Impact of Cornstalk Buffer Strip on Hillslope Soil Erosion and Its Hydrodynamic Understanding.

Soil erosion is still a serious concern on the Loess Plateau despite extensive soil conservation measures. Cornstalk buffer strip is not well utilized on the Loess Plateau, and there is little information on the hydrodynamic understanding of this soil erosion control practice. A simulated rainfall experiment was designed to investigate how cornstalk buffer strip affected soil erosion on the typical steep slope of the Loess Plateau. Large soil beds (10 m-long, 3 m-wide, and 0.5 m-deep) with slope gradient of 20° was subjected to three successive simulated rainfall events with intensities of 100 mm h^-1 for each experimental run. Two treatments (with and without cornstalk buffer strip) were tested in the following four runs to evaluate the timing effects of the buffer application: 1) without cornstalk buffer strip, 2) with cornstalk buffer strip in the third rain event, 3) with cornstalk buffer strip in the second rain event, 4) with continuous cornstalk buffer strip in all three successive rainfall events. In treatments with buffer, a 1 m-width cornstalk buffer strip was applied at the rill head before the prescribed rain. The results showed that, compared with the run without cornstalk buffer strip, the run with continuous cornstalk buffer strip in three successive rainfall events reduced soil loss by 29.1% while the other two runs with cornstalk buffer strips in a single event only reduced soil loss by 2.0% ~ 9.1%, and early buffer run had a larger reduction in soil erosion than late buffer run. The runoff-sediment relationship coefficients revealed a decrease in soil erosion by the buffer and an increase in the runoff threshold required to initiate soil loss. Moreover, the buffer strip increased sheet flow velocity in interrill areas, while it decreased concentrated flow velocity in rills. This promoted a shift of rill flow to subcritical laminar flow which reduced soil loss. Compared with non-buffer events, the critical shear stress increased from1.207 to 5.916 Pa, the critical unit stream power increased from 0.0291 to 0.0346 m s^-1, and the critical unit energy of cross section increased from 0.161 to 0.222 cm, respectively, in events with buffer.