Nitrogen Application Effect on Maize Yield, NH3, and N2O Emissions in Northeast China by Meta-Analysis

Abstract

Ammonia volatilization (NH3) and nitrous oxide (N2O) emission are the main underliers of nitrogen loss in farmlands, which can decrease nitrogen use efficiency and trigger environmental problems regarding greenhouse effects. Previous studies have regional limitations and lack universal guiding significance, as they are primarily based on individual experiments related to the effects of applying nitrogen fertilizer on maize. In this study, we performed a meta-analysis on a regional scale to investigate the overall impact of nitrogen fertilizer application on maize yield, N2O, and NH3 in Northeast China. The database included 85 studies and 1147 pairs of experimental data that were analyzed. The results showed that applying nitrogen fertilizer significantly increased maize yield, N2O emissions, and NH3 volatilization effects, and the growth rates (E) were 50.64%, 64.39%, and 69.25%, respectively. In Northeast China, the average emission factors of N2O and NH3 were 0.72% and 8.21%, respectively. The optimum nitrogen application rate for maize in Northeast China was 205 kg ha−1, resulting in 8.37% nitrogen loss (through N2O and NH3). Soil texture, alkaline nitrogen (AN) content in the soil, mean annual precipitation (MAP), nitrogen application rate, and fertilizer type were the key influential factors affecting changes in maize yield and N loss (N2O and NH3). Yield-scaled N2O and NH3 were found to be the significant emission reduction parameters that ensured maize yield. However, there was a remarkable ‘seesaw effect’ between yield-scaled N2O and NH3 under the same natural conditions (MAP and soil texture). Therefore, human activities such as reducing N surplus in soil, and N fertilizer application rate, along with selecting suitable fertilizer types should be given more attention to reduce yield-scaled N2O and NH3. Moreover, minimizing NH3 and N2O dual emission should be the main objective for green agriculture in Northeast China, rather than over-emphasizing on single emission reduction.