The effects of tillage induced surface roughness, slope and discharge rate on soil detachment by concentrated flow: An experimental study

Soil erosion in sloping cropland is a key water and soil conservation issue in the Loess Plateau region, China. How surface roughness influences soil detachment remains unclear due to the inconsistent results obtained from existing studies. The objectives of the present study were to evaluate the effects of tillage practices on soil detachment rate in sloping cropland and establish an accurate empirical model for the prediction of soil detachment rates. A series of movable bed experiments were conducted on sloping surfaces under three different tillage practices (manual dibbling, manual hoeing, and contour drilling), with a smooth surface (non‐tillage) as a control. The research indicated that soil detachment rate significantly increased with roughness (p < 0.05) since the average soil detachment rate was the highest under the contour drilling treatment (6.762 g m⁻² s⁻¹), followed by manual hoeing (4.180 g m⁻² s⁻¹), and manual dibbling (3.334 g m⁻² s⁻¹); the lowest detachment rate was observed under the non‐tillage treatment (3.214 g m⁻² s⁻¹). Slope gradient and unit discharge rate were positively correlated with soil detachment rate and proved to be more influential than soil surface roughness. Four composite hydraulic parameters were introduced to estimate soil detachment rate on tilled surfaces. Regression analyses revealed that stream power was the most effective predictor of soil detachment rate compared with unit length shear force, shear stress, and unit stream power. By integrating surface roughness as a variable, the detachment rate could be accurately described as a nonlinear function of stream power and surface roughness. The results of the present study indicate that tillage practice could influence soil loss on sloping cropland, considering the higher soil detachment rates under all tillage practices tested compared with non‐tillage. The results are attributed mainly to concentrated flow caused by the high water storage levels on tilled surfaces, which could damage surface microtopography and, subsequently, the development of headcuts.