No tillage is not an ideal management for water erosion control in China

No tillage (NT) has been recommended as an essential conservation agriculture (CA) management in terms of water erosion control. However, the term of NT actually represents both NT and NT plus straw mulching (NTS) in a large amount of studies, which is out of the scope of its original meaning. Consequently, the mixed use of the two terms may cause biased estimate of the role of NT in erosion reduction. We aimed to distinguish actual roles of tillage reduction and residue retention in erosion control based on published data from field experiments of China. A database of paired experiments was compiled from 40 published literatures, with tillage practices including conventional tillage, reduced tillage, no tillage, and their combinations with residue retention. Variable-controlling approach was adopted to comprehensively identify the roles of tillage reduction and residue retention in runoff and soil loss reduction. Our results showed that residue retention caused significant decline of both water and sediment loss, whereas tillage reduction only led to insignificant change of runoff and soil loss. No tillage plus residue retention was also beneficial in terms of erosion control, very likely due to the application of residue retention. The results strengthen the higher influence of residue retention over tillage reduction with respect to soil and water conservation. It also challenges the conclusion of previous studies that NT could lead to the reduction of both runoff and soil loss based on the mixed use of NT and NTS. Furthermore, the efficiency of straw mulching in erosion control declines as application duration increases, indicating the effects of CA should not be overestimated in longer-term. The effectiveness of CA in erosion control also differs among various soil types. Overall, this study highlights the necessity of understanding the influences of tillage reduction, residue retention and the combination of the two managements in order to better evaluate and manage CA with respect to water erosion control, but the impacts of application duration of CA and soil types must be properly considered when adopting CA to reduce erosion.