Systematic evaluation of the effects of the length, depth, and amount of incorporated maize straw on rill flow velocity

Flow velocity is an important indicator when evaluating rill erosion flow dynamics. In recent decades, incor-porating straw in farmland fields has become an effective method of utilizing maize straw resources. However, the effect of straw incorporation on the rill flow velocity of sloping farmland is unclear. In this study, experi-mental treatments with three gradients of maize straw length (6, 9, and 12 cm), incorporation depth (9, 12, and 15 cm), and straw amount (1000, 4500, and 8000 kg ha-1) were set up. Flow velocity was measured via an electrolyte tracer measurement system, and the comprehensive effect of straw incorporation on the rill erosion flow velocity of sloping farmland was clarified using structural equation modeling. The results showed that the mean flow velocity of straw-incorporated sloping land was 0.120-0.189 m s-1, which was 13.25-44.92% lower than that of bare land. The flow path became convoluted owing to the residual straw on the soil surface, which increased the flow resistance thereby reducing the flow velocity. Straw length had the greatest effect on flow velocity (with a contribution rate of 46.67%), and significant increases in velocity were observed with increases in straw length owing to the water-collecting function of the exposed straw on the soil surface. In addition, the flow velocity increased with an increase in runoff and decreased with an increase in infiltration but had no evident response to sediment yield. Increasing the straw amount had a negative impact on soil bulk density and infiltration, resulting in an increase in rill flow velocity. The incorporation depth had a very small effect on flow velocity. The results are helpful for understanding the changes in rill flow velocity and interpreting the soil erosion process on sloping farmland with straw incorporation.