Effects of ditch-buried straw return on soil organic carbon and rice yields in a rice–wheat rotation system

•Ditch-buried straw returning is a novel returning method.•Ditch-buried straw returning significantly increased SOC.•Abrupt rise of SOC occurred in the 10 cm-soil layers above and below straw layers.•Straw returning with full amounts to 20 cm showed higher carbon sequestration potentials and rice yields.

A novel straw return method (ditch-buried straw return, DB-SR) with a four-year field experiment was implemented to investigate the carbon sequestration effect under various burial depths and with different amounts in a rice–wheat rotation system. The DB-SR significantly increased the soil total organic carbon (TOC) and labile organic carbon (LOC) contents. In the two soil layers 10 cm above and below the straw layer, the TOC and LOC levels increased. The DB-SR treatment using the total amount of straw showed higher TOC, LOC and carbon pool management index (CPMI) values than when half and twice the amount of straw were used. The rice yield was significantly higher when the total amount was used with the DB-SR to depth of 20 cm than at other soil depth treatments. However, the DB-SR with twice the amount showed a negative, but not significant, effect on rice yields. These results suggest that DB-SR might be a better straw return method to increase soil organic carbon (SOC) and improve soil quality, particularly when returning the total amount of straw to a soil depth of 20 cm.