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5. Procedures for land resource inventory

5.1 General characterization of the project area
5.2 Topographic data
5.3 Soil survey data
5.4 Climatic and meteorological data
5.5 Water resources data
5.6 Drainage data
5.7 Present land use, vegetation and wildlife
5.8 Environmental health
5.9 Social and economic data

An evaluation of the suitability of land for alternative kinds of use requires a survey to define and map the land units (Step 6 in the Guide to Procedures) together with the collection of descriptive data of land characteristics and resources. This chapter outlines procedures for making a land resource inventory and contains checklists of thematic data that might be required in land evaluation. Details on survey methods are not given but are covered in publications cited in each section.

Data collection is a time-consuming and costly activity, therefore, prior to field activities, members of a project team representing the different disciplines should meet to decide the responsibilities and cooperation needed in collecting and interpreting different kinds of data.

The approach to data collection can be rationalized by posing a few simple questions i.e. What or which data are required? Why are they needed? Where or how can they be collected? Is the cost of their collection worthwhile?

Two major categories of data and information can be defined as follows:

i. data that are available from existing, obtainable records;
ii. data that must be collected during the course of the evaluation through surveys or investigations (including laboratory analysis of water and soil samples).

Data obtainable from existing sources can save valuable time in unnecessary survey or field studies and some of the organizations that can be approached are:

- government departments responsible for: agriculture, lands, irrigation, meteorology, water resources, survey, geological and hydro-geological survey, land titling, land reform, forestry, livestock, conservation, wildlife, botany or botanic gardens; government and quasi-government trading corporations, marketing boards, etc.;

- international banks;

- technical assistance agencies (multilateral and bilateral, e.g. FAO, ILRI, LRDC, ORSTOM, USBR etc.);

- consultants;

- universities, including departments of agriculture, engineering, geography, botany, education, rural development;

- research stations, international and national.

Publications can also be obtained through the retrieval services of major national and international libraries.

The principal categories of data required are dealt with in the following sections under eight headings: general characterization of the project area, topography, soils, water resources, drainage, vegetation and fauna, social and economic data.

5.1 General characterization of the project area

In the initial stages of the evaluation some general data and assumptions about the project area itself should be assembled. The following are usually relevant:

- location and accessibility;
- potential water supplies within or outside the project area;
- main climatic characteristics;
- relief (landforms) and major soil features;
- population and population growth rate;
- standard of living and social values;
- basis of present economy;
- economic infrastructure (e.g. roads, services, markets);
- government subsidies;
- size of farms or other land holdings;
- land tenure systems;
- traditional water rights;
- political system and policies.

A review of these preliminary data will pinpoint the requirements for more detailed inventory and help to identify priorities.

Among the early steps to be taken is to reach agreement amongst representatives of various disciplines on the use of satellite imagery, aerial photographs, base maps and scales (see Table 2). Basic land survey procedures are rarely undertaken without the assistance of aerial photography and remote sensing imagery. It can be assumed that topographic and soil surveys will involve air photo interpretation and ground control, either on traverses or by free ground survey methods. The reader is referred to FAO Soils Bulletin No. 42 (1979b).

The features which can usually be readily identified by stereoscopic examination of paired air photographs include:

i. landforms (flood plains, terraces, residual uplands, dunes, etc.);

ii. surface drainage patterns and systems;

iii. erosional forms and eroded areas;

iv. land use patterns and land use boundaries, sometimes including crop boundaries, and other evidence of human activity Such as roads, railways, habitations, quarries, etc.;

v. major physiognomic types of natural vegetation;

vi. wet areas, including lakes, lagoons and swamps (the latter are not always identifiable);

vii. surface evidence of salt-affected soils;

viii. rock outcrops;

ix. tones (colour changes in colour photography) and patterns which may reflect soil differences and the probable position of soil boundaries.

From this evidence, subject of course to ground checking, a broad understanding of the geomorphology, physiography, surface hydrology and, to some extent, geology of the survey area can be obtained, which is invaluable in developing a sound working legend for land mapping.

In high and very high intensity survey work complete air photo coverage at two scales is very helpful. The first set, at a scale of about 1:40 000 is used for stereo interpretation and for obtaining a general appreciation of the area (a photo mosaic at this, or smaller scales can also be very helpful for the latter purpose). A second set at, or slightly larger than the probable final scale of soil mapping (e.g. at about 1:5 000) is used for some detailed stereo-interpretation but mainly as maps on which soil observations and boundaries can be precisely located in the field. Single photographs can be used for the latter purpose but even in the field more reliable results are achieved by the study of photo-pairs, using a pocket stereoscope.

