Effects of ridge tillage and peanut growth on the surface–subsurface runoff generation and soil loss in the red soil sloping farmland of southern China

Proper tillage management and crop plantation are two established approaches to control soil erosion in red soil slopes of southern China. This study aims to investigate the surface–subsurface runoff and soil losses processes on sloping farmland under different peanut growth stages and ridge treatments, and to quantify the combined effects of proper tillage management and crop plantation.

Simulated rainfall experiments with an intensity of 60 mm h⁻¹ were conducted to measure the initiation time and steady rates of surface–subsurface runoff and soil losses under four tillage treatments including flat planting (FP), longitudinal ridge (LR), cross ridge (CR), and alternate distribution of cross and longitudinal ridges (CL) at the bare land and four different growth stages of peanut.

As peanut grew, the mean steady surface runoff rate for all treatments decreased by 19.6%, 38.8%, 54.0%, and 66.3% at the four growth stages respectively, and the mean steady subsurface runoff rate increased by 35.4%, 77.3%, 99.9%, and 118.4% at the four growth stages respectively. The maximum soil loss rate also decreased from 7.33 ~ 25.92 g m⁻² min⁻¹ at the seedling stage to 0.31 ~ 4.72 g m⁻² min⁻¹ at the full fruit stage. Compared with the FP treatment, the steady surface runoff rate for the LR treatment increased by 8.1 ~ 32.4% and the steady subsurface runoff rate reduced by 7.2 ~ 38.4%; while for the CR treatment, the steady surface runoff rate reduced by 77.6 ~ 92.7% and the steady subsurface runoff rate increased by 26.6 ~ 219.3%. As peanut grew, the contribution index of peanut to surface runoff increased from 0 at bare land stage to 0.80, 0.96, and 0.34 for the LR, CL, and CR treatment at the S4 stage, while the contribution index of ridge tillage to runoff generally decreased.

The inhibitory effects of peanut on surface runoff rate and sediment yield, as well as its promotion effect on subsurface runoff, were enhanced with peanut growth. Conversely, the impact of ridge tillage gradually decreased as peanut grew. On plots with longitudinal ridges, the impact of ridges on runoff was offset by contribution of crop growth after the seedling stage; whereas on plots with only contour ridges, the impact of ridges continued to dominate runoff control as peanut grew.