Kenya's current 4% rate of population growth requires cultivation of food crops by smallholder farmers in ever drier zones of semiarid lands. Rainfall is limited, variable and unpredictable, but maize, widely known for susceptibility to drought, remains the staple and favorite food crop.
A case study is presented in which “effective rainfall” for Katumani Composite B-type maize, grown at Katumani, Machakos District, is evaluated for each of the 48 wet seasons in the 24-year record. The newly developed analysis takes into account rainfall, evaporation, soil depth and water holding capacity, and growth characteristics of the crop influencing water uptake and yield. Conclusions are:
1) The analysis evaluates suitability of a given crop for production in any location where rainfall and evaporation records are available.
2) Dates of onset of the rains at Katumani are sortable into periods termed “early” (implies expectation of high to medium water adequacy for maize production), “late” (medium to low expectation), and “too late” to recommend planting. These expectations determine recommendations for initial seed and fertilizer rates.
3) Although unpredictable earlier, the rainfall pattern following onset soon sorts itself into one of three categories of water adequacy for maize (high, medium or low). Recommendations for thinning to final plant densities, and for adjusting nitrogen fertilizer rates through sidedressing are based on the perceived category.
4) Approximately two months before harvest, total season effective rainfall can be estimated, and predictions of yield provided to farmers, economists, and other planners concerned with food supplies.
5) An estimate is presented of the value of meteorological information to maize production in Machakos and Kitui Districts.