Influence of trees on soil characteristics and maize productivity in small holder farms of western Kenya

Maize production in Kenya has been decreasing with time, especially in Western Kenya which is one of the main belts of maize production. This is due to low purchasing power for inorganic fertilizers by resource poor farmers. Use of local inputs such as tree and shrub biomass that are easily available in the farms may be a realistic option to improve soil fertility. This study evaluated the effect of four tree species (Grevillea robusta, Leuceana spp, Markhamia lutea and Mangifera indica) on soil pH, CEC, TOC and on growth and yield of maize. The study was done on pre-selected farmer groups in Bungoma and Siaya by the ongoing Sustainable Intensification of Maize Legume cropping system for food security in Eastern and Southern Africa (SIMLESA) project. A baseline survey was conducted to determine common tree species growing on farms. Farms with common trees growing along the farm boundary were selected. The trees species that were used for the study were Grevillea robusta, Leuceana spp, Markhamia lutea and Mangifera indica. Soil samples were randomly taken at a 1 m radius using a soil auger for three distance intervals, that is, 2, 7 and 12 m distance away on the ground from each of the selected tree and mixed thoroughly to come up with a composite sample for each treatment. This was repeated for two other trees of the same species in the same farm. Sampling was done at two levels, namely 0-15 cm (top soil) and 15-30cm (sub soil). The soil samples were analyzed for soil pH, soil TOC and soil CEC. Soil pH, CEC and TOC did differ significant (P>0.05) at the different distance intervals for all the tree species. Results on maize growth indicated that the crops under the canopies of G. robusta, Leuceana spp and M. indica had suppressed growth compared to those that were few meters away while crops close to the canopies of M. lutea performed better compared to those that were some distance away. Eucalyptus spp, Markhamia lutea and Grevillea robusta were the most preferred trees. From the study, it’s evident that trees affect the chemical properties of soil,that is TOC, CEC and soil pH and all the trees suppressed plant growth and yield except M lutea. Therefore more research on the potential of M lutea as an agroforestry tree and how it affects the soil properties since it had a different trend from other trees.