DIFFERENCE BETWEEN SOIL PROPERTIES OF LAND UNDER CONTINUOUS CULTIVATION AND FALLOW IN 3 SOIL TYPES IN KENYA

A study of the three soils (Nitisols, Luvisols and Andosols) used most in Kenya was undertaken to evaluate the effects of cultivation on the following soil properties: aggregate stability, organic carbon and particle size distribution. For comparison, the soil samples were taken from both adjacent uncultivated fields and fields continuously cultivated under maize crop. The samples were taken at five different depths: 0-10, 10-20, 20-30, 30-40 and 40-50cm. Results of this study revealed considerable changes that had occurred in cultivated soils with regard to aggregate stability, organic carbon and particle size distribution. Aggregate stability was significantly low in cultivated luvisols as compared to uncultivated soils but this was not observed with the nitisols and andosols. A considerable reduction in organic carbon of up to 43% was observed with the luvisol and andosol soils, whereas with the nitisols, a slight increase was observed. The nitisols had been under reduced tillage (strip digging) for three years prior to sampling and the top soil layer (0-10cm) was the most affected. Pulverization of sand particles due to tillage reduced sand content in soils giving rise to high clay content (up to 26%). Eluvation of clay fraction was noticeable in cultivated soils of luvisols and nitisols. Cultivation of soil can therefore lead to soil degradation, especially at the top soil surface, and may eventually give rise to low soil productivity.