Characteristics of annual nitrous and nitric oxide emissions from major cereal crops in the North China Plain under alternative fertilizer management

Although nitrogen fertilizer is crucially important for China's crop production, the overuses in the intensive cereal cropping systems of the North China Plain has caused extensive concern for its environmental consequences on nitrous oxide (N2O) and nitric oxide (NO) fluxes. To characterize the integration of environmental and agronomic aspects of fertilizer management, we conducted two annual winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation cycles under five fertilization treatments, including the farmers' conventional practice (CP) amended with synthetic nitrogen, three alternative managements of reduced nitrogen inputs with synthetic fertilizers alone (UA), synthetic fertilizers combined with poultry manure (UA + PM) or controlled-release urea combined with poultry manure (CU + PM), and the control without nitrogen fertilization (CK). The N2O and NO fluxes and direct emission factors varied seasonally and annually. These variations could be interpreted mechanically by a revised “hole-in-the-pipe” model and dual Michaelis-Menten and Arrhenius kinetics. The CK, CP, UA, UA + PM, and CU + PM treatments released N2O at 0.65, 4.64, 3.66, 2.88, and 2.40 kg N ha−1 yr−1, respectively, and NO at least 0.42, 2.35, 2.24, 1.30, and 1.18 kg N ha−1 yr−1, respectively. The annual direct emission factors of N2O and NO were 0.41-0.67% and 0.18-0.32%, respectively. The three alternative managements decreased both N2O and NO emissions, expressed either on an area basis or relative to grain yield, without sacrificing crop yields compared to CP. However, their mitigation effects on each gas emission were different. The UA treatment reduced only N2O emission, while UA + PM and CU + PM showed significant mitigation effects on both gases as compared to CP or UA. Overall, our results provide insight into environmental aspect of fertilizer management in major cereal crops and suggest that reducing nitrogen input coupled with organic manure incorporation could be beneficial for simultaneously mitigating nitrogen-containing trace gas fluxes and sustaining cereal grain yields.