Effects of residue mulch rate and placement on infiltration, runoff and soil loss of a nitisol

Abstract

The effects of residue mulch rate and placement on infiltration, runoff and soil loss was stu~ied under natural rainfall on a 16% slope of humic nitisol at Kabete, Nairobi, Kenya. The study had five treatments which were replicated three times. The treatments were, distributed mulch at a rate of 1.5 t/ha, distributed mulch at a rate of 3 t/ha, lined (trashlined) mulch at a rate of 1.5 t/ha, lined (trashlined) mulch at a rate of 3 t/ha, and control with no mulch. In total, there were 15 plots, each of 2 m by 10 m. Maize crop residues were used. Two way analysis of variance (ANOVA) and Duncan' s multiple range test were used in comparing the treatment effect on infiltration, runoff and soil loss. The experiment was cropped with beans during, the short rains 1992. Maize planted during the long rains 1993 failed due to drought. Results showed that: ,The mulch treatment effect was significant in increasing infiltration and reducing runoff and soil losses. Distributed mulch at 3 tjha, lined mulch at 3 tjha, distributed mulch at 1.5 tjha and lined mulch at 1.5 t/ha reduced soil loss by 78 %, 74 %, 60 % and 50 % of that from the unmulched (control) plot respectively. Further, 1ined mulch at 3 tjha, distributed mulch at 3 tjha, distributed mulch at 1.5 tjha and lined mulch at 1.5 tjha reduced runoff volume by 69 %, 67 %, 54 % and 44 % of the control's runoff respectively. Infiltration depth was deepest in lined mulch at 3 t/ha followed by distributed mulch at 3 t/ha, distributed mulch at 1.5 t/ha, lined mulch at 1.5 t/ha and control respectively. Analysis of variance (ANOVA) showed that there were significant differences in runoff and soil loss among the treatments at P=l%. Comparison of the treatments using Duncan's method showed that only the control treatment was significantly different from the mulch treatments at P = 0.05. However, there was no significance difference in infiltration depth among the treatments. The mulch treatments significantly increased crop yield. Comparison of the treatments using Duncan's method showed that yield from the control was significantly less than that obtained from treated plots at P = 0.05. It was concluded that use of low cost soil and water conservation methods, like use of crop residues, should be encouraged. Where crop residue is scarce, low rates should still be used as they will be better than nothing. Where crop residue is abundant, high rates would have a beneficial effect. Depending on the availability of crop residue, labour, and type of farm operations which take place, a farmer could be advised to use either distributed or lined mulch at 1.5 t/ha or 3 t/ha. However, where only very small quantities of mulch are available, the farmer could be advised to use it together with other conservation methods as it has been shown that small quantities of mulch will not- be adequate to control soil and water losses during heavy storms. All these would enable the resource poor farmer to control soil and water losse. and eventually increase crop yield.