Effects of tillage systems on soil organic carbon and total nitrogen in a double paddy cropping system in Southern China

• We assessed tillage effects on SOC and TN stocks in a double rice cropping systems.
• Tillage intensity affected the SOC and TN concentrations and their SR.
• Small difference in soil C:N ratio was observed among treatments.
• Crop residue returning is critical to SOC, TN and soil quality improvement.
• Rotational tillage may be an appropriate farming practice for paddy rice system.

Soil organic carbon (SOC) and total nitrogen (TN) stocks in cropland soils play important roles in soil quality and climate change mitigation. Farming management have great impacts on SOC and TN dynamics, and thus affecting soil quality. The objective of this study was to assess the effect of tillage systems on the changes in SOC and TN pools under a double rice (Oryza sativa L.) cropping system in Southern China. A field experiment was conducted during 2005 in Ningxiang, Hunan Province. It comprised of four tillage treatments including no-till with residue retention (NT), rotary tillage with residue incorporation (RT), plow tillage with residue incorporation (PT), and plow tillage with residue removed (PT0). The results showed that NT increased soil bulk density (ρb) in the 0–20 cm soil layer. Adoption of NT increased the concentrations of SOC and TN at 0–5 cm depth but decreased the concentrations in deeper soil. The greatest SOC and TN concentrations were observed under RT at 5–10 cm depth and under PT at 10–20 cm depth. Tillage practice had small effect on the soil C:N ratio in the soil profile. Adoption of NT farming enhanced the SOC and TN stocks in the 0–10 cm layer, whereas PT increased SOC and TN stocks in the 0–50 cm profile. The stratification ratio (SR) of the SOC and TN concentrations were larger under NT compared with RT and PT. Thus, the adoption of short-term (7–8 years) NT practices is beneficial for the enhancement of SOC and TN stocks in the 0–10 cm soil profile, and rotational tillage may be an appropriate farming practice for paddy rice system.