3.9 Rehabilitation of saline environments
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Principal Research Officer,
Division of Resource Management, Western Australian
Department of Agriculture
Salt-affected environments may be transformed from sources of erosion and desertification to areas producing valuable forage, fuel and other products. As a result, good agricultural land may be freed for the production of essential but non-salt-tolerant crops.
Engineering solutions, the mainstay of reclamation programmes in the past, are unsatisfactory for many areas because of water shortages, high costs, material shortages (e.g. fuel) and technical problems (e.g. water quality, impermeable soil, lack of disposal areas). A possible alternative is to grow plants possessing sufficient salt or alkali tolerance to withstand the conditions without reclamation. Increasing attention is being focussed on the use of highly salt-tolerant plants for growing on salt-affected soils (Barrett-Lennard et al, 1985) or for irrigating with highly saline water (O'Leary et al, 1984).
Recent estimates (FAO, 1982) show that 44 countries in Africa and South Asia are critically short of agricultural land to support their populations. In addition, fuelwood supplies are being rapidly and severely depleted by over-utilization of vegetation (FAO, 1981). Countries in Africa and South Asia contain 183 x 10 ha of salt-affected land (Dudal & Purnell, 1985), 91 x 10 ha of which is classed as solonchak soils with electrical conductivity of the saturation extract (ECe) levels of 1500 mS m-1 within the upper 0.75 to 1.25 m of soil. These soils are suited to the growing of halophytic plants but not normal glycophytic crop plants (Malcolm, 1985a). A further 11 countries in Central America are critically short of land for agriculture but there are only 2 x 10 ha of salt-affected land in this region.
Salt-affected soils are usually highly erosive, due to high exchangeable sodium levels; they are frequently bare due to over-utilization, and they generate salt and/or soil laden winds or run-off to streams or adjacent land. The poor vegetative cover on many salt-affected areas is ineffective in using saline groundwater; as a consequence groundwater levels are unnecessarily high and may contribute to streams or underground water reserves. Revegetation of saline areas controls wind and water erosion, assists in using excess groundwater, provides food and cover for domestic animals or wildlife and/or provides fuelwood and improves aesthetics.
Saline and alkali conditions limit the range of plants which may be grown on a site (Richards, 1954) and may restrict the yield even from highly tolerant plants (Greenway and Munns, 1980). Conditions for establishment of plants on saline soils are highly unfavourable (Malcolm, 1985b). As a consequence, salt-affected soils have been omitted from many revegetation programmes leaving extensive areas idle and unproductive. The purpose of this paper is to examine the potential for rehabilitating saline environments, to assess the constraints and to recommend programmes for future action.
2. SALT-AFFECTED SOILS
2.1 Distribution and extent
It has been estimated that 7% of the world's land area (0.92 x 109 ha) is salt-affected, 3% (0.40 x 10 ha) being dominantly saline or sodic. The regional distribution of this land is given by Dudal and Purnell (1985).
Estimates of the areas of salt-affected land in seventeen countries and the Sudano-Sahelian region are given in Table 1. Maps and compilations are available for a few countries (e.g. Australia, India, Pakistan). In some countries (Egypt, Sudan) the areas of salt-affected land are known only for irrigated regions but other areas of salinity are known to occur. Extensive areas of salinity are known to occur in countries such as Tunisia but no estimate of the area affected is available.
Salt-affected soils are classified on the basis of salinity and/or alkalinity values and profile characteristics (e.g., columnar structure in the B horizon, Szabolcs, 1974).
For the Soil Map of the World (FAO/Unesco, 1971-1981) the following limits were established for mapping:
|Solonchak||ECe||(electrical conductivity of the saturation extract) 1500 mS m within upper 0.75 - 1.25 m.|
|Saline phase||ECe||4 mS m-1 within upper 1 m.|
|Solonetz||ESP||(exchangeable sodium percentage) 15 within upper 0.4 m.|
|Sodic phase||ESP||6 within upper 1 m.|
The limit values for EC and ESP have different impacts in different parts of the world due to climatic plant and soil factors (Dudal and Purnell, 1985; Szabolcs, 1974). Other criteria such as SAR (sodium absorption ratio) may be preferred to ESP (Soil Science Society of America, 1971) and factors such as waterlogging may greatly modify the significance of salinity data (Barrett-Lennard, 1985). Therefore, flexibility in the application of limit values has been recommended (Szabolcs, 1974). Dudal and Purnell (1985) identify a need for data on the critical limits for salinity and sodicity under specified conditions with particular species.
