N2O and N2 emission characteristics from maize and greenhouse vegetable soils in Northern China

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.