4.1 Deciding and describing the land utilization types to evaluate
4.2 Developing the land suitability class specifications
This Chapter covers Steps 1 to 5 of the guide to the procedures outlined in Chapter 3, and concerns the choice of alternative farming systems (LUTs) and the requirements and limitations of these LUTs.
4.1.1 Examples of irrigated LUTs
4.1.2 Some problems in defining and describing LUTs
The first two steps elaborated in the first part of this Chapter have already been listed in Chapter 3, i.e.
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Step 1: Land is evaluated with respect to its suitability for a given land use. Decide the alternative land uses (i.e. LUTs or farming systems) of interest and prepare to evaluate each of these separately. Step 2: Describe the LUTs. For each LUT, complete a description based on headings given in Table 10. |
The activities in land evaluation that are specifically concerned with the choice and evaluation of cropping, irrigation and management systems (i.e. with land use) start with decisions about the alternative LUTs that will be separately evaluated.
The FAO Framework recognizes two levels of detail at which land use is defined:
- A major kind of land use represents a major subdivision of rural land use such as extensive agriculture, intensive agriculture, grassland, forestry, or recreation.- A land utilization type (LUT) is a kind of land use defined in more detail, according to a set of technical descriptors (see Table 10) in a given physical, economic and social setting. (Note the similarity between the terms 'LUT' and 'farming system' in an agricultural context.)
Land utilization types (or farming systems) are described in as much detail and precision as the purpose requires. In low intensity studies their descriptions may be general and short, while later during more intensive studies the detail included in the description increases.
The FAO Framework distinguishes between single, multiple and compound LUTs:
- A single LUT specifies only one kind of use undertaken on an area of land (e.g. irrigated rice, or irrigated sugarcane, or irrigated tree crops).- A multiple LUT specifies more than one kind of use simultaneously undertaken on the same area of land, each use having its own inputs, requirements and produce. An example is irrigated rice grown under coconuts in parts of South-east Asia.
- A compound LUT specifies more than one kind of use sequentially undertaken on the same area of land. Examples are winter and summer cropping of wheat and cotton in irrigated areas of the Middle East; or wet season rice followed by other crops in the dry season, in South Asia.
Table 10 CHECKLIST OF HEADINGS FOR DESCRIPTION OF LAND UTILIZATION TYPES
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|
HEADINGS |
DESCRIPTIONS |
|
i. |
Cropping system |
Single, multiple or compound LUT. Crops grown, cultivars, cropping calendar, cropping intensity. Perennial cropping systems, cultivation factor, cropping index. (See Glossary) |
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ii. |
Markets |
Subsistence, commercial or both, domestic or export, or both. |
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iii. |
Water supply |
Seasonal supply and quality. |
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iv. |
Irrigation method 1/ |
Gravity or lift, run-of-river or storage releases, surface, overhead, drip, etc. |
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v. |
Capital intensity |
Value of capital investment and recurring costs per ha. |
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vi. |
Labour intensity |
Family and hired labour, man-months per ha, seasonal peak periods, festivities and holidays |
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vii. |
Technical skills and attitudes |
Experience, response to innovation and change, literacy |
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viii. |
Power |
Extent of human, animal and tractor power impact on land preparation, harvesting, etc. |
|
ix. |
Mechanization and farm operations |
Which operations are mechanized or partly mechanized. |
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x. |
Size and shape of farms |
Farm size, size by LUTs, fragmentation of holdings, rainfed and irrigated areas. |
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xi. |
Land tenure |
Freehold: family farm, corporately owned estate. |
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Tenancy: cash rent tenancy,, labour tenancy, share cropping. |
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Communal ownership: cooperative (collective) farming, village land with rights to cultivate, etc. |
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State ownership: state farm, national park. |
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xii. |
Water rights |
State or private ownership, traditional purchases and sales of water. Local laws (e.g. FAO, 1978). |
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xiii. |
Infrastructure |
Assumptions about processing facilities, storage depots, markets, access to farm inputs. Roads, housing, schools, medical facilities, electricity, domestic water supplies. Research and extension services and facilities. |
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xiv. |
Irrigation infrastructure |
Assumptions about irrigation and drainage infrastructure and access to irrigated land. |
