Global impact of enhanced-efficiency fertilizers on vegetable productivity and reactive nitrogen losses

Vegetables are the most consumed non-staple food globally, and their production is crucial for dietary diversity and public health. Use of enhanced-efficiency fertilizers (EEFs) in vegetable production could improve vegetable yield and quality while reducing reactive nitrogen (Nr) losses. However, different management and environmental factors has significantly distinctive impacts on the effectiveness of EEFs. In this study, a worldwide meta-analysis based on the data collected from 144 studies was performed to assess the impacts of EEF (nitrification inhibitor [NI] and polymer-coated urea [PCU]) application on vegetable yield, nitrogen (N) uptake, nitrogen use efficiency (NUE), vegetable quality and Nr losses (nitrous oxide [N₂O] emissions, ammonia [NH₃] volatilization, and nitrate [NO₃^-] leaching). The effects of the applied EEFs on vegetable yields and N₂O emissions were assessed with different management practices (cultivation system, vegetable type and N application rate) and environmental conditions (climatic conditions and soil properties). Compared to conventional fertilizers, EEFs significantly improved vegetable yield (7.5-8.1 %) and quality (vitamin C increased by 10.7-13.6 %, soluble sugar increased by 9.3-10.9 %, and nitrate content reduced by 17.2-25.1 %). Meanwhile, the application of EEFs demonstrated a great potential for Nr loss reduction (N₂O emissions reduced by 40.5 %, NO₃^- leaching reduced by 45.8 %) without compromising vegetable yield. The NI was most effective in reducing N₂O emissions (40.5 %), but it significantly increased NH₃ volatilization (32.4 %). While PCU not only significantly reduced N₂O emissions (24.4 %) and NO₃^- leaching (28.7 %), but also significantly reduced NH₃ volatilization (74.5 %). And N application rate, soil pH, and soil organic carbon (SOC) were the main factors affecting the yield and environmental effects of EEFs. Moreover, the yield-enhancing effect of NI and PCU were better at low soil N availability and SOC, respectively. Thus, it is important to adopt the appropriate EEF application strategy targeting specific environmental conditions and implement it at the optimal N application rate.