The Effect Of Different Nitrogen Application Rate On Paddy Ammonia Volatilization And Ecological Threshold Of Nitrogen Input

In this paper,a kind of rice,which was named as Mingzhu 2 and planted in Jiaxing Zhejiang province,was chosen as the research object.Through the simulation of leakage with undisturbed paddy soil columns,the relationship among the amount of nitrogen application,rice production and ammonia volatilization was studied,helping confirming the safe threshold level of nitrogen input to maintain environment and food security,which is important to stable food security and reduce agricultural nonpoint source pollution.The main results are as follows:(1)Rice yield was significantly influenced by N application,the increase of N fertilizer can promote the yield of rice when N application rate was less than 258.6 kg/hm2,the N application rate was 258.6 kg/hm2,which had the biggest rice yield in the experiment but rice yield would decrease if continued to increase the amount of N fertilizer.With the amount of nitrogen increasing,the rice nitrogen utilization showed downward trend,the nitrogen utilization rate of highest yield was only about 37%.With the increasing of nitrogen amount,nitrogen apparent loss increased,the maximum nitrogen losses was as high as 60%.(2)Ammonia volatilization is one of the main approach of paddy nitrogen loss,the ammonia volatilization of test paddy was very strong after fertilization,the whole process of ammonia volatilization was a short duration,probably within a week after fertilization,and the intensity of ammonia volatilization after base fertilizer was much higher than the top dressing.After fertilization,ammonia volatilization rate increased first and then decreased,the peak usually occured in the first day to the third day after fertilization,the peak of base fertilizer in 2013 occurred in the first day,the peak was 83.74 kgN/(hm2·d),and the top dressing appeared two small peaks,respectively in the second day and the seventh day,the peak was 14.95 kgN/(hm2·d)and 8.08 kgN/(hm2·d);in 2014,the peak of base fertilizer turned up in the third day,the peak was 35.96 kgN/(hm2·d),and the top dressing occurred in the second day,the peak was 12.62 kgN/(gm2·d).Paddy ammonia volatilization was notable different under varying nitrogen,especially under the conditions of high nitrogen fertilizer,through the data fitting,ammonia volatilization increased exponentially with the amount of nitrogen,the N application rate was 213.6 kg/hm2,which was the inflection point of ammonia volatilization.(3)Ammonia volatilization rate was affected by many factors,including the amount of nitrogen,the period of fertilization,the concentrations of NH4+-N in surface water,the pH in surface water,temperature,rainfall and so on.(4)Considering food security,economic and environmental safety based on ammonia volatilization,the recommended threshold level of nitrogen input in Jiaxing area ranged from 220.99?255.45 kg/hm2.