about 26 000 ha was under marshes. The average rainfall which falls during the winter season (October-April) increases from 600 mm in the south-east to about 1 000 mm in the north-west giving an average of about 800 mm for the whole Valley. In view of this, the Valley is rather wet during the winter months which requires drainage to get rid of the excess rainfall. On the other hand, during the dry hot season of the summer months (May-September) irrigation is necessary for the production of perennial and summer crops.

The Ghab has been a lake at different times and the sediments in this lake form a continuous cover on the bottom of the depression. The lower deposits are of about 100 to 200 m thickness and consist of sandy marls and chalky marls which are relatively impervious. The upper sediments are of a more recent origin and belong to the end of the Pliocene and Quaternary and partly of recent origin. They are composed of relatively impermeable grey plastic marl of lacustrine origin. Their thickness is more than 40 m. The most recent and present day deposits consist of alluvial deposits, hillside wash, recent and present day river levees, recent and present day marsh and lake deposits and lakeshore deposits. These deposits form the parent material of the different agricultural soils in the area. It becomes clear that nearly all the soils of the irrigable land in the Ghab Valley are undifferentiated alluvial and lacustrine soils.

As mentioned above, more than 50% of the Ghab Valley was either perennial or seasonal marshes. The main characteristic of these soils is their high content of organic matter, whereas under the climatic conditions of the region, the equilibrium of the organic matter content of a normal well drained soil is about 2%. Before draining the area, the Ghab perennial marshy soils had an organic matter content ranging from 8 to 45%. Ever since the marshes disappeared, after the construction of the main drainage network the oxidation of the organic matter took place rather fast. At present, the average organic matter content is from 5 to 10%.

8.2. The Organic Calcareous and Marly Soils of the Ghab Valley

Strictly speaking, all the soils of the Ghab Valley could be called calcareous soils because the calcium carbonate content is not less than 20% for any soil type.

However, for our present purpose, we will discuss only two soil types which have a calcium carbonate content of more than 60% and which belong to the soil series of the perennial marshes. In the perennial marshes, the peat is formed by the growth of higher plants such as carex and reed in shallow and moderately deep water respectively. In deep water, only primitive plants such as characae diatoms and other monocell plants can thrive. These plants have the characteristics of accumulation of CaCO3 in their tissues and gave rise to the lacustrine marls.

Broadly speaking, there are two types of soils; one type which is the most widely spread is highly calcareous soils overlaid by powdery humic substance. These soils are light to medium-textured loamy soils characterized to very high calcium carbonate content (60 - 80% CaCO3). The other type is marly soil with calcium carbonate content of more than 70% and organic matter of about 5% They are powdery and dusty when dry and without any cohesion. If worked wet, they dry out to hard blocks. From the physical point of view, these soils are very poor with a low clay content and the water holding capacity is low (about 14%). From the chemical point of view, they should be considered as poor, except for the fact that they have a relatively high organic content of 5 to 10% which will eventually be reduced to about 2% as mentioned before, if certain precautions are not taken. The following is a typical analysis of these soils:

(1)

Physical Properties

Marly Soil

Organic Calcareous Soil







Sand

60%

40%

Silt

25%

50%

Clay

15%

10%

Wilting Point

15%

20%

Water Holding Capacity

30%

34%




(2)

Chemical Properties







Organic Matter

51%

8%

Total Nitrogen

0.40%

0.45%

P2O5

50 ppm

75 ppm

CaCO3

75%

65%


8.3. General Remarks on the Management of the Ghab Calcareous Soils

As mentioned before, the top humic layer was classified before drainage as peat (about 40% organic matter), it has dropped to about 8% after about 10 years of drainage. It can be concluded that under the prevailing climatic conditions (summer mean average temperature of 26°C) and cultural practices, the organic matter content may reach in future an equilibrium value of 2% as is the case in normal and well drained soils in the region.

The answer to the question how long it will take to reach this equilibrium value will depend on the management of these soils. The soil fertility problem, at present, does not look so serious, thanks to the nutrient release from the organic matter reservoir. The decomposition and depletion of this reservoir may create a serious problem in the future especially where this humic soil is overlying a highly calcareous sub-soil. To delay the decomposition of the powdery humic substance of the top soil and also the bands of organic matter which are found frequently imbedded in the soil profile at different depths up to 150 cm, certain precautions should be taken. Beside keeping the soil moist as long as possible by the proper irrigation and drainage practices, which will be the subject of this paper, other items such as the minimum disturbance of the soil surface through ploughing and cultivation and the protection of the top soil from wind erosion by keeping the crop stubble together with the use of windbreaks. Another alternative is to plough in the top humic soil with the marl below. It is argued that due to the fact that the clay minerals in the marl are mainly of montmorillonite type, which has the property of preserving the organic matter, and this ploughing in of the top humic layer with the marl below, will help to conserve the organic matter for a longer period of time.

8.4. Irrigation of Calcareous Soils of the Ghab

8.4.1 Basin Irrigation

Basin irrigation is the predominant method of irrigation in the Ghab and will probably continue for some time to come. When practised correctly, it could be an efficient method of water application, provided that the required labour is available to guide the water carefully from basin to basin. Because of high infiltration rate and no soil levelling, small basins of about 5 m × 7 m are used at present. The depth of irrigation varies from 150 to 200 mm and not more than 50% of irrigation application efficiency is obtained. Larger sizes of basins could be used and with higher application efficiencies. Simple land floating will be sufficient in most cases. Only in a few places, movement of the earth by tractors and scrapers followed by large land planes for finishing the grade will be required. Every two or three years, land which is cropped yearly should be land planed in order to obliterate the microrelief which will develop with standard cultural practices and to land subsidence through sub-soil shrinkage due to drainage and oxidation of the organic content of soil. The main objections to basin irrigation are its requirement of high labour, obstacle to mechanization and the loss of a good percentage of land for ditches and levees.

8.4.2 Sprinkler and Drip Irrigation

The soil infiltration rate of these soils is very high as it ranges between 8 cm to 20 cm/hr. Under such conditions, sprinkler or drip irrigation seem to be the most suitable irrigation methods. However, due to the high velocity of the wind which could be more than 5 m/sec and to the erratic nature of the winds the use of sprinklers is precluded over much of the area. The high cost of capital investment (300 - 1000 Syrian Pounds/ha) and the operation and maintenance of sprinklers introduce a limiting factor to their extensive use in the Ghab. Sprinklers may be satisfactory in wind-sheltered areas for the production of high value speciality crops.

Drip irrigation could be used to advantage in the high infiltration soils with high wind velocities. This method of water application is a relatively new one and its cost is expected to be quite high ranging from 1 000 to 1 500 Syrian Pounds/ha. Nevertheless, it may be well worth-while to carry out field experiments on this method of irrigation under the Ghab conditions which may prove to be suited for row crops of high cash value.

8.4.3 Sub-Irrigation

These soils form the bottom areas of the Ghab Valley. Where large blocks of single crops are grown on them, a system of sub-irrigation could be practised more intensively than at present. By manipulating the water in the drain ditches, a raising and lowering of the water table could be practised in order to saturate the soil profile to the depth of rooting of the crop and then by releasing the water, to allow the profile to drain to field capacity. This method of irrigation requires care in grading the land and in manipulating the water table.

In every method of irrigation, a degree of land grading is necessary, the greatest accuracy is required for sub-irrigation and for surface methods in which the ground surface is used to convey water.

8.5. Drainage of the Calcareous Soils

8.5.1 Optimum depth of underground water table

A lysimeter experiment was carried out in the Ghab Project in 1967-1970. The main objective of this experiment was to find out the optimum depth of underground water table in relation to yield of crops and the economy of irrigation water.

8.5.1.1 Effect of underground water depth on crop yields

The effect of underground water depth on crop yields was studied in the Ghab with two different soil types (light organic calcareous soil and heavy clay soil) using different static depths of underground water ranging from 30 en to 120 cm using lysimeters. The crops included in this study for the light organic calcareous soil were cotton and alfalfa. The summary of these results is indicated in Table 1.

Table 1. Effect of underground water depth on crop yield in lysimeters in organic calcareous soil - figures are % of maximum yield

Crop


Depth of Water Table in cm Below Ground Surface

30

40

50

60

70

80

90

100

110

120

Cotton

-

55

-

100

-

90

-

85

-

65

Alfalfa


1st Year

76

-

80

-

100

-

94

-

83

-

2nd Year

53

-

70

-

81

-

80

-

100

-


From the above table, it can be seen that maximum yield of cotton in light organic calcareous soils was obtained at about 60 to 80 cm depth of water table. In the case of alfalfa, maximum yield was obtained at water table depth of 70 cm in the first year, but in the second year it increased to 110 cm.

8.5.1.2 The effect of water table depth on its contribution to the root zone

The kind of crop grown and its stage of development and type of soil all have an influence on the amount of water that can be extracted from the water table. The summary of these results is shown in Table 2 below.

