Assessment of the crucial factors influencing the responses of ammonia and nitrous oxide emissions to controlled release nitrogen fertilizer: A meta-analysis

Reducing ammonia (NH3) and nitrous oxide (N2O) emissions have great effects on mitigating nitrogen (N) nutrient loss and greenhouse gas emissions. Controlled release urea (CRU) can control the N release rate, which reduces reactive N loss and increases nitrogen use efficiency relative to conventional urea (CU). However, the crucial factors influencing the responses of NH3 and N2O emissions to CRU relative to CU are still unclear. In this study, we evaluated the responses of NH3 and N2O emissions to CRU based on collected field data with a meta-analysis. CRU reduced the NH3 and N2O emissions by 32.7 and 25.0% compared with CU, respectively. According to subgroup analysis, CRU presented better mitigation of NH3 and N2O emissions in soils with pH 6.5-7.5 (-47.9 and -23.7%) relative to either pH<6.5 (-28.5 and -21.4%) or pH>7.5 (-29.3 and -17.3%), and in the rice season (-34.8 and -29.1%) relative to the wheat season (-19.8 and -22.8%). The responses of NH3 and N2O emissions to CRU increased from rainfed (-30.5 and -17.0%) to irrigated (-32.5 and -22.9%), and then to paddy (-34.8 and -29.1%) systems. In addition, the response of N2O emission mitigation increased with increases in soil total nitrogen (TN); however, soil TN did not significantly affect the response of NH3 volatilization. The reduction in NH3 emission was greater in sandy-textured soil (-57.7%) relative to loam-textured (-32.9%) and clay-textured (-32.3%) soils, whereas soil texture did not affect N2O emission. Overall, CRU was a good option for reducing the NH3 and N2O emissions relative to CU in agricultural production. This analysis improves our understanding of the crucial environmental and management factors influencing the mitigation of NH3 and N2O emissions under CRU application, and these site-specific factors should be considered when applying CRU to reduce reactive N loss and increase NUE.