Limit values for forestry on salt-affected sites are poorly defined. At a "Workshop on Land Evaluation for Forestry" (Laban, 1980) sites were considered suitable for forestry if they were "not susceptible to salinization" (Bennema et al, 1980). Killian (1980) concluded that a single standardized world classification system for forestry sites was probably unrealistic. He recommended the use of standardised terminology and ample practical interpretation of the terminology used.
A system of land evaluation for rainfed agriculture (FAO, 1983) which adopts specified but flexible limit values for factors such as salinity, waterlogging (oxygen availability) and soil nutrient status may also be useful for forestry. Its adoption would require definition of the limit values that apply to particular species and environments. A salinity level giving 90% yield potential for a species is used to separate highly and moderately suitable sites. Marginally suitable and unsuitable sites are differentiated at the 'no yield' salinity value. The salinity boundary between moderately and marginally suitable sites is determined by economic and social factors.
2.3 Land evaluation for halophyte planting
Information from countries such as India and Australia indicates that the salt-affected land is divisible into several major types (see Table l) representing highly divergent ecological conditions.
Dudal and Purnell (1985) have distinguished five main groups of salt affected land, and sub-divided them according to three climatic zones. A further sub-division is given in Table 2 using climatic types shown in the Times Atlas of the World (1973), with an additional division of deserts into hot and cold.
Salt-affected coastal areas occur in most climatic zones but examples of endoreic (closed) basins were found only for Mediterranean, dry steppe and hot desert zones. The greatest concentration of examples in Table 2 is in the humid sub-tropical, Mediterranean and dry climates.
Within any one of these subdivisions the distribution of plants which grow on the salt-affected soils is governed by plant tolerance to factors such as inundation, depth to groundwater, soil type, rainfall and salinity (Novikoff, 1961; Kassas and Zahran, 1967; Ungar, 1972; Jefferies et al, 1979; Malcolm, 1983a; Sankary, 1985).
There is a need for a system of site classification which takes account of the ecological requirements of species.
Halophytes suffer a 50% reduction in growth at NaCl concentrations ranging up to 630 mm in aerated solution culture, compared to a maximum of 130 mm for the most salt-tolerant glycophytes (Greenway & Munns, 1980). These values correspond approximately to EC values of 5800 and 1300 mS m-1 respectively on field sites (Malcolm, 1985a,. The values may be compared with reported salinity levels in the field beneath communities of halophytic plants (Table 3). The lowest conductivities (in Table 3) are in most cases above the 50% growth reduction level for the most tolerant halophytes (5800 mS m-1). These high conductivities compare with those in soils where production of cereal crops failed due to salinity in Canada and Texas (Luken, 1962; Carter and Wiegand, 1965).
The distribution of halophytic species on salt-affected sites is zoned in response to minor differences in topography. Clarke and Hannon (1970) found that in tidal marshes elevation differences were associated with differences in inundation causing different levels of salinity and waterlogging. Halophytes on the site were zoned in accordance with their tolerance to salinity and waterlogging. The salinity and hydrology of sites have also been identified as the main factors influencing species distribution on inland salt-affected areas (Novikoff, 1961; Ungar, 1965; Sankary, 1985). More research is required to define the levels of salinity or waterlogging tolerance of particular species and how to characterize a field site in terms that relate to the tolerance levels defined.
Sites may be described on the basis of criteria necessary for growth or survival. A rare waterlogging event may kill species which have grown successfully on a site for many years. Alternatively some species may survive on a site without making significant growth.
Recommendations for characterizing salt-affected sites were made by the Research for Development Seminar on 'Forage and fuel production on salt affected wasteland' (1985) and are reproduced in Table 4. This system could provide the basis for a data bank on salt affected sites around the world. It would be complemented by information on species adaptation to the sites.
3. PLANTS FOR SALT-AFFECTED SITES
Rehabilitation of a saline environment depends on successful establishment of vegetative cover. Depending on site conditions, grasses shrubs and trees may be adapted. On severe sites it may be necessary to use pioneer species to ameliorate the site sufficiently for other more desirable plants to become established.
To choose suitable species cognizance must be taken of the adaptation of the plant to environmental parameters such as climate, salinity and site hydrology. In Table 5 species are classified according to the climatic zone and salt-affected land type on which they are reported to grow. The table is incomplete but illustrates a classification system which could be readily computerized to provide a list of species to test in a particular area. Further segregation of climatic types is possible (e.g. the dry steppe climates may have a dry summer or dry winter) and no indication is given of frost susceptibility. The salt-affected land types also require clearer definition.
