Stover retention rather than no-till decreases the global warming potential of rainfed continuous maize cropland

During the past two decades, conservation management practices to sequester soil carbon have been recommended to mitigate greenhouse gas (GHG) emissions. However, the long-term effects of no-till, stover retention, and their interaction on soil organic carbon (SOC) stocks and GHG emissions from rainfed croplands remain uncertain. In this study, tillage practice and stover management effects were investigated in a long-term rainfed continuous maize cropping system. Measurements of soil nitrous oxide (N2O) and methane (CH4) fluxes and SOC change were conducted in four treatments: conventional tillage with stover removal (CT), conventional tillage with stover retention (CS), no tillage with stover removal (NT) and no tillage with stover retention (NS). Annual N2O emissions with stover retention (CS and NS, 0.52-0.74 kg N ha(-1) yr(-1)) were significantly higher (P < 0.0001) than those with stover removal (CT and NT, 0.40-0.55 kg N ha(-1) yr(-1)), but N2O emissions were not affected by tillage practice. Net CH4 consumption occurred in all treatments, but no significant effect of tillage practice or stover management was found. Surface (0-20 cm) SOC stocks decreased with both stover removal and no tillage practice, while deep SOC (20-100 cm) was not affected by tillage practice or stover management over ten years. Stover retention led to a net GHG sink with annual global warming potential (GWP) values of -2.52 +/- 0.05 and -1.03 +/- 0.02 Mg CO2-eq. ha(-1) yr(-1) for CS and NS, respectively, but stover removal practices were a net GHG source with annual GWP values of 0.83 +/- 0.04 and 1.40 +/- 0.04 Mg CO(2)eq. ha(-1) yr(-1) for CT and NT, respectively. Our results highlight the importance of C input from crop residues for increasing SOC stocks and mitigating GHG emissions. Therefore, conventional tillage with crop residue return is the most promising management system for simultaneously achieving maximum yield and minimum GWP.