The Effects Of N Application Levels On N Use Efficiency In Rice Growth Stages And The Dynamic Variation Of N Leaching In Paddy Field

The effects of N application levels on N use efficiency in different rice growth stages and the dynamic variation of N leaching in paddy field is important to ensure sustainability of paddy soil fertility and to develop reasonable crop N nutrient management protocols.The changes of nitrogen content of rice organs and the dynamic characteristics of nitrogen(N)in surface water of paddy field under different N supply levels in Hangzhou,Zhejiang Province was studied from 2006 to 2007.The target of this research is to provide a better technical indexes to control N loss in the paddy field and to protect water ecology and environment.The research results through the experiment indicated:(1)The N contents of leaf,stem and root in different growth stages of rice had increased firstly and then declined,the maximum N content happened in pollen mother cell formation and meiosis stage.The content of panicle had gradually increased until mature stage.There was significant correlation between applied nitrogen levels with N content of various organs in rice.(2)The rice yield increased with N application amounts among proper range. Extra N application had no obviously effects on rice yield.The result in Hangzhou showed that yield reduced when N application amount exceeded 225 kg·hm^-2(N4)level between 2006 and 2007.(3)Nitrogen accumulation dynamic in soil showed that the long-term fertility of TN for rice crop growth could not be sustained whic was lower than 225 kg·hm^-2 (N4).The redundant N apply in soil may be the main reason leading to soil nitrogen accumulation and water pollution.(4)Considering the N use efficiency and rice yield and N leaching,It was suggested 225 kg·hm^-2(N4)level may be a better N application level in sandy loam soil.(5)During the growing periods of rice,N application within firstly 3 times greatly increased the concentration of ammonia nitrogen(NH₄⁺-N)and total nitrogen(TN)in surface water in paddy field,and then both declined subsequently as the time passed.After the nitrogen application,the concentrations of NH₄⁺-N and TN in the seventh day in 6 different treatments were separately below the 20%of the concentrations in the first day after N applied.So in terms of the environment consideration,the period within a week after the N fertilizer application was a critical time to control N runoff loss.(6)There was significant relativity between the concentration of nitrogen of surface water and N supply levels in paddy field.The correlations between N supply levels and the concentration of NH₄⁺-N,TN and NO₃^--N were very markedness(P＜0.01)in 2007,and the correlation in 2006 were also significant (P＜0.05).So the reasonable fertilization is very important to the control of pollution from paddy field.(7)The results indicated that the concentration of NH₄⁺-N was lower than that of NO₃^--N in the leakage water.During the whole growing period of rice,the concentration of NH₄⁺-N ranged from 0-8 mg·L^-1and concentrated in 0-1 mg·L^-1, while the concentration of NO₃^--N ranged from 0-25 mg·L^-1and concentrated in 1-10 mg·L^-1.The NO₃^--N dominated the main leaching form in the leakage water of paddy field(8)There was not significant correlation between the nitrogen content in leakage water and N supply levels(except elbow lysimeter in 2007).There was no clearly difference for the TN content in two years.The leaching amount of TN in the lysimeter in 2007 was 15-20 kg·hm^-2,which was higher than in 2006.