Table 2. Water table contribution as % of total consumptive use of crops in lysimeters in organic calcareous soils

Crop


Underground Water Depth in cm

30

40

50

60

70

80

90

100

110

120

Cotton

-

70

-

52

-

35

-

28

-

13

Alfalfa


1st Year

78

-

65

-

53

-

51

-

41

-

2nd Year

80

-

70

-

60

-

55

-

47

-


From Table 2, it can be noted that cotton was extracting about 50% of its requirement from the water table at a depth of 60 cm, but this contribution declined rapidly with increasing water table depth, as it was only 13% of the total at a water table depth of 120 cm. Alfalfa was more active than cotton in this respect and it improved its performance during its second year as compared with the first year. Alfalfa was still extracting about 50% of its total requirement from the water table at a depth of 90 cm during the first season and nearly the same percentage at a water table depth of 110 cm during the second season. This indicates that the contribution of water table to the crops is effected to a great extent by the activity of the root system, of the plant itself.

From the above discussion it could be concluded that the optimum depth of water table in light organic calcareous soils in relation to yield of crops and the economy of irrigation water is about 70 cm for cotton and 100 cm for alfalfa, giving an average water depth of 80 to 90 cm for the project as a whole.

8.5.2 Optimum depth of field drains

The optimum depth of field drains is governed by several factors, the most important of which are the cost of construction, the hydrological properties of the soil profile and the optimum depth of underground water to be maintained. The latter is governed by the yield of the crops, the salinization hazard and the utilization of water from the water table by the crops and hence, the economy of irrigation water use.

The cost of construction of field drains with the available machinery on the market does not increase noticeably from 1.0 to 1.8 meters. Beyond 1.8 meters much heavier machinery is needed and cost increases rapidly.

The study of the hydrological properties of the soil profile indicated that the top 2 to 2.5 metres of the soil profile of these calcareous soils is of high permeability of about 10 to 12 m/day.

Below this depth there exists a nearly impermeable layer of grey marl which, as has been indicated before, extends for a thickness of several hundred metres. Consequently, it is important that field drains should never be placed in this impermeable layer of grey marl.

The studies on the optimum depth of underground water which has been discussed before, indicate that the optimum depth of water table seems to be around 80 to 90 cm in the light organic calcareous soils and marly soils.

As mentioned before, these calcareous soils have a high infiltration rate which means that by the use of the conventional surface irrigation methods, a large portion of the irrigation water will be lost during irrigation to the water table. At present, with the use of small irrigation basins, but without land smoothing, the depth of the irrigations ranges between 150 to 200 mm and with irrigation application losses of more than 50% Even with land smoothing and the use of other methods of surface irrigation (furrows or borders), this situation could not be improved very much. The use of sprinkler or drip irrigation which is most suitable for these types of soils is not likely to be carried out on a large scale in the Ghab project for many years to come. This is mainly because of the high capital, operational and maintenance costs of such systems. Consequently, it is expected that high losses of irrigation water to the water table will continue and every effort should be made to utilize some of this lost water. This could partly be achieved by keeping the water table relatively high so that crop roots could extract some of their requirements from the water table.

Due to the heavy winter rainfall in the Ghab, which amounts to about 600 mm in the south and 1 000 mm in the north and with an average of 800 mm, sufficient leaching is provided so the problem of soil salinization by capillary action from shallow water table should not arise once the necessary field drainage network is installed.

Taking all the above factors into consideration, and remembering that most of the crops in the Ghab will consist of cotton, alfalfa, sugar beet and vegetables, it seems reasonable to conclude that the optimum average depth of the field drains in the Ghab should be in the region of 130 cm in the organic calcareous soils and marly soils.

8.5.3 Spacing of field drains

To estimate the spacing of field drains, it is necessary to determine first the following:

1) the drain depth
2) the drainage criteria
3) the hydrological properties of the soil profile; and
4) the formula to be used in calculating drain spacing.
8.5.3.1 The optimum depth of field drains

As has been discussed before, and after taking into consideration all factors concerned, it was concluded that the optimum depth of field drain should be about 130 cm below the ground surface.

8.5.3.2 The drainage criteria

The drainage studies in the Ghab for several years have indicated that the drainage criteria should be based on the control of water table during the winter rainy season. The drainage criteria which have been adopted and which are based on the results of field drainage experiment and on the analysis of the quantities and distribution of winter rains for the organic calcareous soils and marly soils are as follows:

i) Drainage runoff of 8 mm/day with water table 50 cm below the ground surface in the north-west of the Ghab

ii) Drainage runoff of 6 mm/day with underground water table 50 cm below the ground surface in the south-east of the Ghab.

It should be mentioned here that the drainage intensity based on the above-mentioned drainage criteria is more than sufficient to maintain a favourable salt balance in the soil under the Ghab climatic conditions. It is also quite satisfactory to control the fluctuation of underground water table which will be caused by the high irrigation losses, mentioned before, within safe limits for the development of agricultural crops. This is understandable for several reasons: firstly, the irrigation water available during the summer months is only sufficient for half the area; secondly, the irrigated area is not concentrated in very large blocks due to the fact that the size of the individual holdings is only about 2.5 ha. Thirdly, in addition to this, the irrigation cycle extends for about 3 weeks. Furthermore, this has also been confirmed by field observations of underground water levels and discharges of field drains for four irrigation seasons, in light organic calcareous soils at Ain El Naour Drainage Experimental Farm.

8.5.3.3 The hydrological properties of the soil profile

In the case of the organic calcareous soils, the top soil profile of about 2.5 metres deep has an average permeability of 12.0 m/day. Below this, the marly formation starts (grey plastic marl) with very low permeability of about 10 to 20 cm/day. For practical purposes this marly formation, which extends for several hundred metres, can be considered impermeable.

Regarding the marly soil, the top soil profile of about 2.0 metres thickness has an average permeability of about 10 m/day. Like the above soil type, the grey marly formation starts at about this depth

8.5.3.4 The formula to be used in calculating drain spacing

It was found that the steady state flow formula of Hooghoudt gives very satisfactory results and corresponds well with the drainage experimental results. This formula is as follows:

Where:

L = Drain spacing in metres

q = Drain discharge in metres per day

K1 = Hydraulic conductivity of the soil layer above the drains in m/day

K2 = Hydraulic conductivity of the soil layer below the drains in m/day

h = The height of the water table above the drain level midway between the drains in metres

d = Thickness of the equivalent layer. This depends on the drain spacing (L), the drain radius "r" and the depth of the impermeable layer “D” below the bottom of the drains in metres. Under the Ghab conditions, the value of "d" is nearly equal to "D". See paragraph 8.5.3.5. later on.

Visser's formula was also used and gave nearly the same figures obtained by Hooghoudt's formula. The Visser formula applicable to the Ghab conditions is the following:

1: h, q, L and K are the same as those mentioned above in Hooghoudt formula
2: Do = The depth of the impermeable layer below the water level in the drain in metres
3: D1 = Do + 0.5h
4: Ln = Natural Logarithm (e)
5: u = The wet perimeter of the drain in metres
6: p = 3.14
8.5.3.5 Summary

It is now possible to calculate the drain spacing after deciding on the drainage criteria, the soil hydrological properties and the depth of the field drains. The following Table 3 summarizes all the parameters which should be used in the Hooghoudt formula to calculate the field drain spacing for the calcareous soil groups in the south- east and north-west of the Ghab. The depth of the permeable top soil above the impermeable dark grey marl has to be found by investigation in the field. The calculated drain spacing in the following table is based on the depths of 2.5 m and 2.0 a for the organic calcareous and marly soils respectively.

Table 3.

Parameters

Soil Drainage Group

Organic Calcareous

Marly

1. Average depth of impermeable layer-m

±2.5

±2.0

2. Permeability of the top soils profile m/day (K.)

12.0

10.0

3. Depth of field drain-m

1.3

1.3

4. Depth of Decatering Zone-m

0.5

0.5

3. Head of water (h) in m

0.8

0.8

6. Approximate value of "d"-m

1.18

0.70

7. Drainage runoff (q) in mm/day





i. South-east of the Ghab

6

6

ii. North-west of the Ghab

8

8

8. Calculated Drain Spacing in Metres (Hooghoudt formula)





i. South-east of the Ghab

140

110

ii. North-west of the Ghab

125

95


From the above table, it could be noted that with field drain depth of 130 cm the spacing of field drains in the organic calcareous soil and marly soil is 140 and 110 metres respectively in the south-east of the Ghab. In the north-west, where rainfall is heavier, the spacing dropped to 125 m and 95 m for the organic calcareous soils and marly soils respectively.

8.5.4 Types of field and collector drains

Drains can be either of the open or covered type. From the functional point of view, there is very little to choose between open drains and well constructed covered drains. Hence, the choice of using one type or the other is governed by economical and practical considerations which can be summarized as follows

1) It is generally an accepted fact that the main objection to the use of covered drains as opposed to open drains is the higher construction cost of the first. In view of the recent developments in the construction of covered drains by using tile making machines and tile laying machines, this point is no longer an accepted fact. Under the prevailing conditions in the Ghab Valley in Syria, the cost of covered field drains, using machine made concrete tiles of 10 cm inside diameter, and a tile laying machine, is less than cost if the same drains were made open type with the proper side slopes.

2) Other points are all in favour of covered drains as opposed to open drains. The covered drains are much cheaper to maintain. Experience in different countries has shown that the maintenance cost of covered drains is only 20 to 40% of that of open drains. The maintenance problem of the open drains under the Ghab project is a big one. Beside the usual sedimentation and the growth of weed, there is the problem of wind blown light material. This is not to speak of the erosion caused by rainwater and excess irrigation water which erode the sides of the open drains. Blocking the drains by earth to make crossing for human beings, animals and even cars and agricultural machinery is still another administrative and maintenance problem.

