Global evaluation of inhibitor impacts on ammonia and nitrous oxide emissions from agricultural soils: A meta-analysis

Inhibitors are widely considered an efficient tool for reducing nitrogen (N) loss and improving N use efficiency, but their effectiveness is highly variable across agroecosystems. In this study, we synthesized 182 studies (222 sites) worldwide to evaluate the impacts of inhibitors (urease inhibitors [UI], nitrification inhibitors [NI] and combined inhibitors) on crop yields and gaseous N loss (ammonia [NH3] and nitrous oxide [N2O] emissions) and explored their responses to different management and environmental factors including inhibitor application timing, fertilization regime, cropping system, water management, soil properties and climatic conditions using subgroup meta-analysis, meta-regression and multivariate analyses. The UI were most effective in enhancing crop yields (by 5%) and reducing NH3 volatilization (by 51%), whereas NI were most effective at reducing N2O emissions (by 49%). The application of UI mitigates NH3 loss and increases crop yields especially in high NH3-N loss scenarios, whereas NI application would minimize the net N2O emissions and the resultant environmental impacts especially in low NH3-N loss scenarios. Alternatively, the combined application of UI and NI enables producers to balance crop production and environmental conservation goals without pollution tradeoffs. The inhibitor efficacy for decreasing gaseous N loss was dependent upon soil and climatic conditions and management practices. Notably, both meta-regression and multivariate analyses suggest that inhibitors provide a greater opportunity for reducing fertilizer N inputs in high-N-surplus systems and presumably favor crop yield enhancement under soil N deficiency situations. The pursuit of an improved understanding of the interactions between plant-soil-climate-management systems and different types of inhibitors should continue to optimize the effectiveness of inhibitors for reducing environmental losses while increasing productivity.

Automated summary

Inhibitors are considered efficient in reducing nitrogen loss and improving nitrogen use efficiency, but their effectiveness varies across different agroecosystems. Urease inhibitors enhance crop yields and reduce ammonia emissions, while nitrification inhibitors are effective at reducing nitrous oxide emissions. The application of inhibitors is dependent on factors such as soil properties, climatic conditions, and management practices. Understanding the interactions between plant-soil-climate-management systems and different types of inhibitors is crucial for optimizing their effectiveness in reducing environmental losses and increasing productivity.