Interplay of Crop Cover and Tillage on Runoff and Sediment Dynamics Under Simulated Rainfall: A Case Study in the Black Soil Region of Northeast China

We conducted 24 in situ simulated rainfall experiments featuring variable intensity over nine cropland plots subject to three tillage practices in the black soil region of Northeast China. The experimental setup involved eight scenarios, incorporating combinations of complete and zero crop cover, hourly rainfall amounts of 45 and 65 mm, and dry and wet antecedent soil moisture conditions. Our experiment shows that, compared to up and down the slope tillage (UDST) plots: (1) In the analysis aggregating multiple rainfall-runoff event data, contour tillage (CT) plots showed a notable increase in the reduction rates of total runoff, peak discharge and peak sediment concentration as crop cover increased from zero to complete. Specifically, reductions rose from 18%, 6% and 80% to 67%, 56% and 85%, respectively. In contrast, flat tillage (FT) plots showed a transition in total runoff and peak discharge from slightly more to slightly less, with a notable increase in peak sediment concentration reduction from 28% to 45% and (2) Analyses of individual events indicate that the ratio of total runoff, peak discharge and peak sediment concentration over CT plots compared to UDST plots range approximately in [6%, 100%], [6%, 100%] and [10%, 30%], these ratios over FT plots range in [60%, 130%], [60%, 130%] and [30%, 80%]. These data suggest that increased crop cover tends to amplify the total runoff and peak discharge reduction effects of tillage practices, and the runoff and sediment reduction rates vary notably across individual rainfall-runoff events. Additionally, both the magnitudes of amplification and variability depend on specific tillage practices employed. Notably, changes in crop cover have a more substantial impact on the runoff and sediment reduction effectiveness than variations in rainfall intensity and antecedent soil moisture. The necessity of employing in situ simulated rainfall experiments were also discussed. These findings highlight the interplay of crop cover and tillage on cropland runoff and sediment dynamics, offering valuable insights into improving soil and water conservation strategies.