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xv. |
Material inputs |
Prior assumptions about quantities and quality of inputs especially for seed, planting material, fertilizers, pesticides, herbicides, etc. |
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xvi. |
Cultivation practices |
Preparation of land for irrigation including clearing. |
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Tillage operations (including duration for ploughing, levelling etc.) |
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Fertilizer application (timing and methods), weeding, crop protection, harvesting and processing. |
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xvii. |
Livestock |
For traction, milk or meat, manure, forage requirements, including crop by-products, field grazing, zero grazing, stall-fed, etc. |
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xviii. |
Associated rainfed |
Influence of LUT of competing rainfed agriculture, forestry agriculture, shifting cultivation or agro-forestry, timber trade from land cleared for irrigation. |
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xix. |
Yields and production |
Yields per unit area on S1 land (ceiling values for relative yield). |
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Yields per unit of water (per m3) especially during periods of water shortage. |
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(Specify mean yields with confidence limits, or ranges suitable for economic and financial sensitivity analyses.) |
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Land equivalent ratio, income equivalent ratio. |
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xx. |
Environmental impact |
Public health problems (i.e. bilharzia, malaria, river blindness, diseases transmitted by water). |
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Downstream effects on water supply and quality, siltation, flooding, etc. |
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Effects on wildlife conservation. |
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xxi. |
Economic information |
Market prices, input costs and availabilities, subsidies, credit (see Section 5.9, Table 16). |
1/ For the characteristics of surface, overhead, drip and other irrigation systems see Part 2, Table B48.
Sometimes the LUT is obvious from the outset of the evaluation (e.g. irrigated rice). In other projects the prospective alternative land uses are unclear at the start of the study and LUTs are first identified in a tentative and general way. As the survey proceeds and as new quantitative data are acquired, the LUTs are progressively defined in detail. The cropping, irrigation and management aspects of the LUT are modified with inputs and land improvements to obtain a satisfactory match between the requirements or limitations of the LUT, and the conditions of the land. The aim of irrigation development projects is to leave the nation, community and farmers better off, therefore it is also generally necessary to make a comparative evaluation of the existing and proposed farming systems (i.e. LUTs without and with the project).
Table 10 gives a checklist of headings for the description of LUTs. Some of these descriptors may be common to groups of LUTs, while others are specific to an individual LUT. The number of aspects to be described, and the detail of descriptions under each heading, depends on the scale and objectives of the survey. In rapid reconnaissance surveys, some descriptors may be omitted or noted only briefly. Conversely, in intensive studies, the details under some headings may run to a page or more.
A few brief descriptions of LUTs are given as illustrative examples as follows:
i. Irrigated rice (mapping symbol LUT-2R), two crops of 140-day short-strawed high yielding cultivars; gravity, run-of-river water supply, no seasonal or annual shortages of water. Smallholders with low capital reserves, using animal-drawn farm implements, high labour intensity, 50% freehold farms, 50% tenants, farms about 1-2 ha. Subsistence and domestic markets. Anticipated yields of 8 t/ha/yr of paddy rice on S1 land.ii. Irrigated rice (wet season) followed by soybeans (dry season), mapping symbol LUT-RS. The soybeans are relay planted and are grown chiefly on residual moisture after irrigation supplies dry up. Yields are increased where supplementary groundwater is supplied from tubewells, but this is only possible at some locations, hence water supply is 'class-determining' in the 'irrigable' evaluation. Company estates, 150 ha farms, capital intensive, labour shortages, mechanized tillage and harvest. Anticipated yields 3 t/ha paddy and 1.5 t/ha soybeans on S1 land.
iii. Irrigated winter crops (wheat, beans, clover) followed by irrigated summer crops (cotton, maize, sorghum), mapping symbol LUT-WS. Cropping intensities anticipated of 175%. Smallholder farms of 2.5 ha on leased reclaimed saline desert in government-owned communally managed estates. Water supply (EC = 1.5 dS/m) to be pumped to 10 m elevation. Water supplies are to be on a rotation at 7-day intervals. Mechanized land preparation but all other operations by hand, farm inputs available but no credit. Parts of area near centres of population can substitute vegetables in the rotation. Anticipated yields 50% of potential but could improve with time. Potential yields on S1 land could be given in an accompanying table.
