The methodology of assessing land suitability for rainfed production, developed by the FAO Agro-ecological Zones Project is described in FAO (1978–81), and is summarized in Figure 2.1. It comprises of the following activities:
Selection and definition of land utilization types (e.g. crop type, produce, production system, input level).
Determination of climatic requirements of crops.
Determination of soil and landform requirements of crop.
Compilation of a quantitative climatic resources inventory characterizing thermal regimes (thermal zones) moisture regimes (length of growing period zones and historical pattern of number of growing periods per year).
Assemblage of a soil resources inventory, providing information on soil type, texture, stoniness, phase (if any) and slope.
Compilation of a land resources inventory, by overlaying the climatic inventory on the soil inventory, and measurement of resultant climate-soil land units.
Calculation (from iv, v and vi) of extents of soil units (by slope class, texture class, stoniness and phase) by thermal zone, length of growing period zone and pattern of growing period zone.
Matching the thermal zones of the climatic inventory (iv) with temperature requirements of crops, and where these requirements are met, computation of constraint-free crop yields by length of growing period zones.
Compilation of the agro-climatic constraints to crop production by length of growing period zones and thermal zones.
Application of the agro-climatic constraints (ix) to the constraint-free crop yields (viii) to derive agronomically attainable crop yields, by growing period zones.
Agro-climatic suitability classification of each growing period zone according to anticipated crop yields (x).
Matching the soil requirements of crops (iii) with the soil types,texture classes, stoniness, phases and slope classes of the soil inventory, by rating soil limitations (agro-edaphic suitability classification).
Computer application of the soil limitation ratings (agro-edaphic suitability classification) on the agro-climatic suitability classification of each growing period zone, to arrive at the land suitability classification, i.e. extents of land variously suited to production of the crop at each input level.
According to the methodology outlined above, the agro-climatic suitability classification involves activities (i), (ii), (iv), (viii), (ix), (x) and (xi), and the agro-edaphic suitability classification involves activities (i), (iii), (v) and (xii).