Air photo interpretation at high intensity levels needs to be checked by adequate ground control at successive levels of detail. This is especially essential where the area is under forest and the maps are to be used for irrigation project design. The early surveys should give guidance on the probable distribution of major soil units, on the selection of areas best surveyed by free survey and/or the best direction and position of traverses, and on areas where more detailed stereo-interpretation of larger scale photographs is likely to be valuable. The emphasis is on ground methods for the remainder of the survey although major assistance in positioning sample points and in checking the likely positioning of boundaries can be obtained by the study of large-scale air photographs in the field.

5.2 Topographic data

Topography is often a major factor in irrigation evaluation as it influences the choice of irrigation method, drainage, erosion, irrigation efficiency, costs of land development, size and shape of fields, labour requirements, range of possible crops, etc. Stable base maps are needed and can usually be obtained from earlier surveys. The ground truth and scale of base maps is particularly important and should be checked especially if the area is under forest cover or dense natural vegetation. Surface irrigation designs require contour intervals to determine slope that should normally be one metre or less, and an appropriate map scale is required. Very detailed topographic data are required for many irrigation structures, especially along routes of probable canals and drains.

Four aspects of topography which have a special bearing on irrigation suitability are: slope, microrelief, macrorelief and position.

i. Slope - Slope may affect the following factors: intended methods of irrigation, erodibility and erosivity, cropping pattern, mechanization problems, exposure to wind, etc. Slope limitations vary greatly from country to country. Critical limits suitable for gravity irrigation and different methods of irrigation are given as guidelines in FAO Soils Bulletin No. 42 (p. 39-43). These apply to situations in irrigated areas similar to those in the USA. In Asia and wet regions, wetland rice is typically grown on steeper sloping land where smaller terraced field sizes are appropriate. The reader is referred to FAO Conservation Guide No. 1 for terrace specifications (Sheng, p. 147, 1977). Contour bench terraces are usually satisfactory for irrigation on slopes up to 3% but on this and steeper land the stability of the terraces and the amount of land lost to bunds should be assessed.

ii. Microrelief - This term applies to minor surface undulations and irregularities of the land surface, with differences in height between crest and trough ranging from 4-5 cm in flat lake plain areas to 4-5 m in areas of wind-blown sand. Estimates of grading and levelling requirements will depend on whether surface, overhead or drip irrigation techniques are used. This is discussed in Part Two C.22. The information required for an assessment of land grading costs includes: cut and fill, the total volume of earth moved, the depth of cut, distance of transport, soil conditions and desired precision of the final grading and type of equipment available. These factors should be related to whether a local contractor with simple equipment is to be used, or whether an international tender will invite contractors with modern sophisticated equipment to undertake the task.

Topsoil depth and subsoil quality may limit the amount of grading that is advisable, or greatly increase the cost if it is necessary to conserve and later respread the topsoil. Some subsoils are unproductive at first, but gradually rehabilitate with irrigation and fertilizer or organic matter applications. In contrast, coarse sands, gravels or layers rich in lime or gypsum (Mousli 1979; Yahia 1982) or exchangeable aluminium may never respond to irrigation after severe truncation.

iii. Macrorelief - Permanent topographic features where slopes change frequently in gradient and direction may influence the choice of irrigation method, field sizes and shape, and land development costs. Field sizes and shape need to be evaluated, especially for gravity and surface irrigation and for mechanized farming.

iv. Position in relation to command area and accessibility - The elevation and distance of the water source often affects the 'irrigable' land area in gravity schemes. The area commanded may be increased by pumping, or by constructing tunnels, inverted siphons and other structures through natural or man-made barriers, or by reservoir construction. Topographic data are often used in evaluating the infrastructural alternatives and their land development costs.

Topographic data are also required in the case of flood hazard and the design of flood protection measures (see Section A.13, Part Two) and for the design of surface or subsurface drainage (see Section 5.6).

5.3 Soil survey data

Collection of soil survey data is dealt with in detail in FAO Soils Bulletin No. 42. Table 14 lists soil characteristics which are often required in the evaluation. Some characteristics may be 'class-determining' and should therefore be given special emphasis; others will be relatively unimportant. Land evaluation for irrigated crops relies on predictions of future soil conditions, therefore the changeable soil characteristics must be evaluated as well as permanent unchangeable characteristics.

Special importance should be given to predicting the maintenance of water in wetland rice fields (see Part Two, A.6.6). Percolation and net irrigation water requirements commonly vary by more than three-fold depending on whether the soil can be effectively puddled. This is therefore an important class-determining factor in many rice areas (see Part Two, A.6).