The most important differences in salt-affected soils at any one site relate to site water relations. For coastal sites depth and frequency of tidal inundation or depth to the watertable are major factors affecting species distribution (Clarke & Hannon, 1970). In endoreic basin, seeps and areas with high water tables species zonation relates to the depth of watertable or susceptibility to inundation or surface waterlogging Novikoff, 1961; Sankary, 1985) as well as to salinity (Ungar, 1965). In Western Australia in a Mediterranean climate research has identified a range of plants suited to salt-affected areas with different characteristics. Species choice is facilitated for the farmer by relating it to rainfall and site descriptions (See Table 6).
Selection of species for salt-affected soils in Syria has been discussed by Sankary (1985) and the selection of wood producing species is dealt with by Midgley et al (1985). In most countries little work has been done to determine which species are adapted to the salt-affected areas. Limited observations indicate that salt tolerant plants may be grown outside their original habitats (Stalter and Batson, 1969) or in very different climates. For example, Atriplex undulate (from central western Argentina) grows well in a Mediterranean climate in south western Australia and on the Persian Gulf in Saudi Arabia; A. amnicola from north western Australia grows well in south western Australia and on the Persian Gulf; A. canescens from the south western United States of America grows well on the Persian Gulf but poorly in south western Australia (H.Z. Hyder personal communication, 1982). It has been observed that species unaccustomed to frost are winterkilled in colder climates (Sankary, 1985); There is an urgent need for a coordinated programme to exchange seeds, conduct adaptation tests, describe site conditions and develop a data bank on species adaptation to saline environments.
Suitability of plants depends on:
To screen for such a wide variety of criteria involves several steps. Firstly the plants must be capable of growing and reproducing under conditions representative of the problem area. Currently in Western Australia halophytic shrubs are being screened by planting single plant replicates as nursery raised plants on a 4 x 4 m grid. Blocks of 20 replications are situated on a range of sites to represent the conditions for which species are sought (B.H. Ward, personal communication, 1985). me shrubs are being screened for germination and establishment ability in a separate programme. A small number of selections is included in grazing experiments (Clarke, 1982).
An aspect of adaptation which has received little attention is the ability to establish. Improvements in establishment from direct seeding have recently been obtained by selecting species or strains of Atriplex amnicola which volunteer readily in the field (H.V. Runciman, personal communication, 1985).
4. REHABILITATION METHODS
For successfuly rehabilitation of saline environments it is necessary to select well adapted species, protect the area from utilization during establishment, use an appropriate establishment method and provide sound management of the new resource.
Establishment is often successful if nursery raised plants are placed in the field (McKell, 1985). If significant progress is to be made in rehabilitating the vast areas of degraded saline environment in the world it is essential to develop successful direct seeding techniques. Numerous factors affect the establishment of species on saline sites, (Malcolm, 1972 and 1985b). Successful establishment from sowing seed into saline soil depends on designing species and site specific methods. Strategies for improving establishment may include seed treatments (washing, threshing), seedbed modification to optimize water use and salt leaching (furrows, banks), mulches to modify soil temperature or conserve water (sprayed coatings, vermiculite, brush), and precise seed placement to take advantage of the foregoing (niches, spot placements). Seeding systems have been designed to combine some of these strategies (Frost & Hamilton, 1965; Herbel, 1971). The niche seeding technique (Malcolm and Allen, 1981) was designed specifically for sowing salt-tolerant forage shrub seeds into salt-affected sites in south western Australia. m e recommended method is as follows:
Problems associated with highly saline or waterlogged sites, and weed and insect control are the subject of further research but the method is now in use on a farm scale.
5. GRAZING HALOPHYTIC SHRUBS
Most information concerning the use of halophytic shrubs for grazing is from studies on natural stands rather than planted areas. About 20 million hectares of salt desert shrub range in western U.S.A. has been utilized since the 1880s, (Hutchings, 1965). Unrestricted grazing until 1930 destroyed or injured useful species and encouraged invasion by undesirable species. Reducing sheep and cattle numbers, spreading grazing more evenly and subdivision by fencing are management strategies which have reversed the changes. Initially the management change brings an improvement in the growth of established bushes which is followed by establishment of new plants. Recovery is slowest where greatest damage has been inflicted.
Detailed investigations of the effect of grazing intensity on salt desert vegetation indicate that removal of 75% of the available material on a species is too severe in any season (Cook, 1971). Removal of 50% in winter allows retention of vigour but removal should be limited to 25% in late spring and summer. Removing more material from bushes gives a sample higher in ash and lignin and lower in protein, cellulose, energy and phosphorus.
