Tillage impacts on net carbon flux in paddy soil of the Southern China

Scientific regulation of carbon (C) flows under conservation tillage is of great significance for mitigating C emission to the atmosphere and increasing C sequestration potential in soils. The objective of this study was to assess tillage impacts on C cycle from a situ field experiment and identify potential tillage practices for C-smart technology in paddy soils of the Southern China. A field experiment was conducted during 2005-2011, including conventional tillage without residue retention (CT), conventional tillage with residue retention (CTS), rotary tillage with residue retention (RTS), and no-till with residue retention (NTS). We computed SOC concentrations, SOC stocks and C emissions from farm inputs with time, and results in values representing a change in net carbon flux under different tillage systems in a double rice (Oryza sativa L.) cropping system. The annual increase rates of SOC stocks were 452.6, 523.3, 1340.8, and 2385.4 kg ha−1 yr−1 from 2007 to 2011 under CT, CTS, RTS, and NTS, respectively. The annual C emissions under CT, CTS, RTS, and NTS were 1182.5, 1182.5, 1152.5, and 1139.2 kg C-eq ha−1 yr−1, respectively. Among the treatments, NTS treatment had the lowest net C flux with −1246.2 kg C-eq ha−1 yr−1. Taking CT as the baseline, the relative net C flux under RTS and NTS were −918.2 and −1976.1 kg C-eq ha−1 yr−1, respectively. This suggests that adoption of conservation tillage would be beneficial in the reduction of GHG emission and could be a good option for C-smart agriculture in double rice cropping regions.