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Wageningen Universiteit (2005)

Farmer’s indicators for soil erosion mapping and crop yield estimations in central highlands of Kenya

Okoba, B.O.

Titre : Farmer’s indicators for soil erosion mapping and crop yield estimations in central highlands of Kenya

Auteur : Okoba, B.O.

Université de soutenance : Wageningen Universiteit

Grade : Doctor Thesis 2005

The central highlands of Kenya is characterised by abundant rainfall and fertile volcanic soils that support agricultural activities but problems of soil erosion are widespread in the region. Past efforts to control the soil erosion problems were through application of regulations that enforced adoption of soil and water conservation measures. Despite many decades of campaigns to have farmers embrace the recommended conservation measures, the success was low and soil degradation continued to increase. Various methodological gaps were identified in the currently applied Catchment Approach concept for soil and water conservation planning. Among these was the lack of simple infield tool to assess soil erosion prior to recommending conservation measures. Currently assessment of soil erosion is largely dependent on expert-experiences and conventional approaches that are resource demanding and hardly simulate local conditions. The aim of this study was to develop a tool for participatory soil erosion mapping at field and catchment scales. This tool is based on the farmers’ knowledge and perceptions of soil degradation and uses farmers’ indicators for soil erosion and sedimentation. Research was conducted in a representative area of the humid highlands of the central Kenya in Gikuuri catchment in Embu District. Through household interviews and focussed group meetings the study established that farmers were aware of the on-going soil erosion problems and they knew various conservation measures despite low adoption. Through their widescale knowledge of the erosion indicators, they were able to present the soil erosion scenario maps comparable to scientific assessments. Crop yield losses were closely correlated to soil erosion indicators as well as to soil erosion status. By reflecting on the catchment soil erosion status map, the farming community resolved to undertake planning of soil and water conservation measures at both the field and catchment scales because they were able to easily pinpoint fields or hillslopes that were severely eroded. The study concluded that lack of involving farmers greatly reduced their motivation to participate in soil and water conservation activities and that using their knowledge of topsoil profile characteristics led to simple approaches of quantifying soil productivity. The last part of this study presents a tool that could be applied to engage farmer(s) to map extent of soil erosion and through which participatory soil and water conservation planning could be realised within the framework of the current Catchment Approach, widely adopted in the East African highland regions.


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