Impact of tillage-induced microtopography on hydrological-sediment connectivity and its hydrodynamic understanding

Tillage-induced microtopography may affect hydrological and erosion processes. Nevertheless, how the tillage practices affect hydrological-sediment connectivity at the plot scale remains unclear, and there is little hydrodynamic understanding of soil erosion control by tillage practices. Rainfall simulations under three rainfall intensities (1.0, 1.5 and 2.0 mm min−1) and slope gradients (10, 15 and 20°) were implemented in three 4.0 by 0.8 m soil boxes with different microtopographic patterns (smooth (CK slope), medium rough (AD slope), and rough surface (RT slope)). This study coupled the relative surface connectivity function (RSCf) and the index of connectivity (IC) to assess the impacts of microtopography on hydrological-sediment connectivity. The results showed that soil microtopography delayed the runoff generation and hindered the development of hydrological processes on a gentle slope with low rainfall intensity (10°, 1.0 mm min−1). The impact of microtopography on hydrological connectivity gradually reduced when rainfall intensity and slope increased. The sediment connectivity was higher on the AD slope, followed by the RT slope, and then on the CK slope. The formation of rills significantly enhanced sediment connectivity on the tilled slopes. The critical hydrodynamic parameters required for soil erosion initiation increased with the increase in microrelief. For the CK slope, critical flow shear stress, critical stream power, and critical unit stream power were 1.214 Pa, 0.151 N m−1 s−1, and 0.002 m s−1, respectively. For the AD slope, the corresponding critical hydrodynamic values were 2.505 Pa, 0.205 N m−1 s−1, and 0.003 m s−1, respectively. For the RT slope, the corresponding values were 3.323 Pa, 0.267 N m−1 s−1, and 0.005 m s−1, respectively. The results can provide a valuable reference for analyzing soil erosion mechanisms in sloping farmland.