No tillage increases soil organic carbon storage and decreases carbon dioxide emission in the crop residue-returned farming system.

Soil organic carbon (SOC) storage and carbon dioxide (CO2) emission under different tillage methods in a crop residue-returned farming system may not be consistent with result from studies of the usual tillage researches because crop residues are important carbon sources with significant effects on soil carbon input and output. Herein, we address a knowledge gap over the "hot spot" research on tillage practices on SOC storage and CO2 emission in crop residue-returned farming systems. In this study, a long-term (2007-2019) field experiment was conducted, and the crop residues were returned to the soil after harvest; then, three tillage methods were conducted: no tillage (NT), subsoiling tillage (ST), and a moldboard plow tillage (CT). Our results showed that in the crop residue-returned farming system, NT and ST still showed advantages of lower CO2 flux compared with CT, as well as a reduced average CO2 flux of 14.5% and 8.5%, respectively, over a two-year average. The results of our long-term study suggest that the NT had advantages of SOC accumulation. In addition, as of June 2018, NT increased SOC stocks with 5.85 Mg hm-2 at a 0-60-cm soil depth compared with CT, whereas no significant difference was found between ST and CT. Overall, adopting NT in a crop residue-returned farming system improved SOC storage to 5.85 Mg hm-2 after 11 years as well as decreased CO2 flux by 14.5% in comparison with CT, which is meaningful in improving soil carbon pool and decreasing soil CO2 emission during agriculture production.