3) By the use of covered field and collector drains about 5 to 10% of the surface area, which is the best drained land, will be saved for agricultural purposes. To this one has to add that with covered drains it will be possible to have larger fields and hence a better utilization of the mechanization possibilities. The problem of crossings for field roads and also for irrigation water courses will not arise in case of the use of covered drainage which will mean a further saving in the project construction cost.

4) The possibility of having a breeding place for malaria mosquitoes in the open water courses, especially if they are not well maintained, is still another point against open drains. However, it must be mentioned here that the operation and maintenance of covered drainage system, requires more qualified staff than that required for the open drainage system, so as to be able to observe points of failure which are covered and to locate such points and to put them right. It is quite easy, however, for such a job to be done by a drainage engineer or even by secondary school graduates after a few months training.

5) To maximise the efficient use of irrigation water, it is possible by the manipulation of the water in drain ditches to raise and lower the water table level in the fields. This practise could be carried out with great care in case of occasional shortages of surface irrigation water. The covered system of drainage network in most cases will be more convenient for this purpose than the open drainage system.

Because of the above reasoning, it has been decided that field and collector drains in the Ghab are to be constructed of the covered type.

REFERENCES

Arar, A. 1968, Problems of Salinity and Drainage in the Ghab. Drainage and Salinity Study Series, Report No. 9, UNSF Ghab Project, Syria.

Arar, A. 1969, The Effect of Underground Water Depth on the Yield and Water Consumption of Cotton. Drainage and Salinity Study Series, Report Ho. 10 UNSF Ghab Project, Syria.

Arar, A. 1972, Summary Report on Drainage Work, Drainage and Salinity Study Series. Report No. 11, UNSF Ghab Project - FAO Regional Office, Cairo.

Cavelaars, J.C. 1970, Report on Consultant Mission, UNSF-FAO Ghab Development Project. Ilaco, Arnhem, Netherlands.

Houston, C.E. and others. 1971, Report on Duty Travel to Syria. 25-29 September 1971. AGLW; FAO, Rome.

NEDECO, 1953; Avant Project El Ghab. Den Haag, The Netherlands.

9. Reclamation and Management of the Calcareous Soils of Egypt

by

H.E. Dr. M.M. Elgabaly
Minister of Agriculture and Land Reclamation - Egypt

Honourable delegates, it gives me a great pleasure to talk to you on the subject of reclamation and management of calcareous soils in Egypt. As a matter of fact, land reclamation activities in this country include the reclamation of salt affected soils, sandy soils and calcareous soils and I am going to confine my lecture to the last one.

9.1. Definition

Calcareous soils, as we define them, are those soils containing amounts of calcium carbonate to affect distinctly the soil properties related to plant growth, whether they are physical, such as the soil-water relations, and crusting, or chemical such as the availability of plant nutrients.

9.2. Distribution

The calcareous soils which are under reclamation are mainly found to the west of the Nile Delta in a strip extending from Alexandria to Lybia. The soils along the Mediterranean Sea coast are formed as a result of wave and wind action. They have the specific characteristics of Oolitic sand dunes. The lime content may reach up to 95 percent. Due to the wave action, these dunes are pushed inland to form ridges that solidify to various degrees as a result of rainfall, solution and redistribution of carbonates. These ridges, upon weathering, form calcareous soils which are transported by water or wind to the internal ridges and plateau until they connect with the Delta. Consequently, the lime content gradually decreases from 95% along the coast to 4% in the Delta. Although the Delta soils contain 3 to 4 per cent CaCO3, we do not refer to them as calcareous soils since no specific effect is noticed on their physical or chemical properties due to CaCO3. Generally, the CaCO3 content of the Egyptian calcareous soils under reclamation varies between 10 to 90% but mostly between 10 and 50%.

9.3. Morphologic Characteristics

The morphology as well as other characteristics of these soils are functions of topography and micro-relief The topographic features of the area start with the sea coast followed by two ridges with a depression in between and finally a plateau extending to the Nile Delta. Taking this into account, knowing that the soils are mostly residual, and considering the effective soil forming factors in this region, we find that soil erosion, firstly by water and secondly by wind, is the main effective factor leading to the formation of different soils. On this basis, it is possible to classify these soils into three main categories according to depth of profile, percentage of CaCO3, and depth to the calcium carbonate horizon and its thickness.

The soils on the ridges are shallow and have no definite horizons. The depth of the profile may be zero, where the surface is eroded by wind, or may reach up to 50 cm. The profiles of the medium deep soils vary from 50 to 100 cm while those of the deep ones are greater than 100 cm. The variation in the soil depth between these three categories is gradual and no definite boundaries exist between them. The formation of this toposequence repeats itself all over the area from the deep soils at the centre of the depressions to the shallow soils on the top of the ridges.

From the stand point of the lime horizon and lime content, we find that the soils on the ridges have no definite lime horizon but the lime content is usually much higher than in medium or deep soils. The lime horizon of the medium deep soils is generally close to the surface and generally does not exceed 20 or 30 cm. In some cases, it may be clearly defined and in others diffused. In the deep soils, the lime content is generally less throughout and two types of profiles can be identified in the first, a clearly defined horizon is found diffused in a layer that may reach 30 cm thick and in the second type the lime accumulation horizon may not be clear at all It has been found that the formation of the lime horizon is related to the micro-relief, the moisture relations and the soil permeability. In areas where the accumulated amount of rainfall is large and the permeability is high the lime horizon does not show itself. But if the internal water movement is limited, due to low permeability and surface runoff as affected by the micro-relief, then the accumulation horizon becomes well defined.

The texture of these soils is usually coarse on top of the ridges and becomes finer as we move downward to the depressions.

In some of these soils, a gypsum hardpan may be formed at the bottom of the depressions. The origin of this gypsiferous horizon may be pedologic or geologic and its depth varies with the water and salt movement depending upon whether it results from the groundwater or the reaction with sea water

From intensive studies on the clay minerals of the calcareous soils in this region we have found that the dominant mineral is attapulgite mixed with a small amount of kaolinite and montmorillonite.

9.4. Reclamation and Management

A detailed soil survey, prior to reclamation, was carried out by various institutions (the Desert Institute, the Land Reclamation and Development Institute, the Soils Department of the Ministry of Agriculture and the High Dam Authority). The soils are mainly calcareous loams and in part of the area they are calcareous sand at least in the surface horizon. In those soils covered with sand, the subsoil is quite similar to that of calcareous loamy soils. These soils have been subjected to submergence by sea water and have similar characteristics and type of clay minerals as those previously mentioned.

Since our experience in reclaiming calcareous soils was rather limited, we started with studies on their water relations, fertility and chemical characteristics. .

9.4.1 Soil water relationship

The soil water relationship was the first problem faced but through intensive research we were able to learn more about the behaviour of these soils under irrigation. The available moisture range is not more than 10 to 12% as an average. Milting occurs at 9 to 10% while the field capacity is 19 to 21%. Comparing these soils with the clay soils of the Delta we find in the latter that wilting occurs at about 16% the field capacity is about 36 to 37% and the available moisture range is about 23%. From various studies it has been found that most of the available water is utilized before or even at a moisture tension of one atmosphere ,while in the Delta soils this may occur at a tension of 4 atm.

Since most of the lime is in the silt fraction, one would expect that the ability of these soils to retain moisture would be rather limited. The studies have revealed that most of the water is being held by physical forces and that is why the decrease in the available moisture occurs rather abruptly and not gradually as is the case in the alluvial soils of the Delta. Of course, these moisture characteristics are very much related to the efficiency and frequency of irrigation.

9.4.2 Surface crusting

Another basic problem was that of surface crusting. It is known that the organic matter content of these soils is not more than 0.4% and it is usually much less than this. Before putting these soils under irrigation for the first time they possess apparent good physical conditions, but as soon as they are irrigated chemical changes occur. Solution of carbonates to bicarbonates and the precipitation of the latter upon drying assist in the formation of a hard surface crust which is also affected by the texture and the dominance of other salts beside the CaCO3. In the presence of Na salts the formation of this crust is not so obvious and it breaks off easily. Its thickness may vary from a few centimetres to more than 20 cm in some cases. Since crusting was one of the main problems that faced agriculture, especially in the early stages of development, studies were carried out on soil, water and crop management practices to reduce the effect of this phenomenon.

9.4.3 Land levelling

Land levelling was a third major problem that we were faced with in reclaiming these soils. The topography is not flat as is the case in the alluvial soils but is mostly undulating with a slope which may sometimes reach 5%. Because the slope does not follow a single direction, putting these soils under irrigation would require their levelling in a certain direction. How can this be done without ruining the soil properties and in particular without removing the top surface, which may be relatively highly fertile or exposing the lime horizon to the surface, which is the worst thing that can be done.

Studies have been undertaken to find out the appropriate methods of irrigation, dimensions of the plots, surface slopes and degree of levelling. No general specifications could be worked out but the specific nature of these soils had to be taken into consideration. A detailed soil survey could be very helpful in this regard and a scale of 1: 2 500 is the most appropriate. It is worth mentioning that the inaccuracy of land levelling has led to numerous mistakes in our utilization of these soils.

