Increasing soil organic matter and nitrogen use by optimizing summer maize straw return and nitrogen fertilizer rates minimize N2O emissions in a wheat–maize system

Straw with N increased yield by regulating soil quality and post-flowering N accumulation. 2. Moderate reductions in the amount of straw or N applied will not result in reduced soil quality and crop yields. 3. Straw and N fertilizers affect N 2 O emissions by influencing the abundance of bacteria involved in aerobic ammonia oxidation and nitrate respiration. Effects of maize straw return and N fertilizer application on soil quality and crop yield have been extensively researched. However, the effects of different amounts of maize straw returned to the field with different nitrogen application rates on the soil-crop system quality, abundance of functional N cycle microorganisms, N 2 O emissions and crop N nutrition status of crops remain incompletely explored. Objective of this study was to assess the effects of different summer maize straw return rates and N application rates on: i) soil quality and crop productivity; ii) the community of N cycle-functional microorganisms and N 2 O emission, and iii) crop N status. Results indicated that crop yields increased by 7.62 to 12.69% at 210 kg ha -1 of N application for full straw return (SN) and half return (1/2SN) compared to the no-return treatment (CK). No significant difference was recorded in yield between the full straw return reduced by 15% (178.5 kg N ha -1 ) of N fertilizer (S-15%N) and SN. Surface soil layer (0-20 cm) showed significantly higher levels of soil organic matter (SOM), the community of N-cycling functional microorganisms, crop N nutrition status and N uptake efficiency in SN, 1/2SN, and S-15%N as compared to other treatments. S-15%N and 1/2SN reduced cumulative N 2 O emission fluxes by 19.11 and 5.51%, respectively, compared to SN. Furthermore, the nitrogen nutrient index (NNI) of 1/2SN, S-15%N was closer to the critical N requirement than SN. In summary, the decision schemes for optimal straw return and N application (1/2SN and S-15%N) based on SOM, NNI, cumulative N 2 O emission fluxes and yield can be applied to the annual production of winter wheat and summer maize in China as compared to SN.