Abstract: Understanding the effects of upslope runoff and soil pipe collapse on slope water erosion can provide scien-tific basis for preventing Mollisol degradation caused by soil erosion. We conducted an experiment to investigate the effects of upslope inflow rate and soil pipe collapse on slope water erosion and to quantify the contribution of soil pipe erosion to slope soil erosion. The experiment included three inflow rates (30, 40, and 50 L·min^-1) and three near-surface soil hydrological conditions (without soil pipe: NP; with soil pipe but no pipe flow: PF₀; with pipe flow: PF₁). The results showed that: 1) Slope soil erosion increased with increasing inflow rates; when the inflow rate increased from 30 L·min^-1 to 40 and 50 L·min^-1, slope soil erosion increased by 100.0%-111.5% and 214.8%-289.2%, respectively. 2) The soil pipe occurrence and pipe flow formation aggravated the slope water erosion process. At inflow rates of 30, 40, and 50 L·min^-1, slope soil loss under the PF₀ and PF₁ treatments were 1.4-1.6 times and 1.7-2.1 times of that under the NP treatment. The contribution of soil pipe erosion to slope soil loss was 26.7%-37.6% under the PF₀ treatment and 40.5%-51.9% under the PF₁ treatment. 3) Soil pipe collapse intensified the rill erosion process. Compared with the NP treatment at 30, 40, and 50 L·min^-1 inflow rate, rill erosion amounts under the PF₀ and PF₁ treatments increased by 38.1%-66.0% and by 93.7%-128.4%, respectively. Our results suggested that increasing upslope inflow rate resulted in higher surface runoff velocity, which promoted runoff detachment and transport capacity, and then aggrandized the amount of slope soil erosion. Moreover, soil pipe collapse exacerbated rill erosion process. When the soil pipe collapsed, all surface runoff was converted to soil pipe flow, which accelerated flow velocity and slope soil erosion process, and then increased the amount of slope soil erosion.

Key words: upslope inflow, soil pipe collapse, slope water erosion, Mollisol region