Identifying the efficacy of undecomposed litter mulch to mitigate runoff and sediment under simulated rainfall conditions

Abstract

The efficacy of undecomposed litter mulch in decreasing surface runoff and soil erosion on slopelands derives from its diminished raindrop impact and increased surface roughness. However, information on their relative importance is limited. Two 10 m-long soil boxes with a slope steepness of 15 % were subjected to a series of simulated rainfalls to investigate the importance, and the experimental treatments included two loam soils, three mulch surfaces (bare soil and litter mulch in contact and not in contact with the soil surface with a same application rate of 300 Mg/ha) and four rainfall intensities (30, 60, 90 and 120 mm h⁻¹). The results showed that compared to the bare plot, the contact and noncontact litter mulch reduced runoff by 35 % and 56 %, respectively, and the reduction decreased with rainfall amount and intensity. The removal of raindrop impact dominated the reduction in runoff, while the contact litter roughness even increased runoff. Contact and noncontact litter mulch reduced sediment yield by 72 % and 50 %, respectively, and the reduction had little correlation with rainfall intensity. The reduction in sediment was mainly attributed to the removal of raindrop impact, and the importance of surface roughness in controlling erosion strengthened under extreme storms. Litter mulch reduced flow velocity by approximately 50 %, and the contact roughness dominates the reduction under intense storms. Litter mulch significantly strengthened the enrichment of fine particles, but reduced the fraction of sand particles in sediment, and the contact roughness dominated the reduction. These results indicate that the removal of raindrop impact plays a dominant role in reducing runoff and erosion on hillslopes and highlight the importance of contact mulch in controlling soil erosion under extreme storms.