Effects of grain-forage crop type and natural rainfall regime on sloped runoff and soil erosion in the Mollisols region of Northeast China

Clarifying the responses of runoff and soil erosion to crop type and rainfall regime is important for the optimization of crop planting systems and land use and management. This study was conducted to quantify the effects of five grain-forage crop types and rainfall regimes on sloped runoff generation and soil loss, and to further identify the factors influencing runoff and soil erosion in Mollisols region of Northeast China. Runoff and soil loss were monitored from 24 runoff plots including wheat, corn, soybean, alfalfa, and bromegrass, with the bare land as a control. 31 erosive rainfall events were classified into three rainfall regimes: regime Ⅰ with low precipitation (P) and duration (D), moderate intensity (I30) and frequent occurrence; regime Ⅱ with moderate P, long D and low I30; and regime III with high P and I30, moderate D and less frequent occurrence. Soil loss caused by regime III was 3.61–12.93 times greater than that under regimes Ⅰ and Ⅱ. Five crops reduced runoff and soil loss by 21.5%-69.3% and 54.1%-77.0%, respectively, of which bromegrass showed the highest reduction, especially the reductions of alfalfa and bromegrass under regime III, which were significantly higher than those of the three grain crops. Wheat showed a higher runoff reduction than soybean and corn but its soil loss reduction was lower due to harvest in mid-July. Crop type greatly influenced the correlations between runoff and soil erosion and rainfall and plant properties. Changes in runoff were significantly related to P, rainfall erosivity (EI30), coverage, plant height and root density, and the variations in soil erosion were dominated by runoff depth, D, EI30, and coverage. Path analysis showed that the rainfall and runoff properties produced larger influences on runoff depth and soil loss rate than plant traits. More attention should be paid to rainfall regime III, and grain and forage crops with shorter stems and higher coverage and earnings are preferred.