In drier areas it is important to predict changes in salinity (Part Two, A.8 and A.9), sodicity (A.10) and the watertable (D.28) with sustained irrigation, bearing in mind the other factors involved, e.g. water quality, drainage, rainfall, method of irrigation, crop, farm inputs, etc.

The reader is referred to the references which deal with the various field and laboratory procedures and methods of analysis for determining the characteristics listed in Table 14.1/ Laboratory support for chemical and physical determinations of soils and water should be provided at an early stage. During the initial stages of the evaluation unnecessary analyses can be screened out in preliminary determinations and appropriate intensities of sampling can be decided (Peters 1979). There may be a need for detailed studies on the spatial variability in salinity and other important characteristics.

1/ In particular: Arens and Sivarajasingham 1979; FAO/IBRD 1970; FAO 1979a; Hesse 1971; Loveday 1974; Maas and Hoffmann 1977; Peters 1979; Ponnamperuma 1976; and USDA 1954.

5.4 Climatic and meteorological data

Table 15 lists some of the climatic data commonly required in land evaluation for irrigated agriculture and their uses. Mean monthly meteorological data are generally published for representative recording stations, but it is usually necessary to obtain the original daily data (e.g. of rainfall) over as long a period as possible at the locations of interest. For example, if the benefits of irrigation are to be evaluated, it may be necessary to analyse rainfall data for an existing rainfed situation in order to estimate the present variability in crop production and the influence of dry years and seasonal droughts (see Part Two, A.1). Dates corresponding to the 'start of the rains' and the 'end of the rains' for individual years of the rainfall record, and the occurrence of dry periods during growing periods are often required. Rainfall and other meteorological data are used by hydrologists, agronomists, irrigation and drainage engineers. A multiplication of effort can be avoided by a common approach.

5.5 Water resources data

Investigations of water resources should be considered an integral part of the land resources evaluation process. The activities of those involved (hydrologists, hydrogeologists, engineers, agriculturists and economists) should be appropriately scheduled. Costly water resources surveys in areas where the land later proves unsuitable for irrigation are wasteful; vice versa, detailed land and soil surveys for irrigated agriculture can be wasteful in areas where water supplies later prove inadequate.







Effective soil depth

Root room, water and nutrient retention; land levelling; drainage; aligning and design of irrigation and drainage channels.


Presence of organic or histic horizons

Special problems or opportunities.


Grain size distribution (texture)

For establishing homogeneity of land units and for deriving many characteristics.


Soil structure and porosity
Bulk density. Pore space volume and distribution.
Air-filled pore space at field capacity. Structure stability.

Root environment, nutrient, water and soil management. Drainage and permeability especially of sodic soils. Leaching of excess salts. Tilth and workability for seedbed and land preparation. Ability to puddle riceland. Erodibility.


Infiltration rate

Rainfall and irrigation intake or run-off. Selection of irrigation method. Furrow lengths or basin size. Sprinkler nozzle selection. Erodibility.


Hydraulic conductivity or permeability

Soil drainage, removal of excess water and salts.


Available water capacity (field capacity and permanent wilting point)

Soil water balance, residual water between and following irrigations. Choice of irrigation method and schedules.


Plastic and liquid limits

Indicative of mineralogy and physical behaviour.


Soil strength, linear extensibility

Mechanical strength for construction works; swelling and shrinking; root penetration.




Soil reaction (pH)

To identify very alkaline, sodic and acid sulphate soils; nutrient deficiencies and toxicities.


Carbon and nitrogen

Organic matter content and management.


Gypsum and calcium carbonate

Hardpans, gypsiferous layers liable to subside, gypsum requirements for sodic soils.


Electrical conductivity of saturation extract (ECe)

Salinity hazard.


Soluble salts (Na, K, Ca, Mg, Cl, SO4, CO3 and HCO3)

Interpretation of salinity hazard.


Cation exchange capacity (CEC), total exchangeable bases (TEB) and base saturation %

Nutrient retention and chemical fertility status.


Exchangeable sodium percentage (ESP) or adjusted sodium adsorbtion ratio of saturation extract (adj. SAR)

Sodicity or alkalinity problems.


Exchangeable cations (Na, K, Ca, Mg)

Base saturation, ESP, potassium status.


Available phosphorus

See Table 35, Part Two.


Total contents of P, K, Mg, Na, Cu, Mn, Zn, B, Fe, Al, As, Ni, Cr

Macro and micronutrient content. Toxic elements.




Sand and silt fraction

Indicates parent material and degree of weathering.


Clay fraction and iron and aluminium oxides

1:1 clay minerals less sticky, swell and shrink less and have a smaller surface area (and less CEC) than 1:2 clay minerals. 1:1 clay minerals with Fe and Al oxides predominating may prove excessively well-drained for wetland rice, and often physically favourable but chemically less fertile for non-rice crops.


