How does straw returning combined with nitrogen fertilizer drive N₂O emission in wheat-maize rotation system

Straw returning not only improves carbon (C) and nitrogen (N) pools but also increases soil nitrous oxide (N2O) emissions, which poses a threat to the sustainable development of agriculture. To investigate the effect of straw return combined with nitrogen fertilizer on labile C and N pools in the soil and short-term response to soil N2O emissions in wheat-maize rotation system. The consecutive field experiment was conducted from 2019 to 2021. Single factor randomized block design was used in the experiment design, with no straw returning and no fertilizer (CK), no straw returning and nitrogen fertilizer (S0N) and straw returning combined with nitrogen fertilizer (SN). The results indicated that the SN and S0N treatments significantly (p < .05) increased N2O emissions by 170.45% (2.43 kg N ha(-1) year(-1)) and 119.5% (1.70 kg N ha(-1) year(-1)), soil organic carbon (SOC) by 17.23% and 14.50% and soil total nitrogen (STN) by 58.50% and 31.50% respectively. In the 2020-2021 growing season, The soil microbial biomass carbon (SMBC) content of the SN and S0N treatments were higher than those of CK in the winter wheat seedling, winter wheat jointing, winter wheat booting, summer maize seedling and summer maize bell-mouth stages. The structural equation model (SEM) indicated that C:N and NO3--N were the major drivers that increased soil N2O emissions, but SMBN was the main driver that decreased soil N2O emissions. The SN and S0N treatments significantly increased soil N2O emissions by increasing the NO3--N content. However, compared with the CK and S0N treatments, the SN treatment mitigated soil N2O emissions by increasing the SMBN content. More importantly, compared with CK treatment, SN treatment increased annual yield by 48.41% and 34.52%, the SN treatment could effectively improve the soil C and N pools. Therefore, straw return combined with nitrogen fertilizer (SN) may be the best choice of the treatments tested for reducing greenhouse gas emissions and achieving green and sustainable development.