Partial substitution of biogas slurry for chemical fertilizer increased wheat grain yield while alleviating N2O emissions by improving soil quality and regulating N cycling genes

Overuse of chemical fertilizers (CF) degrades soil and environmental quality.Replacing chemical fertilizer (CF) with biogas slurry (BS), an organic alternative, offers a sustainable solution. However, the mechanisms by which BS balances yield benefits with N2O emissions, along with metagenomic insights, remain unclear. This study examined six fertigation strategies including control, 100%CF, and 25%, 50%, 75%, and 100% BS substitution for CF, on soil quality index (SQI), nitrogen use efficiency (NUE), wheat growth and nutrient uptake, grain yield, and N2O emissions, along with metagenomic analysis. The results showedthat 50% BS substitution significantly (p < 0.001) increased wheat tillers (43.5%), dry matter (21.6%), N uptake (52.6%), NUE (32.2%), and grain yield (24.4%) compared to 100%CF. Furthermore, it also reduced N2O emissions by 26.9% and yield-scaled N2O emissions by 44.8%. The structural equation modeling (SEM) demonstrated that the enhanced SQI (57.8%) significantly boosted grain yield and NUE, which was ascribed to the N2O emission reduction. The 50%BS treatment significantly reduced archaeal ammonia monooxygenase (ArchamoA) abundance compared to 100%CF, with metagenomic analysis revealing that N2O emissions were mainly attributed to Arch-amoA. SEM analysis confirmed that N2O emissions were mainly driven by Arch-amoA over the bacterial ammonia monooxygenase (Bac-amoA) in nitrification and nosZ over nirS in denitrification, significantly reducing emissions. Random Forest analysis identified that available N (NH4+-N and NO3--N) dominantly moderate grain yield, while soil pH, C:N, available N, and total N importantly regulate N2O emissions. Replacing 50% CF with BS in wheat sustainably enhances yield, reduces N2O emissions, and promotes environmental sustainability. • 50% BS substitution for CF improved wheat N uptake (52.6%), NUE (32.2%), and soil quality (57.8%) • The improved soil quality boosted NUE, yield (24.4%) and cut N 2 O emissions (26.9%) • Metagenomic analysis revealed that amoA primarily drove N 2 O emissions in this study • 50% BS substitution reduced amoA while enhanced nosZ , resulting in lower N 2 O emissions • Soil pH regulated N₂O emissions, whereas available N importantly determine wheat grain yield