Determination of the best planting season for green grams in Kitui county, Kenya, using the analytic hierarchy process

Abstract

Green gram is a short duration crop that is traditionally grown in arid regions and has recently become a flagship value chain crop in Kitui County because of its high economic returns. The purpose of this study was to analyse the spatial variation of rainfall and temperature in the county, and their effects on green gram production. The Analytical Hierarchy Process (AHP) decision making tool was used to determine the perceived weights or influence that rainfall and temperature have on green gram production using information from literature and experts. Seasonal rainfall totals and seasonal mean temperature for the Long rains (March-May; MAM) and Short rains (October-December; OND), were calculated from Worldclim data while the rainfall and temperature requirements for green gram were determined and grouped into four classes based on FAO (1976) guidelines. Using this information the green gram growing potentials were determined and corresponding maps generated. Results of the weighted overlay of rainfall and temperature show that during MAM 4.9%, 33.9% and 61.3% of land in Kitui County are highly, moderately and marginally, suitable for green gram production, respectively. During OND, two classes emerge with 75.6% and 24.4% of land in Kitui County being highly and marginally suitable, respectively. Due to the higher potential in OND the farmer with the support of the government should adequately prepare to ensure they maximize on the good environmental conditions.