Soil erosion processes on row sideslopes within contour ridging systems

- Runoff and erosion were strongly affected by ridge width and ridge height.
- Interactions of ridge topography, row grade, and rainfall intensity are important.
- Reducing field slope and using high ridges may decrease the risk of contour failure.

Soil erosion from row sideslopes can result in contour failure and reduce the soil conservation capacity of contour ridges. Understanding soil erosion processes on row sideslopes and their effects will improve our understanding of soil erosion in contour ridge systems. This knowledge will provide guidance for improving the use of contour ridges. In this study, 32 rainfall simulation experiments were conducted in order to analyze the effects of two different microtopography indices (row grade and field slope), two ridge geometry indices (ridge height and ridge width), and rainfall intensity on erosion of sandy brown soil with two replications.Based on the runoff and sediment yield time series, which was monitored over 1 min intervals, the soil erosion process was classified into periods of interrill or rill erosion. The runoff values for the two periods accounted for approximately 44.2% and 55.8% of the entire runoff value, respectively. Sediment was mainly generated from rill erosion (87.2%). However, interrill erosion occurred most of the time (72.3%). During the interrill erosion period, the ridge width and rainfall intensity significantly and positively affected the amount of runoff (contributions of 33.1 and 28.7%, respectively) and sediment yield per min (14.8 and 17.0%, respectively). Ridge height significantly and positively affected the runoff per min but not the sediment yield per min. In contrast, field slope negatively affected runoff per min, which indicated that the runoff during the interrill period was mainly affected by the ridge geometry, while the sediment yield per min was mainly affected by the microtopography relief. During the rill erosion period, the ridge height significantly and negatively affected the runoff per min because the increasing ridge height prolonged the duration of this period and enhanced infiltration, and the row grade significantly and positively affected the sediment yield per min, which resulted from decreasing soil cohesiveness with increasing row grade. The entire runoff and sediment yield per min during the experiment were influenced by the same factors that influenced the interrill and rill erosion periods, respectively. Interactions between the different factors, especially between ridge height, row grade, and rainfall intensity, play an important role during the erosion process by increasing runoff and sediment yield per min. Therefore, reducing the field slope and using high ridges may reduce contour failure during rainfall events.