Establishing Soil Water-carbon-nitrogen Process And Crop Growth Joint Model And Its Application Of Water And Nitrogen Management

In China,the rapid increase of grain production in recent decades relies too much on water and fertilizer inputs,which not only increases the cost of grain production,but also enhances the risk of environmental pollution.Therefore,the quantitative description of soil water flow,carbon(C)and nitrogen(N)cycles,and crop growth processes at soil-plant-atmosphere continuum system is helpful for improving water and N use efficiencies and decision-making of crop production and environmental protection.Based on the previous research findings,a coupled model(Soil Water Heat Carbon and Nitrogen Simulation,WHCNS)model was established.The model integrated some features of several widely used crop and soil models,and some modifications were made in order to apply the WHCNS model under the complex conditions of intensive cropping systems in China.Then the field applicability of the WHCNS model was tested using several field experiments.The main research contents and results are as follows:The model runs on a daily time step.Soil water infiltration and redistribution processes are described by Green-Ampt and Richard's equations,respectively.Soil N transport simulation was based on the modified convection-dispersion equation.The source-sink term of N transformation and transport includes N mineralization-immobilization,urea hydrolysis,ammonia volatilization,nitrification,denitrification and crop uptake.The simulation of organic matter turnover was directly introduced by Daisy model from Denmark.The crop growth process was described either by the improved version of PS 123 or EPIC crop model.The WHCNS model was evaluated using an open access dataset and its simulated results was compared with other 14 soil-crop system models.The results showed that the WHCNS model performed better in simulation of soil water and N dynamics,dry matter accumulation and crop N uptake among these models.A model-independent optimization tools PEST(Parameter ESTimation)was fully coupled with WHCNS model to optimize soil hydraulic parameters,crop parameters and N transformation parameter and to conduct sensitivity.The PEST method not only greatly saved time for model calibration,but also achieved higher simulation accuracy than traditional methods.The sensitivity analysis results showed that soil water hydraulic parameters(soil saturated water content)and crop genetic parameters(the total accumulated temperature and maximum specific leaf area)were significantly higher than those of soil nitrogen transformation parameters.The results of global sensitivity analysis were similar with PEST results.Importantly,it showed that the greater the crop's water and N stress,the stronger the parameters interaction,with irrigation remaining the key factor.Nitrate contamination of groundwater is an environmental concern in the western Alxa oasis,Inner Mongolia,China,where this polluted groundwater is in turn used as a major irrigation water resource.The WHCNS model was adopt for water and N management in this area.The results indicated that WHCNS model performed well in modeling water and N fates,and summer maize growth under the irrigation with high nitrate water.The scenario analysis results showed that high yield and low nitrate leaching could be achieved when the irrigation frequency remains five times and the rate of irrigation about 105 mm for each event.The WHCNS model modified to simulate soil temperature,water content and rice growth under film mulching(FM)condition in the hilly region of Hubei Province in Central China,and compared with the orginial model.The results indicated that the modified model accurately simulated the changes in soil temperature,soil water content,LAI,dry matter and yield under FM condition.The modified model significantly improved simulation accuracy in the early crop growth.The scenario analysis suggested that the reduced irrigation with 80%field capacity and applying 75 kg urea N ha-1 plus 75 kg N ha-1 as manure can achieve "more yield with less water"A DRAINMOD-based drainage component was developed for the WHCNS model.The drainage-enhanced WHCNS performed well in simulating soil water storage,crop dry matter,crop N uptake,subsurface drainage and its associated N losses in a subsurface drained crop production system.And the performance of subsurface drainage and its associated N loss simulations becomes better with the increasing of time scale from daily to annual.Based on scenario analyses,an optimal N application rate ranging from 100 to 120 kg N ha-1 was commended to reduce subsurface drainage water nitrate concentrations to within the federal drinking water standard(<10 mg N L-1)while maintaining com yield.