Calcium and magnesium carbonates

Hardpans restricting rooting depths. Large amounts decrease nutrient retention and fertility; but soils with 60% CaCO3 can be successfully irrigated but with a restricted choice of crops. Deposition under saline conditions of fine grained material blocks pores and reduces permeability. Surface crusting interferes with seedling emergence and infiltration. Lime-induced nutrient deficiencies. Magnesium carbonate soils often very fertile. High exchangeable Mg leads to sodic-like impermeable profile.



Gypsiferous hardpans restrict rooting and make installation of drains and channels difficult. Dissolution may lead to land subsidence after irrigation. Gypsum crystals in soil may offset sodicity tendency. If too high, causes nutrient problems due to unfavourable K/Ca, Mg/Ca ratios and extra costs in fertilizers and soil management.

Note: The characteristics in Table 14 should be evaluated in the context of morphological and geographical considerations.





Climatic class

Reconnaissance and choice of LUT alternatives. See Part Two, Table 30.


- extraterrestrial radiation
- solar radiation (Rs)
- net shortwave solar radiation
- net longwave radiation
- sunshine hours actual sunshine hours (n) daylength or maximum (N) sunshine hours

See Part Two, A.2. Evaporation estimates. Definition of growing period. Crop growth in relation to radiation or light.
The ratio n/N is used to estimate solar radiation if data for Rs is not available.
Crop photoperiodicity.


Temperature (air & ground) Monthly means of:
- daily maximum
- daily minimum
- daily mean
Actual monthly:
- minimum and maximum
Heat units (degree days)
Wet and dry bulb temperatures a.m. and p.m.

See Part Two, A.3.
Reference crop ET estimates. Limiting conditions for cold and frost susceptible crops; heat scorch. Definition of growing periods. Relative humidity and vapour pressure estimates (see below).


Relative humidity
Monthly means of:
- daily a.m. vapour pressure
- daily p.m. vapour pressure

Estimates of evaporation. Disease prevalence. Ripening and maturation of crops. Drying and storage of crops.


Reference crop ETo
- monthly, 10-day, weekly or daily values from climatic data
Pan evaporation
Actual crop evapotranspiration (e.g. from soil-water measurements, computations)

See Part Two, A.6.
Component of water balance estimates for the catchment and of irrigated land; estimates of irrigation water requirements; estimates of reduced crop yields with a deficient water supply.


Precipitation and rainfall
Daily precipitation for as long a period as possible.
Annual mean and S.D.
Monthly mean and S.D., etc.
Rainfall intensity and erosivity
Effective precipitation
Snow, dew

Component of water balance estimates for the catchment and of irrigated land; growing periods; crop yields
Estimates of erosion; crop damage; management problems; mechanization. Estimates of irrigation water requirements.


Wind speed and direction
Weekly means of daily wind speed
Daytime vs. nighttime ratios

Estimates of reference crop ETo.
Estimates of reference crop ETo, adjusted as described in FAO Irrigation and Drainage Paper 24.


Storm incidence
Frequency and intensity

Crop damage; erosion.

The volume of water obtainable for irrigation will depend on the outcome of hydrological studies of surface water, and hydrogeological studies of groundwater (subsurface water). These are the water supply aspects. The water demand aspects include studies and field work to estimate irrigation water requirements and crop water requirements. An important part of the evaluation is the matching of water supplies and water demand (requirement) by mutual adjustments involving cooperative work between water resources specialists, engineers and agriculturists (see Part Two, A. 6).

i. Hydrological studies: Studies may be carried out at national level, at river basin level, at the project development level, and at farm or field level (Horning 1979). Surface water resources may be progressively developed, first using diversion structures to regulate run-of-river stream flow, secondly, with the addition of storage, and later, to full control, including flood control. Existing data, and data collected during the investigations from stream measuring devices (e.g. stage posts, formula-calibrated weirs, current meters and velocity-area rated stations) can be used to estimate run-off and catchment yields, divertible volumes of water, amounts of water for storage, subsurface flows of water, flood peaks and volumes, etc. The reader is referred to standard texts, e.g. for hydrological models, their practical application and limitations e.g. Chow (1964), Clarke (1973).