9.4.4 Irrigation methods

The selection of an appropriate irrigation method was the fourth problem. Egyptian farmers are used to surface flooding irrigation of their flat and extensive lands without harmful effects to their soils when supplied with adequate drainage. But for the newly reclaimed calcareous soils which are characterized by the previously described topographic features and by the difficulty in levelling them, a more suitable method of irrigation must be found.

Taking these limitations into consideration, contour irrigation could have been appropriate for these soils. The method was applied on an experimental basis and it was possible to determine the design criteria such as the length of run, slope and rate of discharge to give the best moisture distribution in the root zone along the length of run. Unfortunately, the contour irrigation method as well as contour farming, both being new to the Egyptian farmer, were not easily accepted for application. The method was modified and the land was levelled. Consequently, problems of secondary salinization and low irrigation efficiency became apparent.

In fact, contour cultivation could and should have been generally used in this area since it had been practised by the Romans under rainfed agriculture where the rainfall was collected in the depressions for winter crops and the soil fertility was kept high.

9.4.5 Soil cultivation

The methods of soil cultivation adopted differ from those practised in the Delta soils which are homogenous, low in carbonate content, have higher amounts of organic matter and a physical condition which is favourable for root extension. The calcareous soils quickly change their favourable properties when irrigated. They become indurated and resistant to root penetration especially in that portion of the profile subjected to wetting and drying. Therefore, the depth of ploughing is one of the important factors in relation to the success or failure of growing crops.

Different ploughing techniques and ploughs were tried. The results indicate that the optimum depth should not be less than 20 cm, and preferably 25 cm, using a mouldboard plough followed by a chisel plough in a perpendicular direction. The moisture content at the time of ploughing should be adequate in the ploughing depth to ensure a good soil structure. It has been found that the optimum moisture range for ploughing is very narrow and occurs within 4 to 5 days of irrigation, but after 7 or 8 days ploughing becomes difficult. Therefore for the successful ploughing of these soils it is essential that it should be carried out within a short time. Unfortunately, it is rather frequent that a lack of awareness of these principles leads to serious problems.

9.4.6 Suitable crops

The classical crops grown on the Delta soils such as cotton, wheat, maize and sugar cane, were the first it was thought of growing on the calcareous soils but all failed except maize. Cotton failed to grow on these soils because of physical, chemical and nutritional factors and even the normal morphology of the plant changed and became different from the Egyptian cotton. He have to think of lime-loving plants and for this reason legumes occupied first priority (alfalfa, Egyptian clover, peas and beans). Beans did not succeed as well as could have been desired due to the effect of wind and other environmental factors. At least alfalfa and other kinds of berseem proved to be successful. That is why they occupy about 33% of the cropping pattern on these soils. But the main problem of these crops is their high water requirements and the subsequent secondary salinization in the low lying fields.

To avoid the problems arising from high water applications, we have had to think of other lime-loving crops which require less water. From experience, we have found that vines satisfy these requirements (5 000 m3/ha) followed by almonds and olives. Fruit trees occupy 33% of the cropping pattern with vines constituting the main crop on deep soils with no line horizon, and almonds and olives on medium deep soils with a carbonate accumulation horizon. Oil crops, such as sunflower and flax, have grown successfully on these soils and they make up, with some vegetables, the remainder of the cropping pattern. In summary, 33% are occupied with alfalfa, 33% with vines and 33% with oil crops and vegetables.

9.4.7 The nutritional problem

It is known that calcareous soils with a high percentage of CaCO3 have a pH greater than 8 and may reach 8.6. Thus, deficiency symptoms of most plant nutrients and in particular of phosphorus are expected to appear on almost all crops. Up to the present, no proper technique has been found to ensure a continuous supply of this nutrient to the plant. The application of the practice adopted for the Delta soils, where medium amounts of phosphorus are applied to legumes, has not given satisfactory results on the calcareous soils. It is essential to adopt the concept of initial concentrated doses of phosphatic fertilizers. A heavy application, sufficient to bring the available phosphorus to a certain level, should be made in the beginning followed by subsequent annual applications to maintain that level. This means that not less than 150 units of P2O5 acre should be applied when the land is first put to cultivation (2 400 kg/ha of superphosphate).

I think that it is due to the incorrect programmes for phosphatic fertilization that crop yields are lower than expected. Wheat for example can attain a good vegetative growth but grains do not reach the proper size.

The micronutrients are all deficient and detailed studies are needed to ensure proper application using new techniques such as spraying.

Nitrogenous fertilization does not pose a problem. The reaction of lime with ammonia is known and Egyptian scientists have studied the nitrogen problem and have made specific recommendations.

9.5. Conclusion

In conclusion, I would say that these are some of the main problems of the reclamation and management of calcareous soils in Egypt. I would like to draw your attention to the problem of secondary salinization which, to a great extent, is related to profile characteristics and water seepage. The engineering design of irrigation canals should be considered carefully when planning irrigation networks to avoid water seepage especially from higher ditches to adjacent low lands. The problem of salinity in the presence of CaCO3, is worth further investigation.

I thank you for your attention.

10. Problems of Regional Interest and Suggested Research Programmes for Calcareous Soils

by

L.T. Kadry
Regional Soils Specialist

A. Aboukhaled
Regional Water Management Officer

A. Arar
Regional Land and Water
Development Officer
FAO Regional Office, Cairo, ARE

10.1. Introduction

The suggested research programmes should aim at providing results that would contribute to advances and practical application in reclamation, improvement and management of calcareous soils in the Region. To give this wide ranged subject-matter and its interrelationships its due of comprehensive coverage would require involvement in unnecessary extraneous detail. This paper, therefore, attempts at indicating a number of salient research topics and lines of work from which might be selected a future course of action in formulating a research programme of practical significance.

10.2. Research Problems and Priorities under the Subject of Reclamation, Improvement and Management of Calcareous Soils

A. Research Problems

(a) Classification of calcareous soils into groups of mapping unit associations and series and the correlation of soil behaviour with soil characteristics. Parameters such as depth of profile; CaCO3 content, its textural fraction form and distribution; amount of organic matter, soil texture, structural stability and parent material may be taken as criteria for classification;

(b) Methods of land preparation for irrigated farming (levelling, contour farming);

(c) Fertility build-up and inter-relationships with calcium carbonate, (green manuring, farm manures, legume cropping; application of fertilizers, types of fertilizers and methods of application; especially micro-nutrients);

(d) Tillage practices in relation to soil structure stability and soil erosion;

(e) Soil crusting especially the early stages of soil reclamation and development (water management, organic matter and synthetic compounds, heavy seeding, use of spikes etc.);

(f) Improvement and management of irrigation methods, frequencies and practices (soil moisture characteristics, available moisture range, light versus heavy irrigation, new irrigation methods);

(g) Secondary soil salinization under calcareous conditions (rate of upward water movement and salts under different soil, crop and climatic conditions); alternative systems for the reclamation, improvement and management of these soils;

(h) Selection of suitable crops, crop varieties and root stocks with lime tolerant qualities;

(i) Drainage requirement for the control of water table of soil salinity.

B. Priorities
(a) Soil fertility problems; application of phosphate and micro-nutrients; addition of organic matter;

(b) Soil and water management practices; tillage practices to minimize crusting problems; soil erosion by wind and water; irrigation methods and schedules;

(c) Selection of suitable crops, crop varieties and rootstocks of fruit trees with lime-tolerant characteristics.

10.3. Possible Lines of Activities and Research on Calcareous Soils

(1) Soil Survey

An attempt should be made to classify calcareous soils in terms of their relative capacity (or effect) to induce chlorosis in major field and horticultural crops and in relation to their relative inducement of adverse soil and crop physico-chemical and biochemical conditions.
(2) Soil Physics
- Improvement of soil structure;
- Amelioration of surface crust conditions;
- Range of optimum soil-water relations;
- Effect of the textural fraction of CaCO3, particles upon reducing chlorosis in crops,
(3) Soil Chemistry
The system CaCO3 - pH - HCO2 - CO3 - H2O has to be studied in terms of all possible permutations of these variants and their relationships under controlled environmental conditions.
(4) Soil Microbiology
- Legume inoculation for improving Nitrogen-fixation;
- Effect of organic manure;
- Action of the beneficial microflora upon lime - induced chlorosis.
(5) Soil Fertility and Plant Nutrition
- The N.P.K.: time of application, form and type of fertilizer, placement and rates of application;

- Phosphorus availability, PK interaction in calcareous soils; micro-nutrients, pH;

- Comparing tolerant with sensitive variety and strains of crops in relation to calcareous soils;

- Use of lyphillization (fast freezing) in identifying the metabolity of the lime-induced chlorosis condition of the growing crop or plant;

- Translocation of nutrients, antagonism between elements with special reference to Ca++ K+ etc. (Ref, A. Khatib);

- Minor element deficiencies; foliar application of nutrients, chelating agents to control chlorosis (application to dry farming versus irrigated conditions). (Ref. work of Dr. A. Mattar - Syrian Arab Republic).

- Physiologic and genetic facets of crop tolerance to lime - induced chlorosis, criteria of soil classification.

(6) Clay Mineralogy
- Effect of the clay mineral constituents upon the incidence of chlorosis in calcareous soils;
- Identification of the clay mineral fraction of calcareous soils;
- Varying the specific surface areas of CaCO3 particles in calcareous soils.
10.4. Proposed Approach for Attempting Solutions of Calcareous Soils Problems

To realize effective solutions to the field problems of calcareous soils, it is necessary that a concerted cooperative and regional approach be taken by the countries of the Near East along the following course of action!

