Long-term ditch-buried straw return alters soil carbon sequestration, nitrogen availability and grain production in a rice–wheat rotation system

Our previous studies indicated that ditch-buried straw return (DB-SR) can improve soil processes in the short term, i.e. increasing microbial metabolic capability, reducing nitrogen leaching loss and promoting soil aggregation. However, it remains unclear how long-term implementation of DB-SR affects soil carbon (C) and nitrogen (N) processes and crop yields. Here, the effects of DB-SR on soil C pool and N availability as well as grain yields were investigated after consecutive application of 6 (rice season) and 6.5 years (wheat season). We found that long-term DB-SR significantly increased rice yields, total organic C, NH4+ and NO3– in the rice soils, as well as enhanced wheat yields, microbial biomass C, microbial biomass N, microbial biomass C/total organic C ratio and microbial biomass C/N ratio, but reduced NH4+ and NO3– in the wheat soils when compared with rotary tillage straw return (RT-SR) and no tillage with straw removal (NT-NS). These findings suggest that long-term DB-SR application has positive effects on grain production, but possibly through different mechanisms in improving soil processes. The yield-increasing effects on rice might result from improvements in soil fertility, whereas increased wheat yields can be ascribed to stimulated soil microbial activity.