iv. Sprinkler irrigated sugarcane, mapping symbol LUT-SC. Nucleus estate of 4 000 ha (outgrowers sugarcane described under a separate LUT). Anticipated capital investment in years 1-3 of $6 000/ha, with annual recurrent costs of $500/ha from year 3. Three to four ratoons, anticipated yields on S1 land from 90 t/ha for the first crop and decreasing to 60 t/ha for the fourth ratoon. Private company in joint venture with government for the supply of sugar to meet domestic requirements. Pumped water to be supplied following harvest until wet season starts. Hand cutting, mechanized loading and transport, mechanized tillage. Factory milling and the economics of processing is of importance in the economic evaluation of the irrigation scheme.
v. Drip-irrigated citrus on farms of 10-80 ha, supplemental irrigation with rainfall in farmers' fields expected to supply about one-third of the crop water requirement directly. Mapping symbol LUT-DC. In dry years water will be withheld from certain areas of land and water supply reliability is a 'class-determining' factor. Water quality varies from EC = 1.0 to 3.5 dS/m, and together with water supply affects yields which may vary from 7-50 t/ha for mature trees on land classed as Suitable (precise cut-off point between S and N to be determined in the evaluation). Orchard life 40 years, intercropping in the first four years with winter crops (beans, vegetables, etc.) on winter rainfall. Mechanized cultivation, labour shortages in the harvesting season, limited market expansion expected.
vi. Spate irrigation of sorghum (mapping symbol LUT-SS). Rainfall 400 mm with a variation, i.e. standard deviation of 250 mm. Irregular, largely uncontrolled water supply, 8 000 ha can receive irrigation in a wet year, but generally very unreliable on about half the area. Competition for water between potential users. Traditional water rights have been abused resulting in disputes. Yields very dependant on soil water storage and residual water after irrigation, and range from 0-5 t grain/ha. Low capital investment, labour shortages, no mechanization. Resistance to change, elaborate tenurial system. Land evaluation in relation to improvements in the diversion structures.
The number of LUTs that can be separately evaluated in any investigation is limited. The investigator may be faced with a choice between the selection of many detailed LUTs, or fewer generalized LUTs. This can be illustrated by reference to Table 11 which lists a grouping of LUTs in terms of broadly defined major groups, and progressively detailed subgroups and sub-subgroups. The land evaluator has a choice between selecting the major headings, the subheadings, or the sub-subheadings as LUTs. In this particular case, the cropping pattern is closely linked to the available water supply at different times of the year. Land which can receive water all-the-year round can support two crops of rice per year, whereas land which can receive water for only part of the year can support only one rice crop followed by another food crop, or with even less water, one crop of rice, only. The investigator has to choose, therefore, between evaluating the water supply as a class-determining factor or specifying the water supply as a descriptor of the LUT. The more general the LUT definition, the more important is the water supply in the determination of land suitability classes, in this particular example.
A further problem in describing LUTs can arise in the choice between alternative irrigation methods, for example, between surface irrigation and sprinkler irrigation. Surface irrigation involves land development costs (land levelling, etc.) that are not incurred under sprinkler irrigation, but the latter involves capital costs including pipes, sprinklers and pumping costs. If the sprinkler investment costs are not set off against the land development costs for surface irrigation, because they are described as part of the LUT, a false economic comparison could result. Therefore, investment costs have to be considered as 'class-determining' alongside land development costs where comparisons of this importance must be evaluated.