(1) Delineation through soil survey of calcareous soil areas that are acutely afflicted with the problems of lime-induced chlorosis. This field study is to be combined with a detailed characterization of the soils of these areas.

(2) Establishment of representative Pilot Experiment Areas for the conduct of laboratory/greenhouse/field experimentation on: (i) multivariant single or double factor experiments; (ii) multivariant multifactor experiments. The subject-matter of this programme may be selected from the relevant facets of soil physics, soil chemistry, soil microbiology, soil fertility, plant nutrition and clay mineralogy. As an integral part of this approach, field experiments on the following factors are proposed: Cultural Practices, Crops and Cropping Patterns; Irrigation and Drainage Practices, Amendment and Fertilizer Applications.

(3) Establishment of Representative Pilot Development areas on land and water use of calcareous soils for which a cropping pattern of relevance to the local rural community be implemented. Account has to be taken in this respect to apply the pertinent reclamation, improvement and management practices for calcareous soils. Since these field operations have to be carried out on profitable agricultural production economic grounds, it is imperative to keep the input/output record of the major field operations. This information has to be duly analysed and interpreted in terms of the criteria for realizing economic profitability.

(4) Collection, review, analysis and dissemination of the literature on relevant problems of calcareous soils published in the countries where progress has been achieved in this line of action.

11. Progress Report on the Regional Applied Research Programme on Land and Water Use in the Near East

by

A. Aboukhaled
Regional Water Management Officer
FAO Regional Office, Cairo, ARE

11.1. A BRIEF REVIEW OF THE APPLIED RESEARCH PROGRAMME FOR THE HEAR EAST REGION

1.1. Introduction

The countries of the Region are realizing more and more the serious impact of problem soils and of poor water management upon their agricultural production economy and upon the social welfare of the rural population. Serious efforts and measures are being taken by these countries in collaboration with FAO to determine practical solutions for improving this situation. The rapport of the countries for the Regional Applied Research Programme for Efficient Use of Land and Water is a testimony to this trend.

The Regional Applied Research Programme has so far been handled, from the FAO side, as a small scale Technical-Assistance-type Project (TA). The current transition from the status of a small-scale TA-type project to the status of a large-scale Regional Project has been associated from both FAO and the Near East Regional Commission on Land and Water Use with a very active preparatory phase.

At present, the Regional Programme is at its preliminary implementation stage. The Commission recommended to the Governments, during its Third Session (December 1971) that they take necessary steps to implement their share of the Regional Applied Research Programme for 1972-73. It is hoped that the full-fledged larger-scale operations will be launched by January 1973 pending the approval of the Regional Project by UNDP.

1.2. Phases

The main landmarks during the preparatory phase of the Regional Applied Research Programme on Land and Water Use consisted of: three Near East Regional Seminars; an Ad Hoc Consultation; three Sessions of the Near East Regional Commission on Land and Water Use; a three-month consultant's mission; and several missions of FAO Land and Water Officers to the various countries in the region. The preparatory phase covered the following aspects:

(a) The establishment of the Regional Commission, as a Statutory Body of FAO, by the FAO Council during its 46th Session in 1966. One of the major objectives was to assess priorities for the elimination of factors limiting efficient land and water use in the Region.

(b) The Regional Seminar on Land and Water Use in the Near East, Beirut, September 1967 where Technical Problems of Hater Use in Agriculture and of Land Use Planning in the Near East were discussed.

(c) The First Session of the Regional Commission on Land and Mater Use in the Near East. Beirut, September 1967 which proposed the establishment of the National Land and Water Use Committees and defined their functions.

(d) The Ad Hoc Consultation to Review the UNDP/FAO Land and Water Use Projects in the Near East, Amman, May 1969. Fifteen possible subjects for a Regional Applied Research Programme were identified and the methodology to tackle them was outlined. The establishment of a Regional Applied Research Programme was proposed.

(e) The Second Session of the Regional Commission on Land and Water Use in the Near East, Cairo, September-October 1969. The Commission recommended to the Governments of all Member Nations of the Region and to the FAO Director-General to establish and initiate the implementation of the Regional Applied Research Programme. First priority was given to problems considered of most immediate concern to the Region, namely:

- Reclamation, improvement and management of:
(i) salt affected and waterlogged soils;
(ii) calcareous soils;
(iii) sandy soils; and
- Efficient use of irrigation water, taking into account crops, cropping patterns and the efficiency of irrigation methods.
(f) The 10th FAO Regional Conference for the Near East, Islamabad, September 1970, accorded high priority to the Regional Applied Research Programme on Land and Water Use.

(g) The collection of information on the applied research situation in Land and Water Use from Member Countries through FAO and UNDP Country Representatives and Experts on FAO/SF projects.

(h) The Regional Seminar on Methods of Amelioration of Saline and Waterlogged Soils, Baghdad, December 1970, A brief preliminary review on the situation of applied research in Land and Water in the Region was presented. The need for standardized methodology and date systematization was recognized by the specialized government agencies.

(i) The three-month Consultant's mission (December 1970-February 1971) to visit the countries in the Region and investigate the research situation in relation to the Regional Applied Research Programme. A plan of work was delineated by the Consultant (Rafiq) in collaboration with the FAO Land and Water Officers. The Consultant's report entitled "Regional Applied Research Programme - An Evaluation of the Present Situation and Proposals for Action" was distributed to Governments in the Region in August 1971.

An important finding reported was the following: Among the 67 institutions surveyed in 18 countries in the Region: (i) 38 are tackling problems related to salt affected and waterlogged soils; (ii) 36 are carrying out applied research on effective use of irrigation water; (iii) 23 are working on calcareous soils; and (iv) only 8 are engaged in reclamation, improvement and management of sandy soils.

(j) The Regional FAO/UNDP Seminar on Effective Use of Irrigation Water at the Farm Level, Damascus, December 1971, emphasized that correct determination of water requirements of irrigated crops is essential for project planning and operation. A common methodology was recommended to facilitate the comparison of results. Inter-disciplinary cooperation for land reclamation and land and water management was also emphasized since lack of adequate field drainage and inadequate water applications are the main causes of resalinization after reclamation. Background papers dealt with investigations on: (i) the existing salinity and sodicity classification limits under the Near East conditions; (ii) the optimum water table depth for drainage design on an economic basis; (iii) the hydraulic soils' characteristics for design of drainage systems; (iv) the crop water requirements; and (v) the sampling, analysing and mapping of salt affected soils. Within the context of the four priority lines of action of the Regional Applied Research Programme, the following objectives for the Regional programme were endorsed:

(1) To disseminate to countries of the Region information on the currently active applied research centres. This information covers the programme of work, names of research and technical workers, their fields of specialization and their research and technical accomplishments.

(2) To assist in determining uniform technical criteria and standards for field problem identification, methodologies of field survey and investigation and technical field development operations.

(3) To assist in establishing field experimental programmes and work plans for pilot project areas at the country, sub-regional and regional levels, The findings of these and other technical activities will be cumulated in a central soil data bank for analysis and retrieval.

(4) To assist in the review and development of the technical programme of work of the applied research centres in the countries of the Region.

(5) To assist in determining a system for cooperative and complementary coordinative working relationships between the applied research centres which work on problems of common interest in the countries of the Region.

(6) To assist in inducing a system for developing cooperative and coordinative relationships between the applied research workers and technicians who are attached to interrelated sectorial government services namely: applied research, education, extension and pilot project area operations.

(7) To assist in initiating and/or strengthening training centres for the technologic training of technicians at the country, sub-regional and regional levels.

(k) The Third Session of the Regional Commission on Land and Water Use in the Near East, Damascus, December 1971, advised starting on two lines of action for the Regional Applied Research Programme. The Commission agreed to give priorities to 3 experiments: (i) Reclamation of salt affected soils; (ii) Management of leached soils; and (iii) Crop water requirements. Guidelines and experimental layouts, prepared by FAO consultants or officers, were given for consideration by the Commission. The Commission indicated that time is needed for their study and evaluation on a regional basis; comments should be forwarded to the prospective authors who will report during the next regional seminar. On the other hand, the Commission recommended integrated type experiments taking into account the crop production factors. The Commission urged the Member Countries to submit their comments after testing the guide- lines for sampling, analysing and mapping of Bait affected soils. Finally, it supported and endorsed the draft request for a 5-year Regional Applied Research Project (1973-1977).

(l) The Guidelines and experimental layouts on (i) leaching of soluble salts; (ii) management of salt affected soils; and (iii) crop water requirements, including the variants and factors agreed upon by the Commission, were distributed in February 1972 to the countries in the Region, for remarks and comments.

(m) The three-man mission to Iraq, Syria, Jordan, Lebanon, Sudan and the Arab Republic of Egypt, 30 January-22 February 1972, clarified the purpose of the Regional Project, the Governments and UNDP Contributions.

(n) The Regional Project for Applied Research on Land and Water Use was endorsed by eleven countries in the Region. This five-year project aims at the establishment and support of a coordinated regional programme for applied research in four priority lines of action listed under (e) above. Its main role would consist in the standardization of the research methodology, initiation of a regional approach to the problems, coordination of the applied research activities, assistance in the exchange of information within the Region and education and training of technicians and field staff in irrigation, drainage and land reclamation.