Effects of grazing by sheep and cattle have also been studied in Australia on rangelands including Atriplex and Maireana species. Over a century of grazing has caused much denudation (Trumble and Woodroffe, 1954). Damage is severe close to water supply points, but plants which are moderately grazed appear healthier than ungrazed bushes furthest from the water (Osborne et al., 1932). Careful analysis of the effects of sheep on a stand of A. vesicaria showed that the distribution patterns of the bushes were largely determined by trampling of seedlings and selective grazing of mature plants (Williams et al., 1978). Comparison of the effects of sheep and cattle grazing a mixed stand of A. vesicaria and perennial grass Danthonia caespitosa) indicates that cattle are less selective, with sheep grazing a higher proportion of grass and obtaining a diet higher in digestibility and nitrogen (Graetz and Wilson, 1980).
When alternative feeds such as annual grasses or herbs or perennial grasses are available, sheep have been found to ignore A. vesicaria and Maireana aphylla (Leigh and Mulham, 1966 a and b) and A. numularia (Wilson, 1966a). The shrubs are thereby conserved for stress periods. However, sheep fed A. vesicaria and A. nummularia exclusively, in pens, or in paddock plots, with fresh water available, have been found to make small gains in weight (Wilson, 1966a) an indication that the bushes are of value. Intake of A. nummularia was believed to be limited due to low palatability, a characteristic observed to be highly variable in this species (Jacobs and Smith, 1977).
Grazing experiments on stands of bushes planted as seedlings have been conducted in South Africa (Marais and Bonsma, 1941; Roux and de Kock, 1971; and Jacobs and Smith, 1977) and in Western Australia (Clarke, 1982). The results summarised in Table 7 show grazing capacities ranging from 1.7 to 8.1 dry sheep equivalents per hectare per annum. In each case the grazing capacity was determined during a short term intensive grazing akin to using the forage as a feed reserve. The economic significance of reserves of forage shrubs depends on the animal husbandry system in a particular region. For cereal and sheep farmers in Western Australia it has been shown that the grazing yields obtained by Clarke (1982), are highly profitable (Masson, 1982) if establishment, fencing and stock water supply costs are of the order of US$ 140 per ha.
There is evidence of a decline in yield from some species of planted shrubs after the first year (Clarke, 1982), but A. amnicola has maintained a high yield for five years, (C.V. Malcolm unpublished data).
Halophytic shrubs contain high levels of soluble salts in their foliage. Sheep ingesting these feeds excrete high levels of sodium (Wilson 1966b) and may develop diarrhoea (Sthälin and Bommer, 1958) a condition which is avoided by providing alternative low-salt feed. It is important to supply good quality drinking water with forages containing high levels of soluble salts, otherwise forage intake may be drastically reduced (Wilson, 1966b).
6. CASE STUDIES
During the Research for Development Seminar on "Forage and fuel production from salt-affected wasteland" (1985) held in May 1984, reports were received from 20 countries concerning their salt-affected areas and the work that needed doing. Four of these reports will be examined as case studies representing different regions.
6.1 Ethiopia (Sissay, 1985)
Recent estimates (Ministry of Agriculture of Socialist Ethiopia 1983) indicate that salt-affected flats have increased from 6% to 16% of the total land area of Ethiopia in recent years. At the same time forest has been reduced from 34% to 5% and woodland from 20% to 8%. About 9% of the population lives in the areas affected by salinity.
Ethiopia has the largest population of livestock in Africa, 25% of the livestock subsisting on natural vegetation in pastoral arid lowland. As wood is the most important source of fuel in Ethiopia there is enormous pressure on the natural vegetation from browsing and fuel gathering.
The vegetation on salt-affected areas is used by herds owned by nomadic pastoralists as well as by livestock from nearby settled farmers or migratory pastoralists from higher altitudes. Unrestricted use of the vegetation has resulted in deterioration and soil erosion.
There- is an urgent need to manage the existing vegetation for improved production and for research on species and methods for revegetating degraded areas.
6.2 Iraq (Abdul-Halim, 1985)
Iraq comprises 0.44 x 10 6 km² of which about 20% is salt-affected and/or waterlogged. Despite major land reclamation measures a vast area will remain affected for socio-economic reasons. There is intense pressure on the land due to population growth and rising living standards.
