Extension of residue retention increases net greenhouse gas mitigation in China's croplands

Crop residue retention plays an important role in greenhouse gas (GHG) mitigation for global agriculture. To clarify the current status of residue retention and burning as well as the contribution of these processes to GHG dynamics, we conducted a nationwide survey on residue management in China in 2011 and improved the Carbon Accounting and Net Mitigation of Straw return model with updated parameters. The results indicated that residue retention increased from 144 Mt yr−1 in 2001 to 295 Mt yr−1 in 2011, whereas burned residue reached 200 Mt yr−1 in China. Because of these increases in residue retention, the net mitigation related to residue retention increased from 5.3 Tg Ce in 2001 to 13.3 Tg Ce in 2011. Further extension would sequester 15.8 Tg C, which is equivalent to a reduction in emissions of 3.9 Tg Ce from residue burning and a mitigate potential of 3.1 Tg Ce from replacing 1.5 Mt of nitrogen fertilizer. However, the national net mitigation from residue retention would achieve only 45-64% of the total soil C sequestration. The spatial heterogeneity of cropping systems and residue management was determined to have different effects on GHG dynamics. The net mitigation would have a negative value in eight provinces because of incremental increases in methane emissions from rice paddies. Increases in residue retention in the remaining 23 provinces would result in a maximum mitigation potential of 10 Tg Ce yr−1 and offset the carbon dioxide emissions caused by fossil fuel burning by 0.5% from the national value in 2011. Therefore, residue retention has mitigated a substantial amount of GHGs, and extending this strategy has considerable mitigation potential for China's croplands. Our results indicate that the retention and burning of crop residues have an effect on the GHG dynamics in China and represent potential strategies for mitigating climate change via residue management.