(o) The recent missions to the countries by the Regional Land and Water (TA) Officers. The 3 guidelines were presented to the specialists and research workers for comments and eventual implementation of the experiments in 1972-73. Issues and factors affected by local conditions, such as crops, crop rotations, fertilizer levels and agricultural calendar for field operations were discussed and agreed upon in most cases. The seven participating countries (Egypt, Iraq, Iran, Jordan, Lebanon, Sudan1/, Syria) and two supporting (Cyprus and Kuwait) were visited in 1972. Detailed reports were written on their situation and progress (See References).

(p) A consensus was reached by the Eleventh Near East Regional Conference (Kuwait September 1972) on according first priority to the Regional Applied Research Programme for Land and Water Use in the Near East.

1/ Sudan only was not visited when this report was submitted.
11.2. PRESENT STATUS IN THE VARIOUS COUNTRIES OF THE REGION

2.1. Agreements Reached at the Third Session of the Regional Commission on Land and Water Use in the Near East

The situation of the applied research in the various countries in relation to the four lines of action of the Regional Project was briefly reviewed during the Baghdad Seminar (December 1970). A more detailed picture was presented in December 1971 (Damascus Seminar and Third Session of the Regional Commission).

During its Third Session, the Commission discussed the situation, needs and possibilities concerning the execution of three experiments (leaching of salt affected and waterlogged soils, management of reclaimed soils and crop water requirements). The outcome is summarized in the following Tables (1 and 2).

Table 1. Information on the Experimental Sites for Leaching and Management of Salt Affected Soils, Executing Organizations and Officer-in-Charge

Table 2. Information on the Experimental Sites for Effective Water Use at the Farm Level Executing Organizations and Officers-in-Charge

2.1.1 Design and preparation of experiments

Preparation of guidelines and designs toy FAO with the help of a statistician for the experiments on leaching and management of salt affected soils and water use efficiency were to toe ready toy the end of January 1972. The detailed design of experiments were to toe submitted directly to the National Committees and the persons responsible for the experiments.

Selection and preparation of sites for experiments toy the countries and execution of preparatory work were to take place from January to March.

All soil and water samples, and groundwater level measurements were to toe collected prior to sowing which was scheduled from March 1972 onwards.

2.1.2 Types of experiments

Three types of experiments were discussed for a regional approach:

(a) Leaching of virgin, saline soils

The following treatments were to toe included:

- Leaching methods: continuous versus intermittent
- Depths and spacings of drains: 3 depths and 3 spacings
- Time of leaching: summer versus winter
- One type of drain - if possible tiled, otherwise open.
(b) Management of reclaimed land

The following treatments were to toe included:

- Summer fallow versus non-fallow

- Ploughing during fallow versus non-ploughing

- Fertilizers and amendments, optimum level of fertilizers in the country for the crop versus non-fertilized

- Two water regimes

- Sub-soiling versus non-sub-soiling, in heavy saline or sodic soils as the case in Sudan and Egypt

- Crop rotation: the following rotation has been agreed upon: rice or cotton followed toy barley or berseem fallow or sorghum followed toy cotton, barley or berseem followed toy rice.

(c) Efficient water use at the farm level
- Irrigation at 4 tension or depletion levels: the normal established practice was to toe included as one treatment

- One crop in summer and one in winter, alfalfa is also recommended as a permanent crop. The experimental site should have deep water table whenever possible or tile drainage if needed

- Surface irrigation methods: basin or furrow

- Optimum management practices for the crop in the country should be followed.

2.2. Situation and/or Progress after the Third Session

After the Third Session of the Commission (Damascus 14-18 December 1971), the Regional Land and Hater Officers established contacts with the officers in charge of the Regional Applied Research Programme in the various countries of the Region, visited their Research Institutions, Experimental Stations and a number of FAO field projects.

The Regional Officers' Duty Trip Reports cover the details of the discussions and specifications on the methodology of executing the field experimental programmes as outlined in Tables 1 and 2 for each respective country. The following paragraphs cover the salient actions taken by governments and the important constraints and recommendations given by the Regional Officers to the countries concerned during the course of their duty trips.

2.2.1 Arab Republic of Egypt

1) Daring the course of the joint meeting on the new ARE agricultural policy held at the Ministry of Agriculture on 21-22 August 1972, in which participated the senior officials of the Ministry of Agriculture and Land Reclamation and the Regional Officers, His Excellency the Minister, Dr. M. Elgabaly, decided to commission two ARE research officers, one specialized in Soils and the other in Water Management who would be entrusted with the task of surveying and appraising the available ARE literature in their respective fields with particular reference to the four priority lines of action of the Regional Applied Research Programme.

2) The FAO Regional Office will recruit the services of a Regional Consultant for two months after December 1972 to survey, appraise and evaluate published and unpublished work of applied research on land and water use in Egypt and the Sudan with special emphasis on applied research in the fields of irrigation and reclamation, improvement and management of salt affected and waterlogged soils.

3) Details of the 1972/73 programme were thoroughly discussed during meetings with Drs. Shabassy, Mitkees and Barak and senior staff.

2.2.2 Iraq
1) Recommendation that Abu Ghraib Water Requirement Experimental Field becomes a major central site in the country for evapotranspiration and water optimization studies and that supporting work be carried out at Khales and El Mussayeb.

2) Emphasis to be given at El Mussayeb on the evaluation of irrigation method and improvement of water use efficiency under normal size fields.

3) Waterlogging is the main water management problem which is accentuating the spread of soil salinization throughout the entire irrigated Raifidain (Mesopotamian) Plain. It is therefore, crucial that the Government takes urgent measures to check seepage by adopting a policy coupled with an action programme for the lining of irrigation canal networks and the control of water table depth by proper drainage and the control and timing of field irrigation applications.

4) Iraq appointed Dr. Kawaz to activate the implementation of the water use experiment.

2.2.3 Jordan

The two consultant reports by Dr. Van den Berg (mission 25/2 to 6/3 1972) stressed the following:

1) There is a potential salinization of pumped groundwater by leached salts. A Hydrogeologic survey is necessary to evaluate this condition.

2) Land levelling coupled with leaching and control of water losses should be exercised, a sequential system of general field levelling construction and levelling of basins and borders; first irrigation (200 mm); re-levelling two weeks later; pre-planting irrigation and planting should be exercised. Intermittent leaching should be carried out in the highly salinized areas.

3) Gypsum or sulphur amendment application should be investigated for economic justification.

4) Sand application ameliorates cultural practices in heavy soils but not infiltration on ESP level.

5) Methods of irrigation coupled with economic use of water should be investigated. The following points were stressed by the Regional Officers duty trip reports:

- The criteria for sound soil/water/crop management have to be derived from integrated field experiments in representative soil mapping areas.

- For the rational development planning of the country's land and water resources, it is necessary to carry out standard soil survey and classification at an appropriate reconnaissance scale.

- Concurrently with standard soil survey and classification, the need is also pressing for collecting information on soil fertility survey and agro-climatologic mapping and zonation at the country level.

- In view of the hazard of waterlogging to which the East Ghor region is exposed, it is recommended to recruit a field drainage expert to investigate the project area's drainage requirements.

6) Water requirement experiments and evaluation of surface and sprinkler irrigation methods are advancing at the Quatrana Farm.
2.2.4 Lebanon
1) There is a pressing need to take immediate action in starting the operation of the precision weighing lysimeter for the Regional Applied Research Programme. The recruitment of an additional researcher for irrigation is essential.

2) Applied research on irrigated calcareous soils at the Lebaa Station should be strongly fostered since varying calcareous soil conditions exist in its vicinity.

3) Bibliographic references were classified and pertinent articles reviewed in the following fields by the Regional Water Management Officer:

- Lysimetry and Measured Potential Evapotranspiration
- Evapotranspiration (ET)Estimates (Formulae)
- Crop Water Use
- Soil Moisture Conditions Plant Growth and ET rates
- Irrigation Control and Guiding
- Irrigation Methods (Evaluation)
4) The advanced state of the applied research work on irrigation and water requirement of crops in Lebanon qualifies it to assume a leadership role in extending the field methodology of this line of the Applied Research action to the countries of the Region through eliciting standardised field application procedures and training of technical personnel. This objective can effectively be realised through the Regional Applied Research Programme for Land and Water Use.

5) The need is crucial to fill the presently vacant posts of soil physics (soil water relationships) and soil microbiology in the Tel Amara Agricultural Experiment Station.

2.2.5 Syrian Arab Republic
1) Standard soil survey of the entire Euphrates project area at the required scale of detail has to be completed.

2) The Regional Applied Research Programme can assist in coordinating, strengthening and, may be, centralizing all research work leading to the efficient use of irrigation water and the reclamation, improvement and management of salt affected, calcareous and gypsiferous soils. A full-time team leader or specialist in water use studies is needed. A close technical collaboration at the planning, implementation, supervision, control and analysis levels is essential at this stage between the subject-matter government offices and Universities.

3) Once the crop and animal systems for the pilot areas of the Euphrates Agricultural Development Project have been determined at the policy administration level, it is recommended that multi-variant test/demonstration field investigations be carried out to determine the outcome of the interactions linking the variants on soils - land preparation and cultural practices -cropping patterns - irrigation and drainage practices - water table conditions and control of soil salinization and fertilizer use. These test demonstrations have to be simplified such that selectivity be exercised in limiting the number of treatment variants to the minimum possible. They are to be carried out at three working levels namely:

(i) In Pilot Field Experimental Areas in association with field experimental layouts that conform with the statistical requisites.

