EFFECTS OF MULCHING WITH MULTIPURPOSE-TREE PRUNINGS ON SOIL AND WATERRUN-OFF UNDER SEMIARID CONDITIONS IN KENYA

The effect of adding leaf mulches of Grevillea robusta, Cassia siamea and Gliricidia sepium on the rate of soil and water run-off from a cro p field were studied during two cropping seasons in an alfisol under s emi-arid conditions at Machakos, Kenya. The experiment was conducted i n a randomized complete block design with three replications; two rate s of mulch of each species (2.24 t and 4.48 t, on dry matter basis, pe r ha) and a no-mulch control constituted the seven treatments. Soil an d water Nn-off losses after each major rainfall event and the changes in ground and crop cover were measured. Rainfall erosivity and changes in soil bulk density and infiltration rate were also determined. Soil losses from the plots with mulches of Cassia siamea, Gliricidia sepiu m and Grevillea robusta were significantly lower than those from the c ontrol (p = 0.10). Over the two seasons, the cumulative soil losses fr om plots mulched with cassia, gliricidia and grevillea were 11%, 57% a nd 81% lower than that of the control plot. Similarly, water run-off l osses from cassia, gliricidia and grevillea mulch plots were 28%, 48% and 58%, respectively, lower than that of the control plot. Thus, cass ia was found ta be better than gliricidia and grevillea in reducing bo th soil and water run-off losses. Soil bulk density did not change whi le infiltration rate at the end of the experiment was significantly mo re than in the beginning; however, there were no significant differenc es in these soil physical properties among the treatments.