Global Meta-Analysis of Individual and Combined Nitrogen Inhibitors: Enhancing Plant Productivity and Reducing Environmental Losses

Abstract

Nitrogen (N) transformation inhibitors have been widely recognized as a promising strategy to enhance crop productivity and mitigate N losses. However, the effectiveness of individual or combined inhibitors can vary significantly across different agroecosystems. Using meta-analysis and cost–benefit analysis (CBA), we synthesized findings from 41 peer-reviewed studies (285 observations) globally to evaluate the efficacy of urease inhibitors (UIs), nitrification inhibitors (NIs), and combined inhibitors (UINIs). We assessed their influence on soil inorganic N transformations, greenhouse gas emissions, and crop productivity across diverse climates, soil types, cropping systems, and fertilization practices. Our results indicated that combined UINIs were the most efficient, increasing crop yields by 5% and mitigating gaseous emissions by 51% compared to UIs or NIs alone. UINIs achieved these benefits by enhancing crop ammonium (NH₄⁺) availability through regulating urea hydrolysis and prolonging NH₄⁺ retention by suppressing nitrification in the soil. The CBA revealed that the overall economic benefits of UINIs application outweighed the costs, resulting in a net monetary benefit of $23.36 ha⁻¹, equivalent to a 6.4% increase in revenue. Both meta-regression and random forest analyses suggested that UINIs performance was strongly influenced by factors such as N application rate, organic matter content, and soil pH. Notably, more substantial responses were observed in fine-textured soils and/or crops exposed to high N fertilization rates. Acidic soils (pH < 6.5) exhibited the largest effect sizes, with increased crop productivity and reduced NH₃ volatilization due to specific inhibitory interactions. In conclusion, these findings highlight UINIs beneficial impacts on crop productivity and environmental conservation, achieving a “win-win” scenario by addressing various N-loss challenges while enhancing economic outcomes. Further exploration and optimization of the interaction between climate, soil, plant, and management systems and the use of appropriate inhibitors are crucial for maximizing their positive impact on global climate and reaping corresponding economic benefits.