ii. Hydrogeological studies: Investigations of groundwater resources are generally carried out at the level of the whole hydrogeological basin or aquifer. The studies include observations of water levels and quality in existing open wells and tubewells, and specially drilled observation wells. Mathematical models are usually needed to evaluate the aquifer (e.g. a numerical model which simulates the non-steady state, two-dimensional, groundwater flows). The model can be calibrated using all the available data pertaining to the aquifer in space and time. The input data requirements can be expressed in the form of a flow chart and a programme of work that would lead to a complete hydrogeological assessment including all aspects of the water balance in relation to the characteristics and geometry of the aquifer and the time scale. The output data includes the initial water levels, transmissivities (permeabilities), the specific or storage coefficient, percentage recharge from rainfall, river bed infiltration and the safe yield for irrigation. An example, of such a flow chart is given in Figure 1 (Jacovides 1982). Further surveys and studies are required to establish the precise location of production wells and their water yield for irrigation, the type of well (shallow hand-dug, shallow tubewell, hand-dug with tubewell, deep tubewell, spring or qanat), the depth of the well, borehole lithology and hydrogeological logs. Investigation wells are test pumped to give data including discharge, drawdown, transmissivity, specific capacity (l/s/m), and specific drawdown (m/l/s). The potential water discharge is expressed in litres per second (l/s) which may vary over time according to season or year.

Standard texts that can be referred to are: Bouwer (1978); Todd (1959) and various supplements to Unesco's groundwater studies.

iii. Irrigation water requirements: Meteorological data and field studies are usually necessary to estimate crop water requirement, effective precipitation, run-on, groundwater contribution, soil water storage, run-off, seepage and percolation, conveyance losses, and leaching requirements (see Part Two, A.6 and FAO Irrigation and Drainage Paper No. 24, 1977b). Irrigation water supplies and their control often determine water volumes used by farmers, therefore water management may be as important as physical factors in matching the available supply to the requirements. Irrigation efficiencies in different parts of the world are discussed in Bos and Nugteren (1974).

In rice cultivation, the duration in days of the different operations in land preparation (soaking, seeding, ploughing, harrowing, puddling, transplanting), as well as the related water use for land preparation and transplanting, and the water balance components after transplanting (effective precipitation, evapo-transpiration, seepage and percolation), are the major data that must be specified (see Part Two, A.6).

For crops other than rice similar gains and losses of water need to be quantified together with the need for pre-planting wetting and allowances for the use of residual soil water as annual crops mature.

Figure 1 Simplified flow chart of a groundwater model programme showing inputs and outputs

iv. Water quality data: Water quality for agricultural use can be evaluated using field and laboratory analyses of the properties listed in Part Two, Tables 37 and 38. Analytical procedures for these determinations are described in USDA Handbook 60 (1954), FAO Soils Bulletin No. 10 (1970), and Standard Methods of the American Water Works Association (1971). The electrical conductivity of, and other simple tests on, samples of irrigation water can be measured in the field using portable conductivity bridges, pH meters and testing kits. For example, having tools-of-the-trade for the testing of groundwater in wells obviates the need for transporting water samples. Local analyses of carbonate, bicarbonate and nitrate may be required where storage of samples may lead to chemical changes and inaccurate results.

In arid and semi-arid areas it will be necessary to predict the salt balance and the water balance for a project area to evaluate leaching requirements, and the drainage needed to maintain the land in a productive condition. In rehabilitation projects, water samples may be analysed at different points of the network. The flow of water and salts in an irrigated area are illustrated in Figure 18 (see also Part Two, D.27). Special analyses will be required for recycled sewage where it is intended for irrigation. The biological oxygen demand (BOD), chemical oxygen demand (COD), boron, heavy metals and other potentially toxic substances must be ascertained. Bacterial analysis may also be necessary. Routine analyses are normally part of the procedures of the water treatment plant. Sewage or activated sludge can be subjected to primary, secondary and tertiary treatment. Analyses of chemical constituents, suspended solids and dissolved organic substances are required to evaluate whether water from secondary or tertiary treatment can be used for irrigation, and the potential problems in handling such water.

Water for drip irrigation and for other techniques where there is a potential clogging problem can be evaluated on the basis of measurements of the suspended solids and chemical or biological properties of the water (see Part Two, Table 38).

Guidance on the interpretation of water analyses is given in FAO Irrigation and Drainage Paper No. 29 (1976c; Revision 1 in press) and other publications.

5.6 Drainage data

Conditions and requirements for surface drainage, subsurface (pipe) drainage, or both may need to be evaluated. In arid and semi-arid areas, where salinity and sodicity are possible problems, it will be essential to carry out field investigations. The soil scientist and drainage engineer should first agree on the types and scales of maps and photographs to be used and on the information that will be placed by each on these. Field hydraulic conductivity and other tests are required; the number of tests for a drainage survey is related to the soil variability in the project area (FAO Irrigation and Drainage Paper No. 38, 1980a). This variability is initially assessed from surveys in sample areas that cover 5-10 percent of the project area from representative major soil units. Local experience and sound judgement will often be needed to determine an average hydraulic conductivity value for the design of drain spacings, sizes and depths. This particularly applies to the drainage of heavy, poorly permeable soils under crops other than rice.

