Identifying optimal ridge practices under different rainfall types on runoff and soil loss from sloping farmland in a humid subtropical region of Southern China

The relationship between different rainfall types, different soil management practices, and soil erosion is not yet fully understood. In-situ observations of soil and water loss on sloping farmland in the red soil region of southern China with a subtropical monsoon environment were taken at 12 runoff plots with four treatments, i.e, downslope ridges, downslope ridges with hedgerow intercropping, contour ridges, and bare flat land as control, over a seven-year period from 2012 to 2018. During this time, 253 natural rainfall events were classified into three rainfall types by K-means clustering according to the rainfall depth, maximum-30 min rainfall intensity and rainfall duration, and surface runoff and soil erosion processes in relation to the rainfall types under different ridge practices were analyzed. The results show that water-induced soil erosion on the flat land control was significant, with average annual soil loss of 76.73 t.ha(-1).yr(-1), reaching the intense erosion classification, and ridge practices were confirmed to reduce annual runoff and soil loss in all rainfall events by 18.9-62.0% and 68.9-86.3%, respectively. On the whole, rainfall events can be divided into three types: intense, normal, and long-duration. Among them, intense and normal rainfall cause the majority of soil (88.5-93.7%) and water (75.0-83.8%) loss in this area, but the efficiencies in runoff and soil reduction during long-duration rainfall events were the lowest, or even negative on farmlands with only downslope ridges. 20% of the total rainfall events, in which 84.3-92.2% were intense and normal rainfall events, contributed to 29-33% of the total rainfall depth, 68-89% of the total runoff depth, and 94-98% of the total soil loss. Rainfall depth played a dominant role in generating runoff, while runoff accumulation was a main factor influencing on soil loss. Findings from our study indicate that by choosing a more appropriate ridge practice according to different rainfall types, there can be a positive effect on soil and water conservation.

Automated summary

The relationship between different rainfall types and soil erosion is complex, yet ridge practices have been shown to reduce runoff and soil loss in intense and normal rainfall events. Choosing appropriate ridge practices according to rainfall types can have a positive impact on soil and water conservation, with more significant effects observed during intense and normal rainfall events.