Mitigation of reactive nitrogen loss from arable soils through microbial inoculant application: A meta-analysis

Excessive N fertilizer application contributes to a surge in reactive N (Nr) emissions from agroecosystems, consequently threatening global ecosystems' quality and security. Adding functional microorganisms to agricultural soils, namely microbial inoculants (MI), is a promising method for ensuring sustainable agriculture, but general assessment of microorganism-driven N losses and mediating factors (such as climate conditions, soil properties, and field management practices) remains unclear. Therefore, a comprehensive meta-analysis on the effect of MI addition on NH3 volatilization, N2O emissions, and N leaching in soil-crop systems was conducted by integrating 50 published articles (188 paired observations). The MI application significantly reduced N2O emissions and NH3 volatilization by 29.8% and 24.9%, respectively. The boosted regression tree model showed that the soil organic carbon (SOC) and soil pH significantly affected the efficacy of MI application on both NH3 and N2O loss mitigation. The effects of MI application on N leaching were not clear due to limited data points. Additionally, MI addition significantly increased the abundance of denitrification functional genes (nirK, nirS, and nosZ). In conclusion, MI application presented a high potential to reduce Nr from croplands, future adoption of MI techniques should consider the effects of soil properties and field practices on its efficacy in order to achieving sustainable N management in crop production systems.