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 N2O 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 N2O 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 N2O 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 N2O emissions in BS treatments. Soil NO3− N and C/N were the most important soil properties affecting N2O 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 N2O 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.