Vegetation on salt-affected land is cut for fuel and grazed by camels, sheep and goats. Intense exploitation has reached a highly destructive phase leading to denudation and severe soil erosion (Thalen, 1979). Programmes on the testing of salt tolerant shrubs for revegetating saline areas has commenced (Abdul - Halim et al, 1984; B.R. Rashid, personal communication, 1982). Sites affected by salt and/or waterlogging have been planted to A. lentiformis, A. nummularia, A. halimus, A. undulate, A. semibaccata, A. canescens, A. paludosa, A. amnicola, Salsola rigida and Maireana brevifolia with promising results. Experiments on the use of the niche seeding technique (Malcolm & Allen, 1981) have commenced.
6.3 Pakistan (Sandhu and Qureshi, 1985)
Salt-affected soils in Pakistan occur primarily in the Indus Plain and occupy 5.7 x 10 6 ha. (Rafique, 1975). Large scale drainage and irrigation schemes have been instituted in some areas but are expensive in terms of money, energy and water. A cheaper approach is to grow plants such as Leptochloa fusca which gives an economic return when planted on waterlogged, heavily saline, sodic soils (Sandhu et al, 1981). Work is proceeding in Pakistan to find plants which may be grown on drier salt-affected areas and will be available in winter when L. fusca is not growing. Trees and halophytic shrubs are included in the tests which include research on the growth of salt-tolerant plants using saline groundwater (1000 - 1500 mS m-1 electrical conductivity) for irrigation.
6.4 Western Australia
Farmers in south western Australia have lost about 0.3 x 10 6 ha of good cropland to salt encroachment. Prospects for returning all of the land to crop production using drainage and other measures are poor due to technical and economic constraints.
The plants in Table 6 have been selected during a long term testing programme for producing forage for sheep from land which will not produce cereal crops due to salinity. Establishment techniques have been developed and are detailed in extension literature for farmers (Negus, 1980, 1982; Malcolm, 1983b). Puccinellia ciliate, a grass from Turkey, is now widely grown by farmers in southern Australia. The sowing of shrub pastures using the niche seeding technique (Malcolm & Allen, 1981) is being developed commercially. Economic studies (Masson, 1982) have shown that if forage of sufficient quality is produced, the growing of Atriplex spp on salinized cereal land is highly profitable.
When saline land is adjacent to a source of seeds of desirable salt-tolerant forage species such as Mairena brevifolia, it is possible to create extensive shrub stands by management. Stock are excluded, bare areas cultivated and the species spreads rapidly. Within a few years it is possible to graze the area regularly in autumn.
7. GAPS IN KNOWLEDGE
For many countries there are estimates of the total area of salt-affected land and in some cases there is a sub-division into types. There is an urgent need to assess the capability of salt-affected land to distinguish between areas for which there are imminent prospects of being returned to production with non-halophytic crops and those that are likely to remain salt-affected. The latter grouping should be characterised in terms dictated by the growth requirements of relevant salt-tolerant plants. These growth requirements, which have still to be defined for many plants, include salt and waterlogging tolerance, climatic limitations (including frost), and tolerance to factors such as gypsum, lime or boron. The criteria should be determined by conducting field adaptation tests supported by glasshouse and laboratory studies.
There is a need to evaluate plants which grow in saline environments for their suitability for domestication. The evaluation should enable assessment of the possibility of establishing and managing the plants in a given environment and obtaining a sufficient quantity and quality of product in the long term to warrant the effort.
There is minimal information on the benefits derived from rehabilitation of saline environments. Research on erosion control, groundwater use, wildlife conservation and aesthetics may indicate that rehabilitation is warranted irrespective of the yield of forage, fuel or other products.
Vast areas of salt-affected land will remain unproductive unless efforts are made to rehabilitate them with highly salt-tolerant plants (halophytes). A few small beginnings indicate that halophytes will give profitable production on land incapable of supporting other plants. Rehabilitation of saline environments can be facilitated by defining sites in terms of plant growth requirements.
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Table 1. Estimates of the areas of salt-affected soils, (From country reports given at Research for Development Seminar (1985).