Table 11 LAND UTILIZATION TYPES IN BALI (IRRIGATED) 1/
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1. |
IRRIGATED LANDS |
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1.1 |
Irrigated rice only |
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1.1.1 Two crops of local 140-160 day varieties per year 2/ |
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1.1.2 Five crops of short duration 120 day varieties per two years |
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1.1.3 One crop of 140-160 day local variety followed by one crop of 120 day local or new variety per year (where dry season water is limited) |
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1.1.4 One irrigated rice crop (wet season) and land fallow in dry season (where soil is unsuitable for palawija crops and there is insufficient water for second rice crop) |
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1.2 |
Irrigated rice (wet season), irrigated or rainfed palawija (dry season) 3/ |
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1.2.1 Rice, rice, palawija per year 4/ |
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1.2.2 Rice, palawija, palawija per year |
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1.2.3 Rice followed by one relay-planted soybean crop per year |
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1.2.4 Rice followed by one palawija crop other than soybeans. |
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1.3 |
Irrigated rice under coconuts |
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1.3.1 Rice (wet season), palawija or fallow (dry season) |
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1.3.2 Rice, rice per year |
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1.4 |
Irrigated palawija crops only Palawija crops rarely irrigated because of serious weed problems |
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1.5 |
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1.5.1 Pure stand citrus |
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1.5.2 Citrus under-planted with maize, groundnuts and red onions |
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1/ Eavis and Walker 1976.2/ Rice is usually transplanted under groups 1.1, 1.2 and 1.3 but direct - seeding is a possible future variant. Days refer to time from transplanting to harvest.
3/ Palawija is an Indonesian term that collectively refers to crops grown in rotation with rice, e.g. maize, groundnuts, green gram (mung), tobacco, red onion, soybeans, sweet potato, melon, cucumber etc.
4/ Generally relay-planted, i.e. sown in rice stubble or before rice is harvested, without any cultivation.
In reconnaissance studies it may suffice to include inputs as a descriptor of the LUT rather than as class-determining factors (e.g. LUT A with high inputs vs. LUT B with low inputs, etc.). Further refinements in the evaluation of LUT A with high inputs, using net farm income or NIIB would almost certainly necessitate incorporating the inputs or land improvements as class-determining land use requirements and limitations (see Section 4.2).
The land evaluator must define his LUTs so that within any one LUT there will be variations in physical productivity or in the economic measures of suitability of land, which can be designated into different classes. One LUT may not produce as much net farm income or net incremental irrigation benefit on a given land unit as another LUT, and may be downgraded on the basis of economic criteria (see Section 2.4 and Chapter 7) unless appropriately combined into a multiple or compound LUT.
4.2.1 Steps in developing the land suitability class specifications
4.2.2 Class-determining factors (step 3)
4.2.3 Land use requirements and limitations
4.2.4 Critical limits of 'class-determining' land use requirements and limitations
The land suitability classes (S1, S2, S3, N1, or N2) which express the suitability of land for a specified use, can be evaluated in terms of a land productivity index based on physical production (e.g. t/ha) or in terms of economic returns. Regardless of which measure of suitability is used, the evaluation always involves decisions about the physical suitability of a land unit for a given LUT. If the physical conditions of the land are uniquely related to the performance of the land in terms of an economic index within any given project area, specifications can be set down for each land suitability class in terms of the land characteristics. Thus the US Bureau of Reclamation uses specifications of soils, topography and drainage characteristics corresponding to each land class on the assumption that these are uniquely correlated with estimated levels of net farm income or payment capacity.
In a worldwide context, the specification of land suitability classes in terms of a few universally applicable land characteristics is not sound. The land conditions that are suited for the production of crops vary from place to place. Different crops, irrigation methods and management systems have differing requirements. Even within a project area combinations of characteristics are often important (e.g. one soil type may be best at the top of a slope, and another soil type best at the bottom of a slope in terms of a given crop or management requirement or limitation). In developing class specifications, therefore, it is more appropriate in the first instance, to specify the land suitability classes in terms of land use requirements and limitations rather than directly in terms of land characteristics. The need for inputs and land improvements should also be taken into account. Later, if good correlations are proven between the land characteristics and the physical and economic indices of suitability, this process can be short-circuited.
