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

Abstract

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 showed that 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 (Arch-amoA) 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 moderated grain yield, while soil pH, C:N, available N, and total N importantly regulated N₂O emissions. Replacing 50 % CF with BS in wheat sustainably enhances yield, reduces N₂O emissions, and promotes environmental sustainability.