| The amount of nitrogen losses is great with various losing ways because of the excessive fertilization in vegetable crop-soil system.Except being absorbed by crop, nitrogen is easily losed form NH3 volatilization, nitrification-denitrification, runoff and leaching, and then form air pollution and ground and surface water contamination, furthermore it brought the enormous pressure to the environment. In the same time,vegetables nitrate pollution is occurred frequently because of absorbing excessive nitrate, which is closely related to human’s health. Currently, the fate of nitrogen and the pathways of nitrogen loss still lacked the systematic quantitative field research in situ examination on vegetable crop-soil system. In this research, nitrogen use efficiency, soil residue and the various losing ways of nitrogen including NH3 volatilization, nitrification-denitrification loss,runoff and leaching were monitored by using field plot and microplot 15N tracer experiments, and the nitrogen loss was evaluated so as to provide some important information for establishing optimized nitrogen management, diminishing nitrogen losses and increasing nitrogen use efficiency.The results indicated that the fate of nitrogen in eggplant field displayed by difference methods fertilizer loss>soil residue>crops uptake under the 225 kg·hm-2 nitrogen application rate, the content of them were 86.4,62.6 and 61.7 kg·hm-2, according for 38.4%,27.9% and 27.5% of the applied nitrogen fertilizer, respectively. Under the 450 kg·hm-2 nitrogen application rate, soil residue>fertilizer loss >crops uptake, the corresponding date were 196.2,195.9 and 42.7 kg-hm"2, and according for 43.6%,43.5% and 9.5% of the applied nitrogen fertilizer, respectively. Namely along with the nitrogen application rate increased, the nitrogen use efficiency remarkablely decreased (P<0.01), the residual fertilizer nitrogen remarkablely increased, the loss of fertilizer nitrogen remarkablely increased.The fate of nitrogen in eggplant field displayed by 15N-tracer method fertilizer loss >crops uptake>soil residue under the 225 kg·hm-2 15N application rate, according for 39.8%,34.4% and 25.8% of the applied nitrogen fertilizer, respectively. Under the 450 kg·hm-2 15N application rate, fertilizer loss >crops uptake>soil residue, and according for 49.9%,27.7% and 22.4% of the applied nitrogen fertilizer, respectively. Namely along with the nitrogen application rate increased, the nitrogen use efficiency remarkablely decreased (P<0.05), the residual fertilizer nitrogen remarkablely increased, the loss of fertilizer nitrogen remarkablely increased.The nitrogen use efficiency calculated by 15N-tracer method was higher than by difference methods. And the crops uptake from nitrogen fertilizer increased significantly (P<0.05), the uptake form soil reduced significantly.The nitrogen loss by different ways was leaching> NH3 volatilization> nitrification-denitrification> runoff. Nitrogen leaching loss was 43.2 and 91.5 kgN·hm-2, NH3 volatilization was 22.5 and 49.7kgN·hm-2, denitrification loss was 6.2 and 22.3kgN·hm-2 and runoff loss was 7.6 and 21.0kgN·hm-2, according for 19.2% and 20.3%,10.0%and 11.0%,2.8% and 5.0% and 3.4% and 4.7% of the applied nitrogen fertilizer, respectively.The N2O emission quantity of nitrification-denitrification was 13.1 and 33.7 kgN·hm-2, according for 5.8% and 7.5% of the applied nitrogen fertilizer.The nitrogen loss by 15N-tracer method was NH3 volatilization> nitrification-denitrification> runoff> leaching under the 225 kg·hm-2 15N application rate, which according for 10.0%,5.8%,3.4and 1.4% of the applied nitrogen fertilizer, respectively. Under the 450 kg·hm-2 15N application rate, NH3 volatilization> nitrification-denitrification> leaching> runoff, the corresponding dates were 11.0%, 7.5%,4.8% and 4.7% respectively.The temperature and the ammonia partial pressures on the surface soil were the important factors with the ammonia volatilization.The soil water content was the important limited factor for denitrification and N2O emission occurring in the soil, and the NH4+-N and NO3--N concentration of soil was closely related with denitrification and N2O emission. The loss of runoff was remarkablely increased by by rainfall. At the same time, rainfall also increased the risk of nitrogen leaching loss. |
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