Characterization of drought stress in the major maize production zones of Kenya
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Maize, the most important cereal crop in Kenya, is grown from sea level to more than 2300 m elevation. With the use of geographic information system (GIS) techniques, six distinct maize agro- climatic zones have been defined for the main rainy season in Kenya. The objective of this study was to characterize each of these zones for the degree and timing of drought stress. For each of the six maize zones, two representative sites with extensive weather records were used. Long term means for rainfall for 10 d periods were compared to the potential evapotranspiration of the same period at each site. Maize phenological development was superimposed on these data. In the highland and moist transitional zones, which comprise 75 Per cent of the maize area, drought occurrences were limited. The moist midaltitude zone had the greatest variability in moisture stress between sites, and late season drought is consistently a problem. The dry midaltitude and dry transitional zones experience the most severe drought, especially during grain filling and early in the season. In the lowland tropics, significant moisture stress occurs during the first 20 d of the season and during the last 40 d of growth. These data suggest that drought tolerance is needed for germplasm being developed for four of the six zones.