Drainage investigations in arid and semi-arid areas will involve the logging and sampling of 3-5 m borings to identify barriers with a relatively low hydraulic conductivity compared to overlying soil or a high resistance to vertical flow (i.e. C = 250 or over constitutes a real barrier, whilst no barrier exists where C = 50 or less: C is the hydraulic resistance and equals the thickness of the layer divided by its vertical hydraulic conductivity).

Much data useful to the drainage study may be obtained in soil survey (e.g. reliable soil profile logs to 3-5 m; depth to watertable or visible indications of saturated conditions; water quality, soil salinity, sodicity and acidity). Soil survey information will make it possible to interpolate hydraulic conductivity measurements to intermediate soils. Therefore, where possible, the soils and drainage investigations should proceed concurrently. The soil scientist should bring areas of potentially poor drainage to the attention of the drainage engineer. These may include visibly wet areas, areas visibly saline or sodic, topographically low areas, areas with fine textured layers within a 5 m depth; slowly permeable layers within a 5 m depth; massive structure not usually associated with the identified texture; man-made barriers which could impede surface drainage or groundwater movement; potentially unstable materials, especially gypsiferous layers (the latter may lead to subsidence and irrigation and drainage construction problems with a high water table). It is usually the responsibility of the drainage engineer to determine the investigations required for estimating the cost of the surface and subsurface drainage systems and related flood control facilities. The estimated costs can be tabulated by areas and used in the evaluation of land suitability class and the delineation of the irrigable land.

If the land cannot be physically drained because of low hydraulic conductivity, or because of barriers too close to the ground surface, it should be excluded at the 'provisionally-irrigable' stage. In the 'irrigable' land evaluation, physical drainage can be envisaged to meet the water table requirements, but land may still be excluded for economic reasons. Later, if the drainage areas are small in comparison to the rest of the area and a properly designed and located drainage system for the irrigable area cannot be installed without going through such lands, the classifier has the option of retaining these lands as suitable in the 'provisionally-irrigable' and 'irrigable' classifications. These considerations are important in determining the extent of the drainage investigations.

Drainage requirements and costs for surface, subsurface, and related flood control should be made available by the drainage engineer for all 'provisionally-irrigable' lands but no subsurface drainage or flood control requirements and costs need normally be provided for lands! initially rated N1 or N2, for reasons other than drainage.

The reader is referred to FAO Irrigation and Drainage Paper No. 38, (1980a) and the USBR Drainage Manual (1978). Part Two of this bulletin, sections C.20 and C.21, give further information on land evaluation for drainage and drainage system design.

5.7 Present land use, vegetation and wildlife

Many land evaluations will be carried out in areas which are partially covered with natural vegetation and partially farmed. The geographical extent of vegetation and the existing agriculture should be studied early in the evaluation mapping where necessary. Present land use surveys are generally required to determine the production which will be foregone when an irrigation project is implemented.

Existing vegetation and present land use may be important because of:

i. costs of clearing different kinds of vegetation (see Part Two, C.19);
ii. potential value of the vegetation, e.g. for forest and grazing;
iii. presence of noxious weeds;
iv. need to preserve vegetation for environmental, aesthetic reasons;
v. value of present agricultural production;
vi. preferences for continuing present production on certain lands.

Needless removal of vegetation due to inadequate survey and beaconing often occurs. Areas of natural vegetation should be preserved wherever possible.

Close liaison with departments responsible for environmental protection is generally essential to ensure that the boundaries of national parks and wildlife conservation zones are respected. The preservation of natural vegetation as windbreaks may prove important. Damage by wildlife in farmers' fields may necessitate costly measures such as fencing. Hippopotamus, warthog and bush pigs in African countries are fairly easily excluded but large game requires very costly fences. Monkeys and baboons are almost impossible to exclude leaving a choice between poisoning or shooting. Bush can also harbour tsetse, while the introduction of irrigated perennial crops, e.g. bananas, can promote the spread of tsetse. Irrigation can also be a barrier to seasonal animal movements. Information collected on potential problems from wild animals, including rodents, birds, crabs, etc. may dictate the choice of crops and LUTs. Rodents and crabs may bore holes in the banks of canals and the bunds of ricefields leading to excessive losses of water. Factor ratings under heading A.12, Part Two can be used to evaluate the potential damage to crops, stored products and infrastructure from wildlife.

