The Responses of Soil N2O Emissions to Residue Returning Systems: A Meta-Analysis

Background: Much attention has been focused on the influences of residue returning on N2O emissions. However, comprehensive quantification of the effect size on N2O emission following crop residue returning in subtropical, tropical and warm temperate conditions remains untested. Methods: To identify site-specific factors that influence N2O emission (kg N2O-N ha(-1)) in residue returning systems, we performed a meta-analysis involving 260 comparisons from 72 studies. Results: The data indicated that significant promoting effects were observed under residue returning by rotary tillage, no-tillage and mulch, whereas N2O release was significantly inhibited by 8% under residue returning by plough. For other contributors, the stimulatory and significant effects occurred in upland fields, under short- and medium-term residue returning durations, acidic/neutral soils, medium organic C and clay content. Nitrogen fertilizer application significantly stimulated N2O emission, even though application rate at 100-150 kg N ha(-1) was inhibitory. Although a negative correlation between residue C/N ratio and N2O emission has been shown, residue returning could not reduce N2O emission with a higher C/N ratio and amount. Conclusions: Some options, such as converting residue returning methods, decreasing N fertilizer application rate, and regulating soil C/N ratio could be adopted to mitigate soil N2O emission following residue returning.