Soil and terrain constraints

The agro-edaphic suitability assessment is based on the comparison of edaphic requirements of rain-fed and irrigated crop/LUTs and prevailing soil and terrain conditions. The edaphic assessment also reflects constraints imposed by landform and other features that do not directly form a part of the soil but may have a significant influence on the use that can be made of the soil. Distinction is made between internal soil requirements of crop/LUTs, such as soil temperature regime, soil moisture regime, soil fertility, effective soil depth for root development, and other physical and chemical soil properties, and external requirements related to soil slope, occurrence of flooding and soil accessibility.

   Agro-edaphic suitability analysis

The results of matching the crop/LUT-specific edaphic requirements to the soil and terrain attributes of individual grid-cells, in combination with calculated potential biomass and agro-climatically attainable yields, provides a suitability classification for each rain-fed and irrigated crop/LUT respectively at high, intermediate and low levels of input circumstances.

In order to safeguard production to be achievable on a sustainable basis, two further considerations are applied in the assessment:

• Fallow requirements are imposed to enable maintenance of soil fertility and structure and counteracting soil degradation caused by cultivation. Fallow requirements vary by environmental conditions, crop, and level of inputs/management (FAO/IIASA, 1991) .  
  
      Fallow period requirements
  

• The terrain-slope suitability classification is concerned not only with workability and accessibility of the land but also with the prevention of intolerable levels of topsoil erosion and fertility loss. Depending on prevailing rainfall aggressivity, level of inputs/management, and crop/LUT, upper limits have been set to slope gradients considered suitable for cultivation.
  
     Terrain suitability evaluation for rain-fed crop production