Abstract: To explore N₂O and N₂ emissions from upland soils after nitrogen fertilizer application, a 60-day aerobic incubation experiment (25 ℃,80% water-filled pore space) using the ¹⁵N tracing method was conducted to quantify the N transformation, N₂O and N₂ emissions from maize soils from four sites (Harbin, Shenyang, Luancheng and Shouguang) and vegetable soils from two sites (Shen-yang and Shouguang), with urea being applied at 167 mg N·kg^-1 to simulate the field application rate of 200 kg N·hm^-2. The results showed that for the four sites with maize soils, the cumulative emission of N₂O was in the order of Shouguang (20 mg N·kg^-1) > Luancheng (14 mg N·kg^-1) > Shenyang (5 mg N·kg^-1) > Harbin (0.5 mg N·kg^-1) and the cumulative N₂ emission was in the order of Luancheng (176 mg N·kg^-1) > Shenyang (106 mg N·kg^-1) > Shouguang (75 mg N·kg^-1) > Harbin (12 mg N·kg^-1). For vegetable soils, the cumulative N₂O emission of Shouguang (21 mg N·kg^-1) was 10 times of that of Shenyang (2 mg N·kg^-1), but without differences in cumulative N₂ emissions (28 and 24 mg N·kg^-1, respectively). The N₂O/(N₂O+N₂) of the six soils ranged from 5% to 40%. The N₂O/(N₂O+N₂) of the two soils from Shouguang (30%-40%) was significantly higher than other four soils (1%-10%). Soil bulk N pool contributes to 56% of total N₂O emission and 61% of total N₂ emission, which was higher than the contribution of fertilizer. The cumulative N₂O emission was positively correlated with soil background pH, which indicated that soil background pH might be an important factor regulating N₂O and N₂ emission from upland soils. In the alkaline soil regions of North China Plain (such as Luancheng and Shouguang), mea-sures to reduce soil pH might have great impact on reducing N gaseous emission.

Key words: nitrous oxide, nitrogen, ¹⁵N tracing method, maize soil, vegetable soil