| With the extensive use of chemical fertilizers, the problems of soil nitrate nitrogen accumulation, soil acidification and soil secondary salinization are increased, the agricultural sustainable development of our country has been seriously affected. To meet these problems, this paper made the fertilizer and soil temperature as factors under the indoor constant temperature culture condition, to study soil nitrate nitrogen transformation rule and the dynamic change process of physicochemical properties under the different fertilizer and temperature coupling condition, with a view to provide theoretical support for the efficient use of nitrogen fertilizer.The specific results are as follows:1.Research of soil nitrate nitrogen transformation and its dynamic characteristics under the coupling condition of fertilizer and temperature.(1) By studying the change rules of soil nitrate nitrogen content under the different temperature conditions, we can found the change trend of soil nitrate nitrogen content under each temperature treatment conditions are divided into three stages: slow stage, the maximum rate stage and lag phase. When the nitrogen application unchanged, with the temperature rises, the nitrate nitrogen content of each treatment required less time to reach equilibrium and the maximum cumulative amount is increasing.(2) The trend of soil nitrate nitrogen content under different fertilizer conditions is also consistent, it divided into slow, the maximum rate and lag phase three stages. When the temperature unchanged, the 244mg/kg nitrogen application level required the least time to reach equilibrium of each treatment, the 427mg/kg nitrogen application level required the maximum time to reach equilibrium. When the same reaction time, the nitrate nitrogen content of 244mg/kg treatment is minimum and the 427mg/kg treatment is maximum.(3)It showed that the maximum cumulative amount of high temperature and high nitrogen application treatment is 1.5 times than the low temperature and low nitrogen application treatment. The earliest to reach equilibrium is the treatment of 35℃ and 244mg/kg, it is13 d, the latest to reach equilibrium is the treatment of 15℃ and 427mg/kg, it is up to 51 d, the treatment of high temperature and low nitrogen required time to reach equilibrium is significantly less than the treatment of low temperature and high nitrogen.(4) Soil nitrate nitrogen accumulation can be quantitative described by the Logistic growth curve N a(1 cebt)?? ?.The fitting parameters of maximum nitrification rate and period of delay obtained from the model can be used to reflect the speed of soil nitrate nitrogen transformation process under the fertilizer and temperature coupling conditions. Factors of affecting the maximum nitrification rate and period of delay through nonlinear regression analysis have nitrogen, temperature and its coupling effect, and temperature effect reached significant level.2. Research of soil physicochemical properties change rule and its dynamic characteristics under the coupling condition of different fertilizer and temperature.(1)When the urea applied into soil, the overall trend of soil pH value is rised with the rise of nitrogen application and temperature in the first place, then it is decreased with the rise of nitrogen application and temperature when reaching a peak. Soil cultured under different conditions, its pH values are reduced by different degrees, where in the pH values decline largest under the condition of high temperature and high nitrogen application, through 15 days cultured, it is decreased about one unit; the pH values decline smallest under the condition of low temperature and low nitrogen application, through 55 days cultured, it is decreased about 0.4 units.The changes of soil pH values can be fitted well by the nonlinear dynamics model under the fertilizer and temperature coupling condition, the rate constant that obtained from the model can be used to reflect the speed of soil pH values change process under the fertilizer and temperature coupling conditions.(2)The overall trend of soil electrical conductivity is rised with the increasing of treatment time, finally leveled off and reaching a stable value.The relationship between soil electrical conductivity and treatment time can be fitted well by the S curve kinetics model under the fertilizer and temperature coupling condition, and it can be obtained an approximate steady state value asvEc. Factors of affecting the approximate steady state value through nonlinear regression analysis have nitrogen、temperature and its coupling effect.(3)By analyzing the correlation between soil nitrate nitrogen content and multi-factor under the coupling condition of different fertilizer and temperature, we can see: soil nitrate nitrogen content and soil pH, soil pH and soil electrical conductivity were negatively correlated, that is with the increasing of pH values, nitrate nitrogen content and electrical conductivity values decreased. With the increasing of soil electrical conductivity values, nitrate nitrogen content increased, nitrate nitrogen content and electrical conductivity values were a significant positive correlation and reached a significant level.3. BP neural network model of soil nitrate nitrogen content under the coupling condition of fertilizer and temperature.Based on the change features of soil nitrate nitrogen content under the coupling condition of fertilizer and temperature, we established three BP artificial neural network model(BP-NI, BP-NII and BP-NIII)with soil initial pH, soil initial electrical conductivity, temperature, fertilizer and time for input variables, with soil nitrate nitrogen content for output variables. And the models are trained and tested respectively. Results showed that the BP-NI and BP-NII model’s prediction accuracy of soil nitrate content reaching the target precision. But combined the larger workload of measure soil pH and soil conductivity values.In last we choose the BP-NII model to predict soil nitrate nitrogen content. |
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