5.8 Environmental health

Failure to consider the environment when evaluating irrigation development may result in an increased incidence of disease among the local human population, especially of vector-borne diseases such as malaria, schistosomiasis (bilharzia), onchocerciasis (river blindness) and yellow fever. The vectors are certain aquatic snails, flies and mosquitoes which host the disease-causing parasite and transfer it from the infected to the healthy individual. These agents need water to breed and multiply; thus the expansion of irrigation spreads the diseases through the irrigation networks, particularly in areas where the water is used for domestic purposes as well. The need for environmental control measures through the design of reservoirs and canals and the prevention of unnecessary vegetation or pools of stagnant water should be assessed. Further information is available from the joint WHO/FAO/UNEP Panel of Experts on Environmental Management for Vector Control (PEEM) and from FAO 1984. The general subject of the environmental health consequences of irrigation are discussed by Worthington (1977).

5.9 Social and economic data

5.9.1 Social and economic considerations
5.9.2 Checklist of socio-economic data

Social and economic evaluations depend on survey work which should usually start early in the land evaluation process. The objectives of the survey work are to identify and assess the social and economic features affecting the development potential of the study area and to evaluate alternative proposals; to assemble financial and economic price and cost data of relevance in the assessment of LUTs and class-determining factors; and to meet the analytical and reporting requirements of the sponsor of the given study (e.g. World Bank etc.).

The socio-economist may need survey data collected by agriculturists and vice versa (i.e. on present farming practices and production, land use, farm inputs etc.) and there can be some sharing of survey activities based on prior agreement. Present land use surveys are generally required to determine the production that will be foregone when an irrigation project is implemented. Trends in production, land use and yields need studies, particularly where rehabilitation of existing irrigation and drainage systems is being considered. Where there is a trend of rising or falling production this, rather than a static assessment of the present situation, should form the basis of predictions of the 'without' situation in the economic evaluation (see Chapter 7).

5.9.1 Social and economic considerations

Some of the considerations that may prevent the full utilization of natural and human resources are listed below. These are often outside the control of the individuals affected by them and constitute many of the constraints to agricultural and social progress.

i. Self-perpetuating poverty: Lack of venture capital, knowledge, and the will to adopt new technology is characteristic of subsistence level farming where meeting today's needs may be the practical limit of forward planning.

ii. Tradition, attitudes and perceptions: Viewpoints of the possibility of change in order to control one's own destiny better may be entirely formed on extremely limited observations, those being the only ones known to an individual. The situation beyond could be so obscure as to have no effect upon the subject's aspirations for something better.

iii. Disincentives: Crop production goals may be limited by quotas, and prices may be controlled at below the cost of production; under such circumstances little more than the level of output required for subsistence and local barter may be produced.

iv. Tenure: Land ownership and tenurial rights together with water rights are often a major cause of maldistribution of income and wealth. Access to credit and production inputs may be linked to tenurial patterns. Unfavourable tenurial conditions may restrain the natural economic forces that normally determine efficient farm size, and crop selection.

v. Food preferences: These limit the range of crops grown for local consumption, especially where a market outlet has not been developed. A degree of crop or livestock specialization may have developed around the local food preferences.

vi. Labour supply: The existing labour supply and the seasonal labour peaks may limit the range of land use possibilities. The labour supply may be limited in its present technology because of failure by the younger generation to participate. A new technology could lead to their participation.

vii. Pricing systems: Controlled or artificial prices may constitute either a disincentive or an incentive. If a price is controlled to the point that the production is discouraged, one must look for a possibility that this could be changed if it is of importance to a project.

If these types of unfavourable conditions exist, they could well prevail into the future and continue to influence strongly what farmers would do under an irrigated system of farming. Therefore, proposed changes to traditional farming systems require a full appreciation of the reasons why present agricultural patterns exist.

Furthermore, a judgement is necessary on how rapidly and to what extent favourable changes could occur when irrigation is introduced. Forecasted changes ought to be not only economically favourable, but they must also be likely to occur and not just be speculative. Whilst it may be helpful to develop plans that appear economically optimal, in reality what will be achieved is nearly always short of the optimum. That which is likely to be achieved should be projected in the values assigned to future productivity. In-country and regional experiences on similar projects may prove to be the best key to this. These should be observed closely.

Social and economic constraints can frequently be removed at a cost. Project cost estimates may include outlays for training, resettlement, infrastructure, markets and other items considered necessary to achieve the levels of productivity forecasted.

