Effects of crop growth and surface microtopography on runoff and soil losses in the red soil region of southern China

Surface conditions such as vegetation cover and microtopography are main determinants of soil erosion, while their hydrological functions are not fully understood on tilled slopes. In this study, in-situ observations were carried out during four growth stages of peanut (seedling, needling, podding, and full fruiting stages) from 2021 to 2022 in Jiangxi Province on red soil slopes using three tillage practices, including flat planting (FP), flat planting with hedgerow intercropping (HG) and longitudinal ridge (LR), with bare land as the control (CK). The surface runoff and sediment yields were measured on runoff plots under 29 natural rainfall events during peanut growing season of 2021-2022. The digital elevation model (DEM) under different tillage practices, and vegetation cover maps at different growth stages were derived based on unmanned aerial vehicle photogrammetry, which were used to calculate microtopography parameters and hydrological connectivity indices (e.g., surface roughness, topographic wetness index, and Leakiness Index). Results showed that the total runoff yields for HG, FP, and LR plots were significantly reduced by 92.5 %, 85.8 %, and 56.8 % respectively compared with CK during the peanut growing season, and sediment yields were reduced by over 95.0 %. The crop cover reduced the runoff yield by 41.9 %, 86.2 %, 94.6 %, and 97.0 % at the seedling, needling, podding, and full fruiting stage respectively compared to CK, and reduced the sediment yield by above 95.0 % at each growth stage. The hydrological connectivity indices Flowlength (Flen) and Leakiness Index (LI) well represented the runoff transport capacity of sloping land and can be used to quantitatively assess the effects of microtopography and crop growth. This study provides further understanding of microtopography and vegetation cover patterns on soil erosion by using hydrological connectivity indices.