How does straw-incorporation rate reduce runoff and erosion on sloping cropland of black soil region?

Straw-incorporation has been widely utilized as an important practice for agricultural soil carbon sequestration, but few studies have been performed to investigate its impact on cropland runoff and erosion. In this study, the relationships between straw-incorporation rate and cropland runoff and erosion were quantified through field observations in the black soil region of Northeast China. Runoff and erosion were significantly influenced by straw-incorporation rate. Compared to the treatment without straw-incorporation, the mean runoff depth and soil erosion rate of seven observed rainfall events reduced by - 0.04-0.72 mm and - 3.34-15.34 t km-2. Under different straw-incorporation rates, the runoff reduction percentage (RRP) and erosion reduction percentage (ERP) varied from 7.3% to 90.3% and - 4.2-92.5%, with the means of 62.5% and 61.4%. RRP was mainly attributed to plant coverage, root mass density and the maximum 30-minute rainfall intensity, while plant coverage, leaf area index and the maximum rainfall intensity of ten minute were identified as the main factors influencing ERP. These parameters could explain 47%, 6%, 47% and 45%, 44%, 11% of total variations of soil erosion and runoff, respectively. Overall, straw-incorporation was effective in mitigating runoff and erosion under non-extreme rainfall event when straw-incorporation rate was greater than 4.5 t hm-2. Strawincorporation rate of 9 t hm-2 had the best benefits to control runoff and erosion, followed by 13.5 t hm-2, while 1.125 t hm-2 had the least benefits. Our results highlight an importance of straw-incorporation in reducing cropland runoff and erosion and the implication for controlling soil erosion and associated environment problems by selecting best crop straw managements in semi-humid region of the world.