LAUSR

ABSTRACT Soil total nitrogen (STN) and the carbon/nitrogen ratio (C/N) influence both crop production and microbial activity, but their distributions under different tillage practices are not clearly understood. This study investigated the effects of tillage practices on the vertical and temporal distributions of STN and the C/N ratio as well as on the distributions of STN fractions in a double rice cropping system from 2012 to 2017. Four tillage practices were established in 2005 in Southern China, i.e. no-till with rice straw mulch (NTS), rotary tillage with rice straw retention (RTS), plough tillage with rice straw retention (CTS), and with rice straw removal (CT). Even at 20–30 cm soil depth, long-term rice straw retention significantly increased STN and its fractions compared to those for CT. Noticeably, at 0–5 cm soil depth, the C/N ratio under NTS was 1.6–6.5% lower than those of other treatments, with a larger amount of rice straw input. In addition, long-term rice straw retention (NTS, RTS, and CTS) increased rice yield by 6.2–14.2% compared to that for CT. Therefore, long-term rice straw retention is recommended in this region due to its ability to increase N accumulation (even at deeper soil depths), which might improve the rice production.