Effect of straw mulch application on nutrient concentration in runoff and sediment in a humid region in Kenya

Abstract

Straw mulch use has been studied extensively especially for soil erosion and runoff control in arid and semi-arid regions but few studies have been done with regard to nutrient loss and accumulation in humid climate regions in Africa. The objective of the present study was to investigate the effects of straw mulch application using different methods on nutrient loss and accumulation in a humid region in Kenya. Straw mulch was applied to runoff plots at 0, 3 and 5 Mg ha-1, either incorporated into the 0 to 0.2 m soil layer or placed on the soil surface. The concentration of NH4–N, NO3–N, and PO4–P in the runoff decreased exponentially and significantly with advancing time. The K concentration in the runoff followed a hyperbolic pattern with a minimum value between 33 and 55 days after planting. In all the treatments, the concentrations of the NH4–Nassociated with the sediments decreased, in general, with advancing time. However, no corresponding progressive increases of the NO3–N concentration in the sediments were observed. The concentrations of the sediments-associated NH4–N, NO3–N, PO4–P and K in the mulch treatments were higher than those in the control, although these differences were not significant in all the rainstorms. Under this humid climate, either surface placement or incorporation of straw mulch at 3 or 5 Mg ha-1 enriched the soil with NO3–N, PO4–P and K. The soil was enriched with NH4–N after incorporating straw mulch at 3 Mg ha-1 and or surface application at 3 and 5 Mg ha-1. Key words: Erosion, nutrient accumulation, nutrient loss, sediment enrichment, water quality.