Simulation Of Wheat Growth And Development Process Based On The CERES-Wheat Model

Crop model is an important tool in the process of agricultural production.It can simulate the growth of crops under different water conditions and the characteristics of crop response to water to some extent,but there are still some deficiencies.In this study,wheat was taken as the research target,and the observation data from Yangling experimental station in semi-arid and semi humid area of Northwest China were used to evaluate the simulation ability of the CERES(Crop Environment Resource Synthesis)-Wheat model under different water conditions.At the same time,the data were used to analyze the impact of model parameter uncertainty and water stress parameterization scheme on the model output,establish and validate the response mechanism of winter wheat phenology to water stress,build and validate a new leaf area index model,and compare different leaf area index schemes with different water use efficiency levels in the long term simulations.The main conclusions are as follows:(1)Simulation evaluation of the CERES-Wheat model under different soil moisture conditionsThe CERES-Wheat model was used to simulate different drought treatments in two consecutive growing seasons of winter wheat.By evaluating phenological stages(flowering and maturity),leaf area index(LAI),aboveground biomass,soil water content and yield,it was found that CERES-Wheat did not consider the effect of water stress in the simulation of phenology,and its simulation results were the same as those under full irrigation.The simulations of LAI,biomass,and yield were poor,and those variables even could not be truly simulated under the condition of full irrigation.The simulated deviation of water stress is caused by the unrealistic water stress parameterization.(2)Impact of parameter uncertainty and water stress parameterization on wheat growth