Undecomposed litter mixed in the soil can increase interrill erosion on hillslopes: A laboratory study

Abstract

Soil-litter mixing has been found to affect soil erosion. However, previous studies did not distinguish the effects of litter exposed on the soil surface and that buried in the soil resulting from soil-litter mixing processes. This causes an unclear understanding of the effect of soil-litter mixing on soil erosion. In this research, we hypothesized that after mixing, the exposed litter would decrease soil erosion, while the litter buried in the soil would increase soil erosion. To test this hypothesis, soil boxes were filled with three treatments: soil-litter mixing with surface-exposed litter (CS), soil-litter mixing without surface-exposed litter (S), and soil surface cover (C) at four litter rates (0, 0.10, 0.20, and 0.35 kg m−2). Laboratory rainfall experiments were performed under a soil box slope of 10° and at a rainfall intensity of 80 mm h−1. The results of this study showed that the CS and C treatments reduced runoff velocity, and their velocities changed similarly depending on the surface cover of litter. However, in the S treatment, the litter rate increasedid not change runoff velocity significantly, indicating that runoff velocity was mostly controlled by the litter on the soil surface. Under the same surface cover, the C treatment reduced sediment yield by up to 39%; while the S treatment was found to increase sediment yield by up to 43% compared with the bare soil. The sediment yield of the CS treatment showed a decreasing trend as the litter rate increased. When the litter increased to 0.35 kg m−2, the sediment in CS treatment was 19% lower than in the bare soil. These results demonstrate a counteracting effect of surface litter and buried litter. The promoting effect of the buried litter on sediment yield was explained by the undecomposed litter creating an oversaturated condition and introducing a deforming force that decreased soil resistance to erosion. This study suggests that it is necessary to isolate the effect of exposed litter and buried litter on soil erosion, particularly in the early period after soil-litter mixing when litter is undecomposed.