Following from Steps 1 and 2, given in Section 3.1, the next Steps 3-5 concern developing the specifications of the requirements and limitations of the cropping, irrigation and management systems of each LUT to be evaluated:
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Step 3: From the list of agronomic, management, land development, conservation, environmental and socio-economic factors given in Table 12, select the relevant 'class-determining' factors that can be expected to have some influence on the suitability of land for the given LUT, and that may vary across the land units under study. Step 4: For each selected 'class-determining' factor, enter the appropriate land use requirement or limitation on Format 1. Step 5: Quantify 'critical limits' corresponding to s1, s2, s3, n1 and n2 levels of suitability for individual land use requirements and limitations. These are the specifications for each factor in terms of the requirements or limitations of the LUT. These specifications can be represented by appropriate land qualities, or their representative land characteristics, together with the inputs and land improvements which influence productivity, net farm income or NIIB. Enter the 'critical limits' on Format 1, thus separating the suitability levels for each individual factor. |
In setting up land suitability class specifications prior to an evaluation of land units for a LUT, the investigator must decide which factors are 'class-determining'. Class-determining factors affect the performance of the LUT on the land units under study, i.e. yields, benefits and costs. Furthermore, they affect these differently on different land units, whereas a much larger number of factors will affect the LUT equally or with only unimportant variations across all the land units under study in a given evaluation. During an evaluation the number of factors that are class-determining will be shortlisted, and later their influence will be aggregated in a yield or economic index.
Individual factors, that may or may not be selected as 'class-determining' in any given evaluation, can be grouped according to how they affect:
a. crop yields or crop production (i.e. agronomic factors)
b. management
c. land development or land improvement
d. conservation and the environment
e. social and economic conditions
These broad groups may be further subdivided for convenience to give a list of 32 individual factors as shown in Table 12.
In the first instance, 'class-determining' factors can mostly be represented in terms of the requirements or limitations of the cropping, irrigation and management systems described in a LUT. The crops require light and suitable temperatures, a continuous supply of water and nutrients, a suitable environment for root growth, suitable conditions in a seedbed for germination, suitable land conditions for irrigation or for harvesting, mechanization, post-harvest ripening, etc. Conversely, crops are variously limited by their susceptibilities or tolerances to excess water, excess salts or toxicities, deficiencies, pests, frost, storms, etc. Similarly, irrigation methods such as surface, sprinkler, or drip have their different requirements and limitations, as do management systems (e.g. manual vs. mechanized). These are some of the land use requirements and limitations that may be 'class-determining'.
The 'class-determining' land use requirements and limitations can be entered on Format 1.
The approach recommended is to indicate on Format 1, the critical ranges, bounded by critical limits, that specify for each individual class-determining factor, the land use requirements and limitations for different levels of suitability s1, s2, s3, n1 and n2. For example, the water requirements of the cropping system can be specified as the depth of water and its timing to meet evapotranspiration and other losses. If the requirement is not fully met, the crop yield will be affected in a way that can be predicted using production functions such as for example, are given in Part Two, Figure 11. Production functions describe the relationship between the agronomic requirements and limitations and crop yield or quality as further discussed in Part Two. Critical ranges for levels of suitability must be derived from such relationships.
Experimentally, good relationships have been found between the supply of water, nutrients, light and heat to a crop and its growth and yield. However, the relationship between the performance of a crop and land characteristics such as soil texture, structure, cation exchange capacity, rainfall, slope class, drainage class, etc. are generally indirect and less clear. Nonetheless, many requirements and limitations of the cropping, irrigation and management systems will be influenced for better or worse by conditions of the land and can be specified as land qualities; these land qualities can be represented by relevant groups of land characteristics. The latter can be designated by the investigator as the feature of the land he can physically measure or assess to assign 'critical limits'. Guidance on how to select land qualities and land characteristics to represent the land use requirements and limitations is given in Part Two of this bulletin.
The setting of critical limits in terms of each factor individually can be assisted by answering three questions:
i. How do the conditions of the land (i.e. land qualities and land characteristics) relate to the land use requirements and limitations?ii. Should inputs (e.g. fertilizer, labour, etc.) or land improvements (e.g. land levelling, etc.) be specified, and if so should these be included as part of the description of the LUT or as a 'class-determining' factor due to a variable benefit/cost?
iii. What are the output:input relationships, first in physical terms (e.g. yield vs. water deficiency) and secondly, in economic terms?
These questions are discussed in Part Two.
A list of land use requirements and limitations and their corresponding land qualities is given in Table 12 and the relation between them will be immediately apparent. Some of the land characteristics, inputs, land improvements and other considerations that influence the suitability of a land unit for a given LUT, are also listed in Table 12.
Table 13 indicates how class-determining factors should be rated by setting critical limits for s1, s2, s3, n1 and n2 levels of suitability.
Table 12 LIST OF CLASS-DETERMINING FACTORS (i.e. AS LAND USE REQUIREMENTS OR LIMITATIONS OR AS LAND QUALITIES) WITH SOME LAND CHARACTERISTICS, INPUTS AND LAND IMPROVEMENTS FOR CONSIDERATION IN SETTING CRITICAL LIMITS
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CLASS-DETERMINING FACTORS: 1/ |
REPRESENTATIVE LAND CHARACTERISTICS, INPUTS, LAND IMPROVEMENTS AND OTHER RELEVANT CONSIDERATIONS (see Part Two for full explanations) | |
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A. |
AGRONOMIC: |
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|
1. |
GROWING PERIODS: |
Growing cycle of crops. Dates and duration (days). |
|
2. |
RADIATION: |
Day length, extra-terrestrial radiation; solar radiation (Rs); photo-synthetically active radiation (PAR); actual sunshine hours (n); possible number of sunshine hours (N); net shortwave radiation Rns; total net radiation (Rn) mm of evaporation (Rn = 1 cal/cm2/min approximate equivalent to 1 mm water/hr). |
|
3. |
TEMPERATURE: |
Temperature data. Heat units. Frost free periods. |
|
4. |
ROOTING: |
Effective soil depth for roots. Root room. Volume percent of stones. Penetration resistance or soil strength. |
|
5. |
AERATION: |
Periods with or without adequate aeration during the growing period. (Depth and fluctuation of groundwater) |
|
6. |
WATER QUANTITY: |
Water balance, water storage. Yield vs. evapotranspiration relationships; deficient periods. Run-off, run-on, seepage and percolation, groundwater contribution, effective precipitation. Stream flows, diversions, storage releases, aquifer safe yields. |
|
7. |
NUTRIENTS (NPK) |
NPK uptake by crops and responses to NPK. Losses of NPK (leaching, volatilization, fixation, etc.). Nitrogen fixation. Soil nutrients and their retention, cation exchange capacity, etc. Fertilizer requirements and availability including manures, etc. |
|
8. |
WATER QUALITY: |
Total salt concentration. Ionic composition. Electrical conductivity dS/m at 25 °C. Sodium adsorption ratio (SAR). pH, carbonates and bicarbonates. Suspended solids, BOD, COD, etc. |
|
9. |
SALINITY: |
Plant salt tolerances, present and future soil salinity, inputs of salt through water supply, losses of salt by leaching, salt balance. Seasonal salt movement in profile, salt from groundwater. |
|
10. |
SODICITY: |
Predicted pH, ESP and or SAR of soil solution, predicted effects on soil structure, infiltration and permeabilities. Sodium toxicity. |
|
11. |
pH, MICRONUTRIENTS AND TOXICITIES: |
On non-rice cropland, pH effects and crop tolerances and susceptibilities to excesses or deficiencies of Ca, Mg, Zn, Fe, S, B, Cu, Mn, Mo, Al. On submerged soil effects of pH, salts, Fe, Si, Mo, Zn, Cu, H2S. Soil and plant composition, relevant inputs. |
|
12. |
PEST, DISEASE, WEEDS: |
Crop tolerances and susceptibilities. Wild animals, birds, arthropods etc. Fungal, bacterial, viral pathogens. Weeds. Pesticides, fencing, inputs. |
|
13. |
FLOOD, STORM, WIND, FROST: |
Adaptations of rice to flooded conditions. Frequency and severity of flood, storm, wind, frost and hail. |
|
B. |
MANAGEMENT: |
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|
14. |
LOCATION: |
Closeness to markets, processing units. Access to inputs and services. Access to water (gravity, pumped). Travel & transport problems & cost. Day-to-day management problems. Accessibility of machinery. |
|
15. |
WATER APPLICATION MANAGEMENT: |
Size, shape of management units. Labour requirement availability. Conditions affecting uniformity of water application, rate, frequency and duration of application. |
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16. |
PRE-HARVEST FARM MANAGEMENT: |
Effects on timing of pre-harvest operations (e.g. of soil workability) including land preparation, nurseries, seeding, transplanting, fertilizer application, irrigation, weeding, spraying, etc. |
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17. |
HARVEST AND POST HARVEST MANAGEMENT: |
Atmospheric wetness, dryness, wind. Soil wetness, dryness. Effects of soil or humidity on the quality of the crop produce. |
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18. |
MECHANIZATION: |
Slope angle, rock hindrances, stoniness, soil depth, soil texture, shape and size of fields. Effects of soil compaction. On-farm transportation. |
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C. |
LAND DEVELOPMENT AND IMPROVEMENTS |
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19. |
LAND CLEARING: |
Forest: underbrushing, felling, burning, stacking; costs, value of timber, charcoal; time period to development. Persistent weeds: mechanical cultivation, flooding, chemical control; costs, time period to development. Rocks and stones: removal costs. |
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20. |
FLOOD PROTECTION: |
Earthmoving costs for embankments, costs of structures. |
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21. |
DRAINAGE: |
Watertable depth, depth to barrier of low permeability, vertical resistance to flow through soil and barrier, slope angle, need for salt removal; size, spacing, depth of surface or pipe-drainage and cost of drainage. |
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22. |
LAND GRADING AND LEVELLING: |
Slope, microrelief, macrorelief, cover. Field size and shape, cut and fill, earthmoving costs. |
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23. |
PHYSICAL, CHEMICAL AND ORGANIC AIDS AND AMENDMENTS: |
Need for deep ploughing, subsoiling, profile inversion, sanding, marling; gypsum, lime, organic matter, costs. |
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24. |
RECLAMATION LEACHING: |
Primary or one-time reclamation leaching requirements mm of water; continuous or intermittent, costs. |
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25. |
DURATION OF RECLAMATION PERIOD: |
Number of project years to full production, project year in which field drainage is installed, rate of rise in watertable. |
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26. |
IRRIGATION ENGINEERING: |
Earthwork and other structures for diversion, storage, conveyance, and regulation of water. Topography, substratum conditions, permeability of channels, access to construction sites, costs of engineering works. |
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D. |
CONSERVATION AND ENVIRONMENTAL: |
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27. |
LONG-TERM PREVENTION OF SALINITY AND SODICITY: |
Long-term inputs and outputs of salts, (see Fig. 18), water quality, ground-water depth, permeability, drainage, tidal swamp conditions, intrusion of saline water into an aquifer, control measures and their cost. |
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28. |
LONG-TERM CONTROL OF GROUND-WATER AND SURFACE WATER: |
Protection of catchment areas, degradation of catchment, sedimentation of reservoirs, control of groundwater, and their costs. |
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29. |
EROSION HAZARD: |
Erosion control. Maximum acceptable soil loss and effects of climate, soil, topography, land use factor, costs. |
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30. |
ENVIRONMENTAL HAZARDS: |
Wildlife, water-borne human diseases, need for environmental control of vectors. |
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E. |
SOCIO-ECONOMIC: |
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31. |
FARMERS' ATTITUDES TO IRRIGATION |
Will the farmers utilize the irrigation facilities? |
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32. |
OTHER SOCIO-ECONOMIC LIMITATIONS THAT MAY BE CLASS-DETERMINING |
Water rights, tenurial and land-ownership complications, disincentives of taxation, fragmentation, etc. |
1/ Evaluate only selected factors i.e. those that are class-determining in a given evaluation.
Table 13 RATINGS OF CLASS-DETERMINING FACTORS (FACTOR RATINGS)
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FACTOR RATINGS |
GUIDELINES FOR SETTING CRITICAL LIMITS |
|
s1 |
The critical limits indicate that in terms of the given factor, the land is highly suitable for the specified land use. |
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s2 |
The critical limits indicate that in terms of the given factor, the land conditions are slightly adverse for the specified land use. |
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s3 |
The critical limits indicate that in terms of the given factor, the land is marginally suitable for the specified land use. |
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n1 |
The critical limits indicate that in terms of the given factor, the land is marginally not suitable for the specified land use (usually for adverse benefit/cost reasons). |
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n2 |
The critical limits indicate that in terms of the given factor, the land is permanently unsuitable for the specified land use. |
Note: Critical limits to define factor ratings should reflect benefit/cost or other economic indices that indicate the influence of the factor on the value of production, costs of production, land development costs, etc.
