Stover retention rather than no-till decreases the global warming potential of rainfed continuous maize cropland
Citation
Fan, J., Luo, R., Liu, D., Chen, Z., Luo, J., Boland, N., Tang, J., Hao, M., McConkey, B., Ding, W. (2018). Stover retention rather than no-till decreases the global warming potential of rainfed continuous maize cropland. Field Crops Research, [online] 219 14-23. http://dx.doi.org/10.1016/j.fcr.2018.01.023
Plain language summary
Practices that increase soil organic carbon remove carbon dioxide from the atmosphere. These practices then can counteract climate change caused by buildup of greenhouse gases in the atmosphere. For this reason, over the last 20 years, there have been recommendations to adopt farming practices to increase soil organic carbon. Tillage and removal of crop residues from the field are practices that affected soil organic carbon. This study conducted in east-central China evaluated the effects of no-till versus plowing, with and without leaving corn stover (stover = above-ground corn residue) in the field, on soil organic carbon storage and on emissions of greenhouse gases. Over a 10-year period, the soil organic carbon in the upper 20 cm of soil was lower when corn stover was removed. Soil organic carbon also tended to be lower with no-till than plowing. The soil organic carbon below 20 cm soil depth was unaffected by the production practices. The emission of the greenhouse gas, nitrous oxide, was lower when corn stover was removed. The soil took up small amounts of the greenhouse gas, methane, from the atmosphere about equally for all practices. The corn grain yield was highest for plowing with corn stover left in the field and lowest for plowing with corn stover removed from the field. In terms of net total greenhouse gas emissions, the best treatment was plowing with corn stover left on the field. This combined practice had an annual net removal of greenhouse gases equivalent to 2.5 tonnes of carbon dioxide per hectare. The worst net greenhouse gas emission was for the practice of no-till with corn stover removed. It had an annual net greenhouse gas emission equivalent to 1.4 tonnes of carbon dioxide per hectare. Plowing with corn stover left on the field was the optimum practice because it had the highest yield and the greatest net removal of greenhouse gases from the atmosphere.
Abstract
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 CO2-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.