Some activities that may be required with the introduction of irrigated farming may be incorporated in the project plan, at least during the gestation period or build-up to full development, for example:

- inputs must be increased and made available;

- research, extension and the dissemination of technical knowledge might need to be expanded;

- transportation, storage and other infrastructure may need to be developed; fuel and power demands may increase and need to be satisfied; marketing facilities may be required; credit and financing needs, and protection against the risks of commercialized farming may have to be considered.

Favourable features of prospective farmer groups might include a demonstrated capacity to accept new agricultural methods, community and cooperative endeavours aimed at social change, responses to financial incentives, initiatives and diversified farming enterprises, etc. Such information may be available from the experience of ongoing and past agricultural programmes.

5.9.2 Checklist of socio-economic data

A comprehensive list of data that may need to be collected in social and economic survey work is given in Table 16 (adapted from IRRI 1975c). The reader is also referred to standard texts on procedures for social and economic survey work (Yang 1965) and to Chapter 7 on the economic aspects of land evaluation for irrigated agriculture.






District or Village levels


Crops and varieties planted in the area
List of present LUTs, include cultivars classed as high yielding, modern, improved local, or traditional; cropping calendar (pre- & post-harvest)


Farm practices
Planting methods, fertilizer, organic manures, insecticides, herbicides, weeding; hand, animal or tractor power; land preparation, mechanization, changes in practices


Existing irrigation and drainage
Types of irrigation systems; periods of water availability, persons or authorities controlling water allocation; drainage adequacy; water use


Input-output data
Costs of all inputs, yields and value of produce whether used for subsistence, barter or cash sales; crop disposal


Land tenure, farm sizes, land values, water rights
Land tenure, leased and shared cropped land, titles to land and water, fragmentation, social contexts, land sales, land prices


Credit and loans
Amounts borrowed, who borrowed from whom, credit for personal or farming use, in cash or kind, duration of loan, terms of repayment or interest rate, level of indebtedness, future access to loans


Household size and income
Farm family size and age distribution, employment on and off the farm; sources of income; changes in income


Farm labour and employment, farm power
Family labour, hired labour, labour costs; influence of labour, power and water on land preparation, seasonal practices; peak labour requirements changes


Production and marketing problems
Obtaining seed, fertilizer or chemicals, credit, water (domestic, irrigation); pests and diseases, weeds, harvesting, threshing, drying, storage, selling, processing, others; markets



National Regional District and Village levels


Roads and waterways; availability of buses, trucks, carts, boats, and other modes of transportation; railroads, quality of roads - paved or not; year-round use, etc.


Storage, processing and marketing facilities
Types that serve the villages in project area; driers, milling capacity, local weights and measures, milling outputs etc.


Banks and other credit facilities


Other government facilities for production
Research and experimental stations; demonstration trials; extension services


Schools, clinics, postal services and others


Communications media
Press, radio, and other forms of mass media, extent of news of direct relevance to farmers, markets news service




Domestic water supplies



National Regional District and Village levels


Prices of major produce, differences between cultivars, seasonal and annual variations; prices at nearest dealer or cooperative for fertilizer and other major inputs; data on price differentials between local and major markets


Wage rates; systems of wage payment; changes over time


Rates usually paid on loans from different sources; changes over time


Rates per season, year, and others; in cash or kind; fixed or shared; changes over time


Types and totals; paid to village or other agency; changes over time


Land prices
Average, for major land types; changes over time


Irrigation costs
Government irrigation fees and normal collection rates; normal cost of private irrigation systems, if any


Seed or planting material
Availability, source, quality, and prices


Typical farm power requirement and investment for land preparation, also rental rates for tractor and animal services





National Regional District and Village levels


Village populations
Total, and percentage changes in last 10 years; main sources of livelihood, farming and non-farming


Other census data
Religion, ethnic group, castes, and others


Village settlement pattern
Along road, with house gardens, cluster, isolated, etc.



National Regional District and Village levels


Farmers' organizations
Cooperatives, farmer associations and similar bodies; other types of joint or group activities, changes over time


Brief description of the way new crops, varieties and methods of management were introduced into the area


Extension services, also credit, and other services
Number of agencies that provide services; quantity and quality of services; main complaints of farmers


Special government programmes
Land reform, land consolidation, crash programmes, and others


Role in inheritance, cost of ceremonies, etc.; also factionalism, litigation, etc.


Leadership in agriculturally relevant activities


Attitudes and values affecting development
Change in the size and cost of ceremonies; evaluation as to whether farming is a preferred occupation and similar assessments



National Regional levels


Aims of national policy for crops and irrigation


Policy measures
Price policies - input and output; restrictions on input and output marketing, if any; package programmes, etc.; income and employment policies - income redistribution, access to land resources, etc.


Importance of new crops and irrigation in the context of national goals

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