Mechanisms and benefits of straw return in mitigating black soil erosion

Soil erosion is a serious problem in the black soil region of Northeast China leading to severe land degradation, which directly threatens both regional ecological security and national food security.Straw return is a conservational tillage measure widely applied in this region and plays an important role in mitigating soil erosion, preventing land degradation and promoting ecological and production functions of degraded black soils.In the current study, the mechanisms of straw return in mitigating interrill, rill, ephemeral gully and gully erosion were systematically analyzed, and its soil and water conservation benefits were comprehensively evaluated.The key topics for future research were proposed.The mechanisms of straw return in mitigating soil erosion are directly related to erosion type.Regarding interrill and rill erosion, the direct effects of straw mulching include alleviating raindrop kinetic energy, inhibiting soil physical crust formation, maintaining soil infiltration capacity, increasing land surface random roughness, and decreasing flow velocity, as well as sediment transport capacity and flow shear stress.The indirect effects primarily originate from straw decomposition, which includes improving soil physical and chemical properties, enhancing aggregate formation and increasing its stability, and changing crop growth characteristics.Consequently, both interrill and rill erodibilities are decreased, and the soil critical shear stress is increased.The effects of straw return on restraining ephemeral gully and gully development are not direct as that of interrill and rill erosion.Nevertheless, straw return can reduce the risk of such erosion by decreasing the erosive power of flow via reducing their drainage area.Straw return exhibits significant soil and water conservation benefits, which decreases runoff and soil losses by 28.0%-95.1% and 40.3%-99.7%, respectively.Owing to the different experimental designs, however, hardly can the corresponding results be compared directly.To alleviate soil degradation, maintain regional ecological security and ensure national food security, future research should emphasize on the hydraulic mechanisms of straw return in increasing land surface random roughness and flow friction, as well as in decreasing flow sediment transport capacity; the responses of soil erodibility to soil physical and chemical properties changes resulting from straw return; the soil and water conservation benefits of straw return among different soil types and slopes, and the controlling factors; the long-term effects of straw return in reducing soil erosion and their spatial variation; and the impacts of straw return technique on soil erosion processes and the related mechanisms.