Does straw return increase crop yield in the wheat-maize cropping system in China? A meta-analysis

Straw return into agricultural soil is one of the most important management practices in China. However, the direction and magnitude of crop yield to straw return are inconsistent from individual studies in wheat-maize cropping systems of Chinese upland soils. Hence, we conducted a meta-analysis of 1071 comparisons from 177 peer-reviewed publications to evaluate the effect of straw return on the yield in the wheat-maize cropping system varied with climate conditions, management practices, and soil properties. Overall, crop yield response to straw return in the mono-cropping system (11.8%) is significantly greater than that in the double-cropping system (5.5%). The positive effect is obvious in regions with subtropical climates (> 15 °C annual temperature and > 800 mm annual precipitation). Without fertilizer application, straw return has no improvement on crop yield in the mono-cropping system, or even decreases crop yield by 2.42% in the double-cropping system, while it will yield more under N fertilizer application of 150–200 kg ha−1 yr−1 for mono (16.4%) and > 300 kg ha−1 yr−1 for double (6.99%) cropping system. For both cropping systems, yield increase peaked at around 10–15 years. The positive effect of straw return on crop yield is more obvious under the conditions with irrigation, and deep tillage. For straw return method, straw incorporation presents a greater effect than straw mulching does. The increase in crop yield after straw return is closely related to the improvement of soil organic carbon, soil structure and nutrients. Therefore, our results indicate that straw incorporation under the conditions with deep tillage, irrigation and fertilization, has great potential to increase crop yield in the wheat-maize cropping system.