Using Vensim To Simulate The Dynamic Course Of Nitrogen In Paddy Field

The application of chemical nitrogen fertilizer dosage in China is the most in the world, and there exists superfluous nitrogen fertilizer application in various farm crops production. Quantification of nitrate losses is important for devising measures to ensure sustainability of soil fertility and groundwater resources and for the development of crop nutrient management protocols. The paper studies the dynamic characteristics of nitrogen (N) in surface water of paddy field under N supply levels in 2006. The dynamic variation of N leaching and its amount loss in paddy field under 5 different N treatments in 2006, using a self-designed lysimeter with independent irrigation system were arranged in the paddy field located in Fuyang and Hangzhou. Then the dynamic model was built to simulate the conversion process of nitrogen in paddy field using Vensim. The model was calibrated by the data observed in Yuhang, and validated by the data observed in this time. A reference for applying 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 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. So in terms of the environment consideration, the period within a week after the fertilizer application was a critical time to control N loss.(2) There was significant relativity between the concentration of nitrogen and N supply levels. The correlations between N supply levels and the concentration of NH₄⁺-N, TN and NO₃^--N were very high (P<0.01) in Fuyang and the correlation of them in Hangzhou were also significant (P<0.05) . So the reasonable fertilization is very important to the control of pollution from paddy field.(3) It was the trend that the concentration of NH₄⁺-N is lower than that of NO₃^--N in the leakage water. During the whole growing period of rice, the concentration of NH₄⁺-N was in the range of 0-15 mg/L and concentrated in 0-1mg/L, while the concentration of NO3-N ranged of 0-10 mg/L and concentrated in 1-4 mg/L. The main leaching form in the leakage water was dominated by NO₃^--N.(4) The correlation between the content of nitrogen in leakage water and N supply levels was not significant and this was different from the case of concentration of nitrogen in surface water. There was big different of the content of TN in two locations. The content of TN in the lysimeter in Hangzhou was 50-100mg/L while it was 100-200 mg/L in Fuyang. The reason of this condition is possible the field management of Fuyang was worse than that of Hangzhou.(5) It could be learnt from the result of the simulation of the model that the simulated data was perfect fit with the observed data in Hangzhou and FuYang. The result of Independent T Test between the observed data in Hangzhou and the simulated data was P>0.05=0. 516, and it was P>0.05=0. 610 in Fuyang. It indicated that there was correlation of the application of the model and the calibration data and localization in the application of the model.