Effect of rainfall intensity and duration on soil erosion on slopes with different microrelief patterns

Tillage-induced surface microrelief (TSM) is commonly thought of as an effective measure to control soil erosion on agricultural lands. The objective of this study is to discuss how rainfall intensity and duration affect the role of TSM in soil erosion. Three rainfall intensities of 60, 90 and 120 mm/h and four rainfall durations of 15, 30, 60 and 90 min for each intensity were investigated. Two slope ranges, corresponding to a gentle slope (5 degrees to 10 degrees) and a steep slope (20 degrees to 25 degrees), were considered. Two different TSMs, consisting of depressions and mounds (DM) and troughs and ridges (TR), were used for testing in a soil box that was 2 m long by 1 m wide. A smooth surface (SS) served as a control. The runoff and sediment reduction benefits (RRB and SRB), represented by the ratios of the difference between the tilled slope and SS to that of SS, were used to quantify the role of TSM in soil erosion. The results showed that DM and TR delayed runoff initiation regardless of rainfall intensity and slope. The TSM RRB and SRB decreased with increasing rainfall intensity, duration and slope. Compared to the SS, the DM RRB decreased from 43% to 6% when the rainfall duration increased from 15 to 90 min, and the TR RRB decreased from 100% to 31% on the gentle slopes; on the steep slopes, the DM and TR RRBs decreased from 24% and 46% to nearly zero when the rainfall duration increased from 15 to 90 min. When rainfall intensity was below 90 mm/ h and the duration was shorter than 60 min, DM and TR were effective at controlling soil loss; when the duration increased to 90 min or the rainfall intensity was 120 mm/h, the sediment form DM and TR was much higher than that from SS. In particular, the sediment from DM and TR increased by 114% to 330% when the rainfall intensity was 120 mm/h. This indicates that DM and TR were not effective at controlling soil loss during rainfall with a high rainfall intensity and/or long duration. In addition, TR exhibited greater effectiveness at controlling soil and water loss than DM under the same situations. Therefore, rainfall conditions and slopes are important factors influencing the soil and water conservation benefits of TSMs, and the effectiveness of TSMs on soil erosion reduction needs to be further assessed in conjunction with climate change.