Study On The Effect Of Nitrogen Fertilizer With Split Application On Variation Of Nitrogen In The Surface And Leakage Water Of The Paddy Field

Nitrogen is a major factor for maintaining crop yield, getting better economic return. It also produces some severe environmental pollution problem when it was over and unreasonable used. The paper studies the dynamic characteristics of nitrogen (N) and phosphorus (P) in surface water of paddy field under different N supply levels in 2003. The dynamic variation of N leaching and its amount loss in paddy field under 5 different N treatments in 2003 and the simulation experiment in the pots in 2004 using a self-designed lysimeter with independent irrigation system were arranged in the paddy field located in Yuhang and Hangzhou. It was studied and analyzed in order to find the rules of the N loss in the water-body. A reference for Appling urea reasonable, controlling N loss in the paddy field and protecting water ecology and environment is provided. The research results through the experiment indicated:( 1 ) Split N fertilizer application with 4 times greatly increased the concentration of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN) in surface water in the field initially, then both declined subsequently as the time passed. After the first N application, The ninth day's concentrations of NH₄⁺-N and TN in 6 different treatments was separately 1.19%².70% and 6.03%¹8.74% (except CK) separately as comparing the first day's one. The rate of NH₄⁺-N/TN had the similar trend as TN, NH₄⁺-N.(2) The concentration of nitrate nitrogen (NO₃^--N) was lower than the one of NH₄⁺-N and the maximum concentration was 2.07 mg/L in the surface water. It also showed different trends from TN and NH₄⁺-N and the peak concentration value appeared after urea employed 3 days later each time. The same amount of P application in different N fertilizer application treatments showed different results that P concentration varied in the surface water. The P concentration in surface water of paddy had some relationships to N fertilizer application amounts. More N fertilizer application amount produced more P content in surface water of paddy field. In terms of the environment consideration, the period within 9 days after the fertilizer application was a critical time to control N, P loss and leaching from flooded paddyfield.(3) NH/-N and NCV-N concentration of the leakage water remained at a very low level during the whole growing period of rice, which were lower than lmg/L. The main leaching form in the leakage water was dominated by NCV-N. N loss from leaching in this experiment increased gradually with fertilizer applications increase. After the application of fertilizer for each time, the concentration of NCV-N in different treatments increased rapidly during a short period and then decreased gradually. The concentration dynamic patterns of NH4+-N had the similar trends and regularity as NCV-N, but it showed the peak concentration value of NH4+-N exceeded that of NO3'-N.(4) There were significant correlation between N fertilizer applied and the accumulative amount of NH4+-N, NCV-N and TN of the leakage water in the lysimeter of different treatments in the field and the coefficient is 0.933*,0.984**,0.982** respectively. Based on the point of economy and environment consideration, it is suggested that 75-150 kg/hm2 in Paddy field with sticky soil texture and higher fertility could be reasonable for better yield and reduce the N leaching. The period within a week after the N fertilizer application was critical time to control N leaching from paddy field, especially for the first N fertilizer application in paddy field.(5) The concentration of the leakage water in different treatments of the pots in the net room increased gradually with fertilizer applications increase. The differences of N concentration between treatment N-I (no N fertilizer application treatment) and treatment N-III (N fertilizer application 300kg/hm2) were significant .The NH4+-N concentration of the pots in the net room was lower than that in the paddy field for the same proportion N fertilizer application. The NO3'-N concentration was quite the contrary. Quantitative models with best coefficient for TN and NCV-N concentrations in the leaching water of the pots after N fertilizer application were cubic and quadratic.(6) The leakage amount of N was increased with fertilizer applications increase, but there is no significant difference among the treatments of the pots. The leakageamount of NCV-N and NH/-N are about 35% and 10% of that of total nitrogen amount, respectively. Paddy yields based on leaching cost of showed the pollution cost increased with the amount of N fertilizer application increase with producing lton paddy yield.(7) On the basis of the net room leakage amount of N, the relation between the leakage amount and the N fertilizer application was showed by the math expression. NH/-N: y=-7X10"V+0.0008x+0.0547 (R2=0.948**) NO3"-N:: y=3.4X10V+0.0003x+0.388 (R2=0.988**) TN: y=1.7X10-5x2-0.0014x+1.095 (R2=0.985**)(y express "leakage amount", x press "nitrogen application", unit "kg/hm2" )...