| Ammonia volatilization and atmospheric wet deposition of nitrogen in field experiments were studied in rice-wheat rotation system at Changshu Agroecological Experimental station, CAS. Ammonia volatilization after urea application to fields was measured in chamber techniques. Factors that influence ammonia loss were studied also, such as climate condition, application techniques of nitrogen fertilizer, spraying surface films, nitrogen and phosphorus application rate, NH4+-N concentration of surface water in paddy soil. Atmospheric wet deposition of nitrogen was collected continuously at the station. Nitrogen deposition rates and its relation to nitrogen fertilizer application to fields were also investigated. The results obtained were summarized as follows:1. The peak of ammonia volatilization occurred within 1-3 days after urea application to paddy fields. Ammonia loss increased with nitrogen application rates, but the percentage of ammonia volatilization in fertilizers applied (the ratio of ammonia loss to N fertilizer applied) did not always increase. In terms of the whole periods of rice, ammonia loss rate varied from 16.66-75.21kg.hm-2, which amounts for 6.10%~20.65% of the total N applied. There was significant correlation between NHs loss and the NRt+-N concentration of surface water in paddy soil. The total ammonia loss and percentage in fertilizer applied in the three fertilization periods were different and this was caused by integrated effects of such factors as climate condition (ah" temperature, wind speed, sunshine, et al), the orders of rain and fertilization, nitrogen application rate and growth characteristic of rice. There was an evident annual difference of NHs loss in flooded rice caused by different climate conditions. Compared to normal fertilization way, spraying surface films reduced NHs loss by 4.12%-31.41%, while broadcasting of N fertilizer without stand water on the surface and then incorporation into soil could reduce NH3 loss by 38.86%-69.82%.2. The peak of ammonia volatilization occurred within 1-4 days after urea application in wheat fields, and the duration of NH3 loss was longer than in rice. Ammonia loss inwheat soils increased with nitrogen application rate but it was not true for the percentage of ammonia volatilization in N fertilizer applied. As far as the whole season of wheat was concerned, ammonia loss rate was 5.17~17.59kg. hm-2 , which amounts for 3.06-6.44%percentage of N fertilizer applied. The NHs loss and percentage in N fertilizer applied in wheat season were always lower than in rice season. Ammonia loss in wheat season occurred mainly in the period of basal dressing, but the different percentages in N fertilizer applied were found during the different fertilization periods. Compared to normal fertilization way, broadcasting of N fertilizer without stand water and then incorporation into soil could reduce NHs loss by 17.3%~35.7%. There was an evident annual difference of NHs loss in the two wheat seasons.3. Whether in paddy fields or in wheat fields, compared with the middle phosphorus application rate (90 kg P2O5.hm-2), both higher P application (180 kg P2O5. hm-2) and lower P application (30 kg P2O5.hm-2) increased the ammonia volatilization from urea, which were increased by 34.9%~37.1% and 28.3%~79.6% respectively in paddy fields, and 43.8%~53.8% and 5.4%~46.2% respectively in wheat fields.4. The rainfall occurred mainly from June to August in this area, which amounted for 41.8%~42.3% of the total rainfall within a year, and atmospheric wet deposition of N in this period amounted for 38.48%~50.38% of the total in the year. Wet deposition rate of N was positively correlated with rainfall, while the mean concentration of wet deposition of N was negatively correlated with rainfall. The dynamic changes of wet N deposition were mainly influenced by rainfall and fertilization. Nitrogen brought by wet deposition into soil or surface water in rice season varied from 6.89-17.50 kg. hm-2, of which NH4+-N amounted for 35.83%~65.93% with average means of 55.18 ?...
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