|Country or Region||Area||Nature of saline situation||Other factors||Climate/Rainfall (mm)|
|Australia (2) **||2.5||0.3||salt marsh||coastal|
|10.9||1.4||salt pans, salt flats||depressions||< 600|
|0.4||0.05||seepages||300 - 1200|
|14.8||2.0||dry saline lands||no watertable||< 375|
|3.8||0.5||scalds, exposed subsoil||no watertable||< 1000|
|Bangladesh (3)||1.4||16||Coastal pH < 7||Winter months||1500 - 3600|
|Canada (4)||2.2||in great plains|
|Chile (5)||Cl--, SO42-||High boron||Arid|
|Na+, SAR-high Gypsiferous, pH > 7||(7.5-125 ppm)|
|China (6) ***||?||Desert in Northwest||area unknown||< 100|
|20||Semi-arid & arid areas in W. China||salinity & alkalinity or both||< 500|
|3.4||Semi- humid areas||salinity & sodicity||500-1000 seasonal|
|<30||Coastal||shallow groundwater||> 1000|
|Egypt (7)||0.8||25*||Neutral salts, calcareous, gypsiferous soils||High watertable||< 100 arid|
|India (9)||2.1||coastal||High watertable||200-1500|
|1.4||-||black soil||< 550 arid & semi-arid|
|2.5||-||sub-humid, Indo-Gangetic plains||550-900 (July to Sept)|
|Iraq (10) (in Mesopotamian plain)||-||20||Neutral salts, pH 7.2 to 8.2, gypsum (10%), lime (20-30%) organic matter (< 1%).||High watertable||Arid|
|Kenya (11)||8.8||15||Flood plains||50-750|
|Lacustrine plains,||Waterlogging||Arid & semiarid|
|Inland drainage basins|
|Pakistan (12)||2.4||Strongly saline, gypsiferous||100-750|
|2.0||Porous saline - alkali||Highly watertable||Arid & semi-arid|
|0.5||Dense saline - alkali|
|South Africa (13)||-||10.||Neutral salts, pH < 8.2 SAR-high||Drained basins||< 280|
|Coastal pH < 8.2, SAR-high|
|Irrigated lands||Arid & semi-arid|
|Sudano - Sahelian
|Euphrates basin||-||30||Gypsiferous, NaCl dominant pH 8.0-8.4||High boron||< 300 arid|
|Coastal, pH < 7|
|Tunisia (17)||-||-||Inland, gypsiferous,||Arid & semi|
|NaCl/SO4 dominated||-arid 100-600|
|USA (18)||45||5||Saline in western states||Arid & semi-arid|
|40||7*||Sodic, particularly in great plains|
NOTE: Percentages were based on total area of country except as follows:
* figure is % of cultivated area.
** salting of irrigated land in Australia is not included.
*** figure is % of N.E. region only.
(1) - (16) References as follows: (1) Maddaloni (1985); (2) Standing Committee on Soil Conservation (1982); (3) S.M. Ruhul Amin, personal communication, 1984; (4) McKell et al (1985); (5) Squella (1985); (6) Hartley et al (1983); (7) El Lakany et al. (1985); (8) Sissay (1985); (9) Abrol (1985); (10) Abdul, Halim (1985); (11) Kanani 6 Torres (1985); (12) Sandhu and Qureshi (1985); (13) P.A. b. van Breda, personal communication, 1984; (14) Kraiem (1985); (15) Sankary (1985); (16) Limpinuntana and Arunin (1985); (17) El Hamrouni (1985); (18) McKell et al (1985).
Table 2. Examples of types of salt - affected land in different climatic zones.
|Climate||Sea Coast||Endoreic basins||Areas with high watertables||Saline seeps||Upland salt affected areas|
|Cooler humid||-continental cool summer||Not applicable||-||Grand Junction, Colorado;||-||-|
|-continental warm summer||Not applicable||-||Jinan, China;||-||Green River, Utah; salt desert shrub areas, U.S.A.|
|Warmer humid||-marine west coast||Sydney, NSW||-||Victoria & NSW, Australia||Victoria & NSW, Australia;||-|
|-humid sub tropical||Delaware, USA: China;||-||Rio Grande Valley, Texas; E Argentina; Indo-Gangetic Plain India; Victoria Australia; Queensland Australia||-||-|
|-mediterranean||S. Australia||Salt lakes, S.W. Australia;||Southern Australia; Kairouan Plain, Tunisia; Victoria, Australia; surrounds of oasis, S. Tunisia||Southern Australia||Southern Australia|
|Dry||-Steppe||Gujarat India; Kenya; Mediterranean coast, Egypt;||Lake Chad, Chad; Chott el Hodna, Algeria||Northern Great Plains, U.S.A. & Canada: Euphrates Basin, Syria; Alexandria, Egypt; Indo Gangetic Plain, India; Murray River Valley, Australia;||Northern Great Plains, USA & Canada|
|-Desert: hot||Namib; Atacama; Red Sea coast, Ethiopia; Red Sea Coast, Egypt||Salton Sea, Calif.; Lake Eyre, S. Aust.; San Joaquin Valley California; Pampa del Tamarugal, Chile Sabkhats Bouara & Muh, Syria; Danakil, Ethiopia; Qattara Depression, Egypt; Dead Sea, Israel; southern Tunisia;||Indus Plain, Pakistan; W.S. Africa, Nile Delta Egypt, Mesopotamian Plain, Iraq; Rajasthan, India, Gezira, Sudan;||N.E. Kenya;|
|cold||Great Basin, Utah;|
|Tropical humid||-savanna||Saloum River, Senegal; India;||N.E. Thailand; Saloum River, Senegal;|
|-rain forest||Bangladesh; Kerala, India;|
Table 3. Examples of salinity levels in the soil beneath halophytic plants.
