Organic fertilizers reduce N₂O and NH₃ emissions by regulation soil nitrogen pool and microbiome

Organic fertilizers are generally considered beneficial towards maintaining long term soil health, yet they could elevate N₂O and NH₃ emissions which raise concerns regarding air pollution and climate change. In this study, four types of organic fertilizers (raw sheep manure, RSM; composted sheep-manure organic fertilizer, OF; biochar-amended organic fertilizer, CharOF; sterilized OF, SOF) were applied onto three kinds of soils in microcosm cultivation to explore their effects on N₂O and NH₃ emissions and the underlining mechanisms. The results showed that traditional organic fertilizers (RSM and OF) significantly increased N₂O and NH₃ emissions from the soils, whereas CharOF reduced by as much as 23.0% in N₂O and 18.4% in NH₃ from that of RSM/OF peaks. Both OF and SOF significantly increased soil total nitrogen (TN) and organic nitrogen (Org-N), while CharOF significantly improved soil NO₃^--N, NH₄⁺-N and microbial biomass nitrogen (MBN). Metagenomic sequencing showed that RSM and OF significantly increased denitrification genes norB and narI, dissimilatory nitrate reduction genes nasA, napA and nirB, and mineralization gene ureC, while CharOF slightly suppressed denitrification genes nirS and narI, dissimilatory nitrate reduction genes nasA/B, napA, nirB and NR, and mineralization gene ureC. RDA analysis revealed that NO₃^--N, NH₄⁺-N, MBN and pH were the environmental factors affecting NC relevant genes and gas emissions. PLS-PM model revealed that soil nitrogen pool correlated stronger to the NH₃ and N₂O emissions than that of nitrogen cycle (NC) relevant genes. This study provides a theoretical foundation for the promotion of low-pollution fertilization practices in green agriculture, and contributes to the advancement of agricultural sustainability. Additionally, it offers fresh perspectives on organic fertilizer production and its role in enhancing socio-economic systems for public benefits.