Effects Of Nitrogen Application On N₂O Emission From Vegetable Soil

As one of the most important greenhouse gases, nitrogen dioxide (N₂O) has drawn worldwide attention due to its substantial contribution to global warming and ozone depletion. Agricultural soil is a major source of anthropogenic N₂O emission. With the adjustment of planting stucture, the area of vegetable land has been increasing in China. Therefore, understanding N₂O emission flux and patterns in vegetable land, and factors influencing the emission is of great importance to assess agricultural N₂O emission at both regional and national scales. Furthermore, it also plays an important role in modeling N₂O production. In this study laboratory incubations and outdoor lysimeter and field experiments were conducted to study effects of different nitrogen fertilizers on N₂O emission from yellow brown soil; denitrification loss and N₂O emission in yellow brown soil and fluvo-aquic soil; effects of N application rates on N₂O emission from vegetable field. The main results were as follows:1. The inorganic nitrogen fertilizers applied in fields were an important source of atmospheric N₂O. The application of nitrogen fertilizers significantly enhanced N₂O emission (P＜0.05) and the effects varied with fertilizers. At all levels of soil moisture contents, N₂O emissions in Urea treatment were significantly greater than those in treatments of NH₄HCO₃ (A. B) and (NH₄)₂SO₄ (A. S), and accounted for 0.40 %-6.46 % of total N input. At moisture content of 35%, N₂O emissions in A. S treatment were significantly greater than that in A. B treatment, and accounted for 2.95 % of total N input.2. There was a significant correlation between soil moisture levels and N₂O emissions with or without fertilization (F=1913.48, P＜0.05). N₂O emissions increased significantly (P＜0.05) with soil moisture contents increasing, and also the N₂O-N losses of nitrogen fertilizers and emission factors were enhanced significantly. This could be concluded that soil moisture content is the most important factor controlling N₂O emission when other conditions were the same.3. The application of N fertilizers significantly enhanced N₂O emissions and denitrification losses in yellow brown soil, (P＜0.05), but had not resulted in significant changes of N₂O emissions and denitrification losses in fluvo-aquic soil.4. With or without N fertilization, the changes of N₂O emission or deritrification losses with incubation time could be well predicted by a modified Elovich equation: y=bln(t)+a。5. The N₂O emission flux reached the peak at 9 am or 1 pm and the lowest point at 4 pm. The N₂O emission flux also showed a seasonal changing pattern that it was highest in Spring (Apr. -Jun), and lowest in Summer (Jul. -Aug); the emission flux was moderate in Autumn and Winter.6. N₂O emission in both lysimeter study and field experiment were greatly enhanced by the application of N fertilizer. There was a significant correlation between N₂O emissions and the application rate of N fertilizer (r²=0.800, P＜0.01, n=36 lysimete; r²=0.757, P＜0.01, n=15 field). The N₂O emission amounts were increase significantly (P＜0.05) when N was over- applied. The highest amount of N₂O emissions was 4.98 kg/ha (Field). The N₂O-N losses of N fertilizer were also greatly enhanced by application of N fertilizer, and they ranged fom 0.260-2.093 kg N/ha. N₂O emission factor, ranging from 0.13 %-2.04 %, had no significant relationship with N application rates.7. The yield of vegetables increased with N application rates increasing up to a moderate level (N-3 of lysimete and N-3 of field). At the same time N₂O emission remained at a low level. There was a significantly correlation between the N₂O emissions and yield of vegetable (r²=0.583, P＜0.01, n=36 lysimete; r²=0.540, P＜0.05, n=15 field).There was a significant correlation between the application rate of nitrogen fertilizer and N₂O emission, so it should be considered when mitigation options for reducing application rate of nitrogen fertilizer are proposed.