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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 NH(4)-N, NO(3)-N, and PO(4)-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 NH(4)-N associated with the sediments decreased, in general, with advancing time. However, no corresponding progressive increases of the NO(3)-N concentration in the sediments were observed. The concentrations of the sediments-associated NH(4)-N, NO(3)-N, PO(4)-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 NO(3)-N, PO(4)-P and K. The soil was enriched with NH(4)-N after incorporating straw mulch at 3 Mg ha(-1) and or surface application at 3 and 5 Mg ha(-1).