Input of nitrogen (N) is essential for high crop yields, but excessive application of N fertilizer increased the loss of gaseous nitrogen. Gaseous loss of N is a main way of nitrogen loss in the paddy fields of the irrigation area. The static chamber-gas chromatograph method was used to measure the N₂O emission from the paddy field. The five N treatments of field experiment were conducted, including two treatments of the conventional N application rate (300 kg/hm²), i.e the application of only urea (N300) and the application of the organic fertilizer (manure) with the urea nitrogen (N300-OM); two treatments of the optimized N application rate (240 kg/hm²), i.e, the application of only urea (N240) and the application of the organic fertilizer (manure) with the urea nitrogen (N240-OM), and no N fertilizer application plot (CK).
The results showed that N₂O emissions mainly occurred before the tiller stage or at the pre- and late- rice growth stages, and more N₂O emissions were measured after rice planting and irrigation. At different nitrogen levels, the total amount of N₂O emissions during the whole rice growing season varied among 2.69-3.87kg/hm², and the loss of fertilizer N due to N₂O emissions was only 0.43%-0.64%. N₂O emissions from the paddy field is not an important way of nitrogen loss at the Yellow River irrigation area, but the warming potential through N₂O emissions in the irrigation area is not neglectable. Excessive application of nitrogen fertilizer in the paddy field significantly increased N₂O emissions, and at the same level of nitrogen application, organic fertilizer amendment increased N₂O emissions from the paddy soil (P<0.01). Optimization of nitrogen application in the irrigated paddy field during the rice growing season reduced N₂O emissions. With the conventional irrigation practice, N₂O emissions from paddy fields in N300-OM treatment reached 3.87kg/hm². In the scales of 100a, the global warming potentials (GWPs) were 20.76×10⁷ kg CO₂/hm². Optimization of N application in the irrigated paddy field during the rice growing season reduced N₂O emissions. Compared with N300-OM treatment, cumulative N₂O emissions in N240 and N240-OM treatments decreased by 1.18 kg/hm² and 0.57 kg/hm², respectively. In the scales of 100a, GWPs caused by N₂O emissions in the paddy field decreased 6.33×10⁷ kg CO₂/hm² and 3.06×10⁷ kg CO₂/hm², respectively.