| The dynamic change of NH4+, NO3- and TN, under the situation which urea was applied in the high fertility paddy-field in Yuhang of Hangzhou city with a lysimeter which was designed and made by ourselves, was studied and analyzed in order to find the rules of the change in the water-body of surface and the leakage rule of nitrogen, to reduce the effect of nitrogen loss on the water pollution. It has an important reality meaning to apply urea reasonable, to control nitrogen loss in the paddy-field and to protect water ecology and environment.The research results through the experiment on single-reason rice in 2002 indicated:1. After urea application, there are more NH4+ than NO3- in the water surface. This is not the same as the views of "the concentration of NO3- is more than that of NH4+'s". The variation of NH4+ and TN is that it attained the biggest values in the 1st day after urea application, then gradually decreased. However NO3- has the different change trends: in the 1st day after urea application, the difference of NO3- between N1~N4 and CK was not larger; in the 3rd day, the NO3- concentration of N1~N4 reached the biggest ones, then went down. This was the same as the change tendency of NH4+/TN> NO3-/TN and (MV+NO3-) /TN.2.Urea application can clearly increase the quality of NH4+ and TN. But the ability of which to increase the quality of NO3- was not so clearly. The biggest value of NO3- concentration only attended ISmg'L"1.while NH4+and TN reached 120 mg'L-1 and 210mg'L-1 , urea application can improve the ratio of NH4+ in the TN, decrease the ratio of NO3-. So NFLt+and TN were the mostly important nitrogen indexes to monitor the water pollution in the paddy-field, NO3- may be the assistant nitrogen index.3.In the 1st day after urea application, the amount ratio which came from the urea and N application to the water-body in the same time was basically between 16.99~44.21%. It increased with urea application amount increase. This indicated that urea application can increase the ratio that urea entered the water. But the concentration of NH4+ decreased to the very low level in 7-10 days after fertilizer was applied. Which showed that under inundation, with surface application andapplication-digging, the volatilization of NH3 was very strong in 7-10 days after fertilizer application,. It meant that with these two kinds of N application, there was a lot of fertilizer which entered the surface water. Obviously, these two kinds of N application can't attain the aim to make the best use of N application and to oring danger effect on water environment.4.The dynamic change of three kinds of nitrogen in the surface water-body indicated that the concentration of three kinds of nitrogen was higher in the first 9days after urea application, and the water layer was deeper. If the heavy rain took place, the ground flow easily produced and brought the Nitrogen away from the field. So these 9 days after N application was the critical time to prevent the nitrogen loss and the measures should be taken. N application only provided the likelihood of N loss, and heavy rain made the N loss come true.5.The dynamic change of the concentration of three kinds of nitrogen indicated that there was an positive relationship between the concentration of nitrogen in the surface water and N application amount. Therefore, it is useful to decrease nitrogen application amount or even with N application in split time so as to decrease the N loss and leaching in the paddy-field.6.To define and calculate Even Productivity of Nitrogen in the surface Water-body'of paddy field(EPNW), Marginal Productivity of Nitrogen in the surface Water(MPNW)and Elasticity Coefficient of Nitrogen in the surface Water(ECNW), indicated that EPNW and ECNW increased with N application amount increase, however MPNW has no the rule.7.The simulation models suited to express the dynamic change of the concentration of NH4+ and TN with time was non-linear model such as exponentiaK logarithmic logarithm and binomial. But NO3- had no appropria... |
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