(ii) At the Farmers' Fields in association with the extension service technicians.

(iii) At the Pilot Development Areas on a multi-disciplinary scale in conformity with the locally acceptable concepts of farm management cooperatives the agricultural produce of which is to be prepared for marketing.

4) Immediate implementation of the standardized "Crop Water Requirement Experiments" is recommended at the Billanah Experiment Station (GADEB), at the El Ghab Project (El Ghab Development Authority) and at Douma (Soils Directorate) with the best crop rotations and fertility levels convenient to each site. The lysimeters, meteorological stations or neutron probe available in some of these locations will serve as a starting point. The additional instrumentation and equipment required will be, to a large extent, provided by the Regional Applied Research Project subject to its approval by UNDP.

5) Collaboration with the Arab Arid Zone Centre is recommended.

2.2.6 Other Countries

A. Cyprus

Cyprus is so far a "supporting" and not a "participating" country in the Regional Applied Research Programme. However, it is actively involved in work on efficient control of irrigation applications, on use of low quality waters, and on improved irrigation methods in relation to the associated factors of crop production.

The Water Use Section of the Agricultural Research Institute could be strengthened to provide all the information and measured values on:

(i) Potential evapotranspiration in the major climatic zones and land use areas of the Island.

(ii) Net irrigation requirements for the major crops in each area and the recommended irrigation intervals to attain optimization per unit of water applications.

(iii) Gross irrigation requirements taking into account the efficiency of the irrigation method or of the field water application. This involves the comparison and evaluation of the various irrigation methods (sprinkler, basin, drip, border, furrow) and the field irrigation efficiency.

B. Iran

Both the Soils Institute and the Agricultural Engineering Department are interested in the Applied Research Programme.

(i) A higher intensity of land use in the rice growing area of Mazandaran Rasht has to be continued through utilizing the winter fallow period by an appropriate crop.

(ii) In the case of tea culture the outcome of the interaction between irrigation application and fertilizer use increased the yield of tea significantly. Further experimentation should be carried out with a view to determining the combination of irrigation and fertilizer levels which assures the highest economic return.

(iii) Citrus is being grown so far without irrigation (Guilan area). It is felt that irrigation would raise citrus yield. It is therefore recommended that irrigation combined with fertilizer use experiments on citrus be initiated.

(iv) The identification and analysis of the clay mineralogical constituents of the clay fractions in soils would contribute to improving the efficiency of fertilizer use - phosphorus in particular. The possibility of identifying institutions in the region willing to cooperate in carrying out clay mineralogic analyses would be investigated by the authors.

(v) Since the major sources of waterlogging and salinization in the Ahwaz region is the seepage from irrigation canals and misuse of irrigation water the current canal lining action programme being carried out by the Soils Institute should be encouraged and be further expanded. It is also urged to carry out regular waterlogging and soils salinization surveys in all the semi-arid and arid zones of the country in the form of supplementary monitoring activities to the soil survey, land classification and evaluation field operations.

(vi) It is commendable to note the initiative taken by the Soil Institute in planning the establishment of a pilot development area in the extension sector of the Rasht experiment station. This action will enable the introduction of land and water use production economic criteria to arrive at input/output ratio and economic feasibility assessment of the agricultural areas. This background data is essential for planning development in land and water use as well as in improving the criteria of the systems of land evaluation and land suitability classification. For the purpose of executing this line of action on a sound basis it is necessary to recruit the services of a farm management or an agricultural production economist.

(vii) Attention is brought to the importance of the recently published articles (see USA Journal of Irrigation and Drainage, Division of the Civil Engineering Proceedings, June, 1972), which covers both the aspect of Potential Evapotranspiration in relation to irrigation design, tolerances and to Soil/Plant/Water Relationships.

2.3. Comments on the Guidelines and Experimental Layouts

Special efforts were made by the Land and Water Regional Officers to collect as many comments as possible on the FAO Guidelines and Experimental Layouts. Viewpoints of specialists and researchers in the various countries are summarized below:

A. Comments on the Guidelines for Crop Water Requirement Experiments

For countries and conditions where salinity and shallow water table are not prevailing, the guidelines were, in general, well accepted. Important points raised and comments made are the following (refer to Guidelines) :

(i) Under the basic considerations, crop yield should be mentioned.
Answer: the suggested field experiments result actually in yield responses to differential irrigation treatments.
(ii) The sentence "ample but measured water" should be explained.
Answer: the amount of water to be applied is equivalent to the crop lysimeter value (no water stress) for the same period. The idea is to wet thoroughly the soil profile in order to allow good root development. Occasional neutron probe measurements are essential to assess the application efficiency and the actual water use under the given irrigation interval as well as the moisture extraction pattern of the crop under the given irrigation treatment.
(iii) Loss of water by deep percolation in the plots should be assessed.
Answer: whenever possible, this laborious and time-consuming assessment should be made. A neutron probe, a number of mercury tensiometers placed at various depths down to 2.50 m, a cropped plot and a bare soil plot are required. Cyprus is undertaking such measurements in collaboration with the IAEA. Results and comments are expected. Meanwhile, it is assumed that internal drainage is significantly reduced 2 to 3 days after irrigation. Correction or refinement of the results is always possible at a later stage.
(iv) The plot size seems too small.
Answer: the plot size suggested should exceed 25 m2 Actually, small basins of 25 to 50 m2 are most common in the Near East Region. Most countries favoured for crop water use studies sizes of either 50 or 100 m2. Larger sizes are suggested for application efficiency and water distribution uniformity studies under various surface irrigation methods (field level).
(v) More treatments outside the tensiometer range were requested.
Answer: water retention (pF) curves and irrigations at 2, 5 and 15 bars are suggested. The soil moisture tension corresponding to actual plant wilting observed early in the morning should be determined and is used, in the guidelines, for the irrigation timing of one treatment. At the end of the experiment, yields versus soil moisture tensions are given. The irrigation intervals along the growing season corresponding to the various tensions should be explicitly given for practical use. In addition to the neutron probe, certain countries asked to introduce the use of psychrometer to measure the soil water potential instead of the metric potential or water content.
(vi) The precautions essential for obtaining sound data from the lysimeters should be emphasized.
Answer: the writer prepared an outline on "Lysimetry and its Use for Crop Water Requirements". It was discussed at the Panel of Experts (Rome, 3-8 September 1972) and the final report will be distributed to countries participating in the Regional Applied Research Programme. For the first year, it is suggested to have two lysimeters under the same crop to assess deviations. Three to four year data are required for each crop.
(vii) Certain countries, especially Iraq, Iran and Syria are interested in watercrop (population)-fertilizer interactions and economical analysis for optimum crop water requirements under different fertilizer levels.
Answer: This could be done by changing the experimental design to split-split plot of factorial and increasing naturally the number of plots.
(viii) Crops, crop rotations, fertilizer amounts and other treatments affected by local conditions (planting date and harvest ...) should not and/or could not be necessarily the same in all countries.
Answer: The Guidelines stress the standardization in methodology and systematization of data and results and provide sufficient flexibility for factors affected by local conditions.
(ix) In addition to the crop water requirement experiments, Cyprus, Egypt, Iran and other countries are interested in the use of low quality water on non-saline, non-alkali soils with no shallow water table.

(x) The evaluation of the efficiency of the various irrigation methods at the field level should go parallel to the crop water requirement experiments.

B. Comments on the Guidelines and Experimental Layouts for Reclamation and Management of Salt Affected Soils
(i) A split-split design was agreed upon instead of the randomized block design for the experiment on management of salt affected soils.

(ii) It was suggested (Iraq) to conduct the summer fallow versus non-fallow treatments under various groundwater table depths, at least two: one situated within the critical range for resalinization and one below this depth.

(iii) Crops, crop rotations, fertilizer levels and other factors affected by local conditions should not be rigidly imposed on all countries in the Region; selection of these variants has to be dictated by local conditions and needs.

(iv) The treatment with no fertilizer was requested to be replaced (Iraq, Egypt, Syria, Iran). Thus two fertilizer levels would be considered. The levels should be specified for each case based on local conditions, soil analysis and previous experience and results.

(v) The figure of 20% leaching requirement to be applied was argued in certain cases. On the other hand, suggestion was made (Syria, Iran) to include a treatment where the leaching requirement is given in one single application versus the fractionation treatment with 20% each time.

(vi) The overlap between leaching requirement and irrigation efficiency was often debated.

(vii) The soil sampling sequence must be unified for both experiments as follows: 0-15, 15-30, 30-60, 60-90, 90-120 and 120-150 cms.

(viii) The sub-soiling spacing (1 or 2 m) was agreed in relation to soil texture and structure.

(ix) The number, frequency and extent of soil and water analysis and observations are considered excessive in general. It was requested to reduce them and list the essential ones,

(x) The two depths of drainage were often questioned.

It was felt that the Guidelines and Experimental Layouts provided an excellent framework for standardization and were well accepted only when tailored to the specific needs of each country, (choice of the crops, crop rotation, fertilizer levels and priorities in the variables and treatments).

2.4. Follow-up Action on the Guidelines and Experimental Layouts

A. Convergence of Efforts in Crop Water Requirement Studies

Improvement of the present guidelines must be a continuous process. The writer - being a member of the Panel of Experts on Crop Water Requirements which pools efforts of Senior Consultants from USA, France, Holland, Lebanon and India - attempts to incorporate the recommendations of this Consultative Group, whenever applicable, to the Region. The first meeting was held at Tel Amara, Lebanon (May, 10-15, 1971) and the second in Rome (3-8 September 1972).

The main items discussed in the Rome meeting were:

(i) The development of a consolidated approach in determining crop water requirements from formulae using potential evapotranspiration (grass) as a standard reference.

(ii) Preparation of a guide on agroclimatological instruments and observation practices for use in FAO projects.

(iii) Preparation of a field manual on measuring and evaluating hydro-physical properties of soils.

(iv) Preparation of a study on the use of lysimeters in crop water requirement studies.

(v) Up-dating of the FAO publication entitled "Applied Irrigation Research".

(vi) Preparation of a comparative study on concepts and methods used in determining the effectiveness of rainfall.

(vii) Design of a system for storage and retrieval of crop water requirement information.

On the other hand, the International Commission on Irrigation and Drainage (ICID) has established a committee to study the use of lysimeters in consumptive use determination.

Finally, a U.S.A. team (M.V. Jensen and collaborators) started an important work on the same subject.

This concentration of scientific efforts on the crop water requirement at the international level is an excellent backing for this line of action of the Regional Applied Research Programme.

B. Recommendation No. 12 - Third Session of the N.E. Land and Hater Use Commission

During its Third Session, the Regional Commission recommended FAO to take the necessary action to establish a bibliography on previous and current research results and publications dealing with land and water use, giving priorities to those undertaken by the Near East Applied Research Programme.

At the country level, the National Committee on Land and Water Use should be more active and assist in providing a complete, true and analysed picture of the land and water research situation. This is particularly essential with respect to Egypt and Sudan due to the large number of institutions and researchers in land and water use. The Regional Office is taking action along this line in collaboration with the Ministry of Agriculture in Egypt.

C. Additional Information

Additional guidelines and a new experimental layout are necessary if salinity, water table, water quality, fertilizer, and water depletion interactions are to be studied in one integrated experiment.

11.3. SUMMARY AND CONCLUSIONS

(1) The Near East Applied Research Programme for Efficient Land and Water Use has been so far handled as a small Technical-Assistance-type project. The switch from small-scale TA-type to a large-scale Regional Project has required from the FAO side a very active preparatory phase in collaboration with the Near East Regional Commission on Land and Water Use.

(2) A more active participation in the 1972/73 Programme of the National Committees of the various countries of the Region is badly needed. It is hoped that full-fledged larger scale regional operation on reclamation and management of (i) salt affected waterlogged soils; (ii) calcareous soils; (iii) sandy soils; and (iv) efficient use of irrigation water - will be launched in January 1973, pending final approval of the Regional Project by UNDP.

(3) The modest start for 1972/73 advised by the FAO Secretariat during the Damascus Seminar (December 1971) was agreed upon by the Regional Commission. Guidelines and experimental layouts, Reclamation and Management of Salt Affected Soils, and Crop Water Requirement Experiments were issued and discussed. It was indicated that time is needed for their study and evaluation on a regional basis.

(4) Comments and viewpoints of specialists and researchers on the Guidelines and Experimental Layouts in the various countries were requested by the Regional Officers. Responses are given and discussed in this paper. While certain suggestions could easily be integrated in the proposed guidelines and experimental layouts, others would require further elaboration or even new experimental designs. This applies, in particular, to the request of the Arab Republic of Egypt for a compound experiment for interactions of fertilizer levels, salinity levels, water table depths and irrigation regimes. Iraq and Syria could benefit from the additional experimental layouts. Experiments for the use of low quality and brackish water were also requested (Cyprus). Results for immediate use in ongoing land and water development projects were strongly requested by Syrian and other Government officials. The need for improved irrigation methods and good training and extension was expressed to make full use of the crop water experiment data.

(5) At present, it may be considered that Crop Water Requirement experiments, according to or in line with the Guidelines, are fully operating in Lebanon, well implemented in Jordan, initiated in Cyprus, Iraq, Iran and Syria. The initiation was mainly within operating FAO projects.

(6) Management experiment implemented already in Iran. Steps towards the implementation of the reclamation of salt affected soils and the management of leached soils are being taken in Egypt, Iraq, Iran, Jordan and Syria. The experimental sites were selected and land preparation was proceeding during the FAO Officers' visit. Lebanon and Cyprus are not interested in the problems of salt affected soils.

(7) The establishment of a Bibliography on previous and current research results and publications dealing with the four lines of action of the Applied Research Programme is required. Bibliographical research was initiated for crop irrigation requirements.

(8) The roles of the Regional Commission and National Committees on Land and Water Use are essential for the implementation and success of the Regional Applied Research Programme. It is understood that the actual field implementation is the responsibility of the participating countries.

REFERENCES

Abbas M.H., Arar, A. and Kadry, L.T.- 1972, Duty Trip Report of Mission on Applied Research Programme for Land and Water Use in the Near East Region.

Aboukhaled A. 1972a, Guidelines for Crop Water Requirements - FAO, Mimeograph, FAO, RNEA, Cairo - 8 pages plus Annex.

Aboukhaled A. 1972b, Summary Report on Duty Trip to FAO Headquarters and Lebanon, 16 pages (11 pages of bibliography), FAO, RNEA, Cairo.

Aboukhaled A. 1972c, Outline on Lysimetry and its Use for Water Requirement Studies; Panel of Experts on Crop Water Requirements, 7 pages and Annex -FAO, RNEA, Cairo.

Aboukhaled A. 1972d, Action-Oriented Programme for Crop Water Requirements Studies at Quatrana Experimental Farm. Duty Trip Report to FAO Project Jordan 25, 15 pages.

Aboukhaled A. and Kadry, L.T,- 1972a, On the Implementation of the Applied Research Programme for Efficient Use of Land and Water Use in Syria. Duty Trip Report, 25 pages plus Appendices. FAO, RNEA, Cairo.

Aboukhaled A. and Kadry, L.T.- 1972b, Report on Duty Trip to Cyprus. FAO, RNEA, Cairo.

Dieleman P. and Massoud, F.L- 1972, Guidelines for Experiments for Leaching of Soluble Salts, 4 pages plus an experimental layout.

El Gabaly M.N. 1971, Guidelines for Sampling, Analyzing and Mapping of Salt Affected Soils. FAO Paper AGL:LWU/7/4.

Kadry, L.T. 1972, Duty Trip Report on Sudan, October 10-24, 1971. 16 pages plus Appendices. FAO, RNEA, Cairo.

Kadry, L.T. and Aboukhaled, A.- 1972a, On the Implementation of the Applied Research for Efficient Use of Land and Water in Iraq. Duty Trip Report, 23 pages plus Appendices. FAO, RNEA, Cairo.

Kadry, L.T. and Aboukhaled, A.- 1972b, On the Implementation of the Applied Research Programme for Efficient Use of Land and Water in Jordan, Duty Trip Report, 23 pages. FAO, RNEA, Cairo.

Kadry, L.T. and Aboukhaled, A.- 1972c, On the Implementation of the Applied Research Programme for Efficient Use of Land and Water in Lebanon, 16 pages. FAO, RNEA, Cairo.

Massoud, P.I. 1972, Guidelines for Experiments on Management of Salt Affected Soils, 5 pages plus an experimental layout.

Rafiq Mohamed 1971, Report (AGL:MISC/71/11) on the Land and Water Use Regional Applied Research Programme for the Near East. An Evaluation of the Present Situation and Proposals for Action, 75 pages.

Van den Berg, C. 1972, Report of a Mission to FAO Project Jordan 25 from 25 February to 6 March, 13 pages.

FAO Reports on the Sessions of the Regional Commission for Land and Water Use in the Near East:

First Session, held in Beirut, Lebanon, 28-30 September 1967, 37 pages.

Second Session, held in Cairo, ARE, 28 September - 2 October, 1969, 76 pages.

Third Session, held in Damascus, Syria, 14-18 December, 1971. Report AGL:LWU/REP/72, Rome, 61 pages.

FAO Report No. TA 2425 - 1968, Seminar on Land and Water Use in the Near East, held in Beirut, Lebanon, 25-30 September 1967. Vol. II - Technical Documents, 155 pages.

FAO Report 1969, LA:SP:TCNE/69/REP on the Ad Hoc Consultation to Review UNDP/FAO Land and Water Use Projects in the Near East, held in Amman, Jordan, 12-17 May, 1969, 73 pages.

FAO Report 1971, Regional Seminar on Methods of Amelioration of Saline and Waterlogged Soils, held in Baghdad, Iraq, 5-14 December, 1970. Irrigation and Drainage Paper No. 7, Rome, 254 pages.

FAO Report 1971, AGL:LWU/REP on Ad Hoc Consultation on Crop Water Requirements, Tel Amara, Agricultural Research Institute, Lebanon, 10-15 Hay, 1971, 16 pages.

FAO Report 1972, AGL:SF/IRA 18 of the Soil Institute and Associated Pilot Development Project, Iran. Water Management and Soil Reclamation Tech. Report 3, Rome, 61 pages.

FAO 1971, Draft Request for a Regional UNDP Project - Near East Applied Research Programme for Land and Hater Use, 18 pages plus Appendices.


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