Soil suitability classification by farmers in southern Rwanda

In mountainous areas soil characteristics may Vary within short distances due to the relief. The scale of most soil maps is usually too coarse to take these variations into consideration, thus limiting their usefulness for technology development and extension. Field studies in southern Rwanda revealed that farmers have a profound knowledge of their soils, and classify soils for their own needs. The classification is based on the identification of different soil types according to their agricultural potential and tillage properties. The main criteria applied are: fertility (productivity), depth, structure and colour. Nine major soil types are distinguished. More experienced, older farmers use additional parameters such as indicator plants, texture, consistence and parent material and are capable of further subdividing these types into sub-classes and groups. In the three agro-ecological zones of the study area, situated in different districts, farmers always applied the same names. No clear correlation was found between soil types according to farmers' classification and soil types classified according to Soil Taxonomy. Farmers and scientists appraise soil in different ways. While farmers are interested in soil productivity and appropriate management practices, they take only the topsoil or the arable layer into account. Soil scientists, on the other hand, are also interested in the deeper-lying soil horizons and soil genesis. In addition, farmers' classification is based on local soils and farmers' objectives. Thus names may vary from one region to the other, making comparisons on a (inter)national level impossible. Farmers' soil classes correspond to soil suitability classes, and may therefore be useful for land evaluation systems. The use of vernacular names facilitates exchange between farmers, extension workers and researchers. In order to make practical use of farmers' knowledge, further investigation is required to establish whether farmers in other parts of Rwanda apply the same names and in the same way.