Each agro-ecological cell with given soil, terrain and LGP characteristics was tested
on the computer for its suitability for growing each of 30 crops under three levels of
technolgy: e.g. lom, intermediate and high. The resulting yields for each cell, crop and
technology alternative were then compared with those obtainable under the same
technology and LGP characteristics on land without soil and terrain constraints (termed the maximum constraint free yield-MCFY). Any agro-ecological cell so tested is classified as suitable for rainfed crop production if at least one of the crops could be grown under any one of the three technology alternatives with a yield of 30% or more of the MCFY for that technology. If more than one crop meet this criterion, the amount of land is classified as suitable as determined on the basis of the crop which utilized the greatest part of the land in the cell. The extent occupied by that crop defined the extent of arable land. Any piece of land not meeting this criterion is classified as not suitable. The land classified as suitable is further classified into three suitability classes as follows: very suitable (at least 80% of MCFY); suitable (40 to 80% of MCFY); marginally suitable (20 to 40%). Plate 13 presents a map of potential rain fed arable land for Africa.