|Alhagieto - Erodietum||Syria||400- 800||Sankary (1985)|
|Sphenopus divaricatus||*||1800- 2500|
|Atripleto - Reaumerietum||*||0-25||400- 2500||*|
|Frankenieto - Aeluropetum||*||1400- 4800||*|
|Aeluropeto - Suaedetum||*||4500-10000|
|Maireana brevifolia to||Australia||0-90||1200- 9600||Malcolm (1985a)|
|Distichlis stricta -||USA||0-10||9600-13500||Ungar (1965)|
|Suaeda depressa||60-70||3900- 6500||*|
|Mangrove||Australia||4-8||4420-12180*||Clarke 6 Hannon (1969)|
Table 4. Environmental characterisation of a salt-affected site (from Research for Development Seminar, 1985).
|Minimum Data Base||Additional Characteristic|
|Latitude, longitude, altitude||road position|
|Climatic type||length of growing period wind|
|precipitation type amount (mm,) range, distribution|
|temperature range, distribution by month, frost days and intensity|
|potential evaporation (mm)|
|relief (elevation, range)||geology|
|landscape unit (e.g., coastal swamp,||geomorphology|
|flood plain, seepage area, upland area, etc.)||slope length|
|topography (e.g., summit, upper slope, lower slope,|
|bottom land, etc.) microrelief|
|drainage (internal & external)||source of high watertable|
|flooding (time, duration , frequency)|
|water table conditions (depth, fluctuation, quality)|
|5. Other features|
|cause of salinity|
|locally significant features.|
|Quantification of characteristics for salt affected soils|
|1. Solute concentration of saturated soil extract|
|Electrical conductivity (EC),||dS m-1 or mS m-1|
|Total salt concentration (C),||9 m-3 or mol m-3|
|Osmotic potential (y 0),||J kg-1, Pa, m|
|(per cent salt is not preferred)|
|2. water content|
|Volumetric water content (0),||m3 m-3|
|(gravimetric water content (W),||kg kg-1 is not preferred)|
|Sodium adsorption ration (SAR),||(mol m-3)1/2|
|SAR = CNa /,/ CCa + C Mg where concentration are in units of mol-3|
|Exchangeable sodium percentage (ESP)|
|ESP = 100 CNa/ (Cation Exchange Capacity)|
|4. Specific solutes,||mol m-3|
|Cations :||N+a Ca2+, Mg2+, K+|
|Anions :||Cl, SO24-, HCO3 + CO23|
|Others :||B, Se, F, S.|
|5. pH (specify method)|
Table 5: Natural or introduced species growing successfully on salt - affected land types in various climatic zones
|Types of salt affected land|
|Climate||Sea Coast||Endoreic basins||Areas with high watertables||Saline seeps||Upland salt
humid - savannah
(23 on mine dumps)
Table 5: Natural or introduced species growing successfully on salt - affected land types in various climatic zones - continue
|Types of soft affected fond|
|Climate||Sea coast||Endoreic basins||Areas with high watertables||Saline seeps||Upland salt affected areas|
|Cooler humid||-continental cool summer||Db||Not applicable||-*||-||-||-|
|-continental warm summer||Daf||Not applicable||-||Distichlis stricta, Sporobolus airoides, Suaeda depressa, Spartina pectinata (1)**||-||-|
|Warmer humid||-marine west coast||Cbf||Salicornia europea, Puccinellia maritima, Halimione portulacoides (2)|
|-humid subtropical||Caf||Casuarina glance, Juncus maritimus, Sarcocornia quinqueflora, Avicennia marina var. resinifera, Aegicerus corniculatum, (3) Paspalum vaginatum, (4) Spartina patens, Salterniflora, Distichlis spicata (5)||-||Agropyron elongatum|
|-mediterranean||Csa||Sporobolus virginicus, Atriplex cinarea, A. paludosa (7)||-||Maireana brevifolia, Atriplex amnicola, A. undulata, A. lentiformis, A. nummularia, Halosracia pergranulata (7)||Paspalum vaginatum, Puccinellia ciliata, Tamarix gallica, Agropyronelongatum (7)||Maireana brevifolia (7)|
|Dry||-steppe||Bsh||Juncus acutus, J. rigidus Salaola tetrandra (13)||Phragmites communis (12)||Leptochloa fusca (8), Salsola vermiculata var. villosa (10), Atriplex halimus, A. glauca, Suaeda fruticosa, Haloxylon schmidtii (11), Atriplex undulata, A. lampa (14)||Puccinellia distans (12)||Atriplex Vasicaria, ANummularia (9)|
|-desert hot||BWh||Avicennia marina, Aeluropus sp., Sporobolus spicatus, Suaeda menoica (15) Atriplex undulata, A. amnicola, A. canescens (17) A. farinosa (20)||Suaeda fruticosa, Sporobulus marginatus, Aeluropus lagopoides (16)||Atriplex argentina, A boecheri, A. crenatifolia, A. undulata (14),Aeluropus lagopoides,Sporobolus tremulus (16), Agropyron elongatum, A. leucoclada (20), Salvadora persica (21)||Tamerix gallica, T. pentandra (18)|
Aellenia subaphylla, Haloxylon aphyllum,
Table 6: A guide to the selection of salt - tolerant forage plants for saltland types in Western Australia
|Saltland type||Conditions||Degree of salt affectedness*|
|Saline seeps||Summer wet||Trifolium fragiferum|
|Paspalum dilatatum||Paspalum vaginatum||Paspalum vaginatum|
|Not summer wet||Puccinellia ciliata
|Puccinellia ciliata||Puccinellia ciliata|
|Areas with high watertable||>375 mm rainfall||Puccinellia ciliata**||Puccinellia ciliata||Halosarcia spp.|
|Barley||Atriplex spp. ***||Puccinellia ciliata|
|<375 mm rainfall Commonly flooded in winter||Atriplex spp.||Atriplex spp.||Halosarcia spp.|
|Puccinellia ciliata||Puccinellia ciliata|
|Seldom flooded in winter||Barley Maireana brevifolia||Atriplex spp.||Halosarcia spp.|
|Atriplex spp.||Maireana brevifolia||Atriplex spp|
|Puccinellia ciliata||Puccinellia ciliata||Puccinellia ciliata|
|Upland salt affected areas||Barley||Maireana brevifolia||Maireana brevifolia|
|Maireana brevifolia||Atriplex spp.||Atriplex spp.|
* The degree of affectedness is determined as followsMildly affected saltland has a cover of mediterranean barley grass (Hordeum/geniculatum) and a reduced occurrence of clovers medics and non-salt tolerant grasses. It often gives a reasonable crop with six row barley.
Hoderately affected saltland has a patchy occurrence of bare and grassed areas and only carries a profitable cereal crop if seasonal conditions are especially favourable.
Severely affected saltland is completely bare or only carries highly salt tolerant vegetation such as Halosarcia spp. Cereal crops will not grow on severely affected saltland.
** The preferred plant is mentioned first In some cases a mixture may be sown to cater for different site conditions in patchy areas.
*** Atriplex amnicola & A. undulata are recommended
Table 7. Grazing capacity of planted salt-tolerant forage shrubs.
|Species||Plants per ha||Grazing capacity (sheep/ha/an)||Duration test (days)||Reference|
|Atriplex nummularia||1012||6.0||25 (min)||Jacobs & Smit, 1977|
|Atriplex canescens||1012||1.7||25 (min)||Jacobs $ Smit, 1977|
|Atriplex breweri||1012||2.2||25 (min)||Jacobs & Smit, 1977|
|Atriplex lentiformis||1012||2.2||25 (min)||Jacobs & Smit, 1977|
|Maireana brevifolia||7407||8.1||24||Roux & deKock, 1971|
|Maireana brevifolia, 1st yr*||2500||4.6||42||Clarke, 1982|
|Maireana brevifolia, 2nd yr||2500||2.9||26.5||Clarke, 1982|
|Atriplex paludosa, 1st yr*||2500||5.0||45.5||Clarke, 1982|
|Atriplex paludosa, 2nd yr||2500||3.8||34.3||Clarke, 1982|
|Atriplex rhacodioides, 1st yr*||1111||4.6||42||Clarke, 1982|
|Atriplex rhaqodioides, 2nd yr||1111||4.0||36||Clarke, 1982|
|Atriplex undulata, 1st yr*||1111||5.4||49||Clarke, 1982|
|Atriplex undulate, 2nd yr||1111||4.0||36||Clarke, 1982|
* During the first year 0.5 kg cereal hay was fed per head per day; in the second year there was no additional feed
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