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

Abstract

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 fertiliser 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 fertiliser (CK), no straw returning and nitrogen fertiliser (S₀N), and straw returning combined with nitrogen fertilizer (SN). The results indicated that the SN and S₀N treatments significantly (P < 0.05) increased N₂O emissions by 170.45% (2.43 kg N ha^-1 yr^-1) and 119.5% (1.70 kg N ha^-1 yr^-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 fertiliser (SN) may be the best choice of the treatments tested for reducing greenhouse gas emissions and achieving green and sustainable development.