Effects of partial substitution of chemical fertilizer with biogas slurry on nitrous oxide emissions and the related nitrifier and denitrifier in a saline–alkali soil

Abstract

Returning to cropland of the biogas slurry (BS) from mixed anaerobic fermentation of distiller’s grain and pig manure may hold the notable potential to reduce N 2 O emissions and enhance soil biological activity. However, the mechanism driven by nitrifier and denitrifier remains unclear. Here we conducted a pot experiment with biogas slurry substitution for chemical fertilizer (CF) to investigate the combined impacts of BS and CF on N 2 O emissions and nitrifier and denitrifier communities. Four treatments were established: CK (no BS application); T1 (158 kg N ha −1 from BS); T3 (126 kg N ha −1 from BS); T6 (79 kg N ha −1 from BS). This study showed that cumulative N 2 O emissions were significantly reduced by 54.0%–36.0% in BS compared to the only chemical fertilizer application ( p < 0.05). Biogas slurry partially substituted for CF decreased the AOB- amoA , nirK and nirS copies by 28.4–74.4%. The lower AOB- amoA and nirS may be the key factors for lower N 2 O emissions in BS treatments. Soil NO 3 − N and C/N were the most important soil properties affecting N 2 O emission analyzed by random forest analysis. The application of BS also weakened the soil salt stress in N cycling processes as the Shannon of nirS and nosZ type denitrifiers increased with the reduction of SSC ( p < 0.05). These findings provided novel insights into how biogas slurry reduces N 2 O emissions and modulates its pathways in saline–alkali soil. Biogas slurry partially substituted for chemical fertilizers will be a reasonable practice to return biogas slurry to the field. • Biogas slurry partially substituted the chemical fertilizers decreased N 2 O emissions. • The AOB- amoA and nirS were key genes for lower N 2 O emissions. • Soil C/N and NO 3 - -N were the main environmental factor affecting N 2 O emissions. • Biogas slurry weakened the stress pressure of soil salt on N cycling processes.