Effect of Tillage and Residue Management on SOC and Response to Global Warming.

The North China Plain (NCP) is one of the most important agricultural regions in China. Crop residue is removed and used for heating and feed. A sustainable tillage-residue management system is needed in the NCP for soil health, productivity and a warmer environment. The objectives were to determine the effects of tillage-residue management systems for a winter wheat/summer maize double-crop system on soil organic carbon (SOC), CO₂ emissions, and the impacts of warming. No-tillage with residue cover (NTR), no-tillage with residue removed and manure applied (NTRRM), and conventional tillage with residue removed (CTRR) with uniform N application were investigated for 6 years. Subsequently, an open warming experiment was conducted by infrared heating of these long-term tillage-residue management plots to determine the effects of warming on crop growth stages and yield, soil SOC pools, and CO₂ emissions. NTRRM and NTR sequestered more SOC in the 0-5 cm depth than CTRR while the opposite was true in the subsoil. In the soil profile (0-60 cm), NTRRM, NTR and CTRR sequestered SOC at the rates of 0.66, 0.27 and 2.24 Mg ha^-1 yr^-1.  Warming increased soil temperature by 2.1°C and 1.5°C, and decreased volumetric soil-water by 14% and 10% for CT and NT systems, respectively. Winter wheat shortened its vegetative period to partly compensate for the negative effects of global warming. Soil CO₂ emissions tended to decrease with time in CT while it consistently increased in NT system under warming. The potential exist for warming to promote more soil CO₂emission under NT relative to CT. The activities of three extracellular enzymes, β-glucosidase, chitinase, and sulfatase, were higher under warming and no-till as compared to non-warmed and tilled soil. Predictions of C sequestration in the topsoil under no-till should be taken with caution, as this C pool is especially vulnerable to global warming.