Enhanced-efficiency nitrogen fertilizer (EENF), developed to improve synchronization between crop nitrogen demand and nitrogen supply, can guarantee global food security and mitigate nitrogen fertilizer-induced environmental consequences. However, comprehensive assessments of how EENF affects CH4 and CO2 emissions from paddies and drylands and the associated benefits are lacking. Here, we present the results of a global meta-analysis conducted to assess the above issues. Our results showed that, on average, applying nitrification inhibitors and coated controlled-release urea to paddy fields significantly decreased CH4 emissions by 24.0 % and 25.3 %, respectively, likely due to the weakened inhibition of NH4+ on CH4 oxidation. A similar effect on CO2 emission was observed when farmers used nitrification inhibitors and coated controlled-release urea in the drylands. The meta-analysis results revealed that all EENF products could help mitigate the global warming potential of paddies and drylands. After incorporating the benefit of global warming potential mitigation into the cost-benefit analysis, coated controlled-release urea application in paddies and drylands produced the largest environmental gains of $ 76.34 ha-1 and $ 79.35 ha-1, respectively. However, the relatively lower purchasing cost and larger yield increase of urease inhibitors resulted in the largest net profits for farmers. Moreover, a greater economic return was generally achieved by applying EENF to paddy fields than by applying EENF to drylands. These findings highlight the role of EENF in mitigating the global warming potential of global paddy and dryland fields, which has facilitated the comprehensive recognition of EENF-induced impacts.

Application of coated controlled-release urea (CRU) has been widely recognized as an effective measure to improve crop yield while alleviating N fertilizer-induced environmental consequences. However, the overall effect of CRU on crop yield across field sites remains uncertain, especially for CRU applied at a reduced rate and frequency or blended with urea. Here, we applied a meta-analysis approach to address these issues. Our results indicated that applying CRU at an equal N rate significantly increased crop yield by 9.2% compared with conventional urea. The increase in crop yield was positively correlated with soil organic matter content and with the N release period of CRU but negatively correlated with mean annual temperature. However, reducing CRU application times brought a smaller yield increase (7.0%), although it could save labor and mechanical cost. Moreover, lowering CRU-N application rate had no significant effect on crop yield, mainly due to the reduced application frequency. This effect can be further weakened with the decreasing CRU-N application rate. In contrast, one-time application of a CRU-urea blend still exhibited superior efficiency, with a 9.8% increase in crop yield. Our findings showed that there existed a trade-off between the saving of CRU input cost and crop yield gain. However, a win-win scenario that attains more yield increase while saving input cost can be achieved through one-time application of a CRU-urea blend.

It is widely recommended that enhanced efficiency nitrogen fertilizers (EENFs; urease inhibitors, nitrification inhibitors, urease and nitrification inhibitors combined, coated controlled-release urea) be applied to croplands to improve N use efficiency and crop yield via regulating N transformations. However, EENFs may inevitably affect soil C dynamics for the coupled relationship between soil carbon (C) and N biogeochemical cycles. Yet, a comprehensive assessment of the effects of EENFs on soil C dynamics is lacking. Here, we conducted a global meta-analysis using 67 publications to assess the overall effects of EENFs on soil CH4 production, CO2 emission, organic C (SOC) content, dissolved organic C (DOC) content, microbial biomass C (MBC) content under different environmental and management conditions (climate conditions, soil properties and fertilizer management practices). Our results showed that on average, compared to conventional N fertilizer, EENFs with the same amount of N fertilizer have a non-significant impact on CH4 emission, which further depended on environmental and management conditions. Best scenarios for CH4 reduction included: paddy field (25.8%), urease inhibitor (26.9%) and medium N application rate (150-300 kgN ha-1; 23.6%), mainly due to the decreased stimulation of NH4+ on CH4 production; acid soil (33.7%), which was attributed to the enhanced methanotrophic communities' activities. The positive effect was also amplified by the increased mean annual precipitation and soil clay content that facilitated CH4 production. Contrarily, EENFs significantly reduced CO2 emission by 9.3%. The greater reduction was observed for the conditions producing more CO2 after fertilization, i.e. field experiment, alkaline soils, low soil inorganic N content and high N application rate (>= 300 kgN ha-1). Nitrification inhibitors and coated N fertilizer were the best available options as they can reduce inorganic C dissolution in calcareous soil and SOC mineralization, respectively. Besides, EENFs application did not significantly alter SOC, DOC and MBC contents. Our findings highlighted the role of EENFs played in decreasing soil C emission in agroecosystems.