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Lack of knowledge and evidence to farmers on the benefits of the tree and soil interactions which may halt land degradation on farms often results in the removal of the trees that grow on farms as scattered parklands. An on-farm study was carried out at four sites in Central highlands of Kenya to investigate the effects of selected common tree species on soil organic carbon and pH. Sampling of the top soil was done under the canopies of selected common tree species and from control plots (away from trees). Results revealed that Croton macrostachyus Hochst. Ex Delile plots had a significantly higher (P < 0.01) total organic carbon mean of 2.85% compared to 2.04% obtained in plots under Grevillea robusta A. Cunn. at Kyeni site. Senna spectabilis (DC.) H.S. Irwin & Barneby also had significantly higher (p < 0.05) total organic carbon mean of 2.89% compared to 2.33% obtained in control plots at Kanwaa site. In soil pH, control plots had significantly lower (P < 0.01) mean soil pH values than the plots under selected the trees at all the sites. Among the tree species only G. robusta revealed significantly lower (P < 0.01) soil pH than the C. macrostachyus, Cordia africana and control plots at Kyeni site. The study suggested that S. Specatabilis helps in increasing soil carbon and consequently soil fertility. S. specatabilis, C. africana, C. macrostachyus and Erythrina abyssinicca also showed some positive influence in reducing soil acidification on farms. It is recommended that an increase in the number of trees on farms may improve soil fertility and reduce land degradation.
Ndlovu E Ndlovu E (Tue,) studied this question.