Changes in soil organic carbon stocks under 10-year conservation tillage on a Black soil in Northeast China

Biased assessment of tillage impacts on soil organic carbon (SOC) sequestration are often associated with a lack of information on the initial level of SOC stocks. The present study reported the changes in SOC concentrations and stocks following 10-year different tillage practices relative to the initial SOC levels. The tillage trial included no tillage (NT), ridge tillage (RT) and mouldboard plough (MP) on a Black soil (Hapludolls) in Northeast China. Results showed that tillage, soil depth and time significantly affected SOC concentration and SOC stock. Tillage and crop residue retention had great impacts on the SOC concentrations in the top 0.1 m layer. Compared with MP and NT, RT resulted in higher SOC concentration and SOC stock in the plough layer (0-0.2 m), which became more obvious with time. The soil under NT and RT had higher stratification ratios (SR) of SOC (SR, the ratio of SOC concentration in 0-0.05 m to that in 0.1-0.2 m) than under MP. Significant positive and nearly identical linear relationships between the SR of SOC and the duration of tillage practices occurred for both NT and RT soils; the increased SR in NT resulted from both SOC increase in surface and SOC decrease in subsurface soils, but in RT, the increased SR was only from a substantial SOC increase in surface soil. Accordingly, the present study highlights that RT was more helpful than NT in carbon sequestration for the studied Black soil in Northeast China.