GIS based multi-criteria analysis for identification of suitable areas for green gram production: a case study of Kitui County, Kenya

Green gram(Vigna radiataL.) has recently become an important crop in Kitui County because of its high economic returns and short growing season.The main objective of this study was therefore to develop a GIS-based Multi-criteria analysis for Green gram production in Kitui County using Geographic Information Sytem (GIS) based multi-criteria evaluation. Three main criteria were selected for analysis (soil, climate and topography) and 8 sub criteria (soil texture, soil depth, soil pH, soil cation exchange capacity, soil drainage, rainfall, temperature and slope). The criteria and subcriteria were selected based on discussions with crop experts and the information available about Green gram requirements from literature. The sub criteria maps were reclassified into 4 suitability levels:Highly Suitable (S1), Moderately Suitable (S2), Marginally Suitable (S3) and Not Suitable(N) based on Food and Agriculture Organisation(FAO) guidelines. The Analytic Hierarchy Process (AHP) decision making tool was used to determine the perceived weights or influence that each criteria and subcriteria carries. The weights were then used as inputs in the weighted overlay and final maps generated. Based on the findings, all the land in Kitui County is suitable for Green gram production in March, April, May (MAM) season with varying degrees of suitability where 4.6% as highly, 54.7% as moderately and 40.7% as marginally suitable. All land is also suitable in October, November and December (OND) with 66.2% being highly suitable and 33.8% moderately suitable. Major limitations that prevent all land from being highly suitable include low rainfall during MAM season, highly acidic and alkaline soils, very poor drainage and steep slopes. Due to the higher potential in OND the County Government should adequately prepare to ensure they maximize on the good environmental conditions for Green gram production.