For smooth and wide application of conservation agriculture (CA), remaining uncertainties about its impacts on crop yield need to be reduced. Based on previous field experiments in China, a meta-analysis was performed to quantify the actual impacts of CA practices (NT: no/reduced-tillage only, CTSR: conventional tillage with straw retention, NTSR: NT with straw retention) on crop yields as compared to conventional tillage without straw retention (CT). Although CA practices increased crop yield by 4.6% on average, there were large variations in their impacts. For each CA practice, CTSR and NTSR significantly increased crop yield by 4.9% and 6.3%, respectively, compared to CT. However, no significant effect was found for NT. Among ecological areas, significant positive effects of CA practices were found in areas with an annual precipitation below 600 mm. Similar effects were found in areas with annual mean air temperature above 5 °C. For cropping regions, CA increased crop yield by 6.4% and 5.5% compared to CT in Northwest and South China, respectively, whereas no significant effects were found in the North China and Northeast China regions. Among crops, the positive effects of CA practices were significantly higher in maize (7.5%) and rice (4.1%) than in wheat (2.9%). NT likely decreased wheat yield. Our results indicate that there are great differences in the impacts of CA practices on crop yield, owing to regional variation in climate and crop types. CA will most likely increase maize yield but reduce wheat yield. It is strongly recommended to apply CA with crop straw retention in maize cropping areas and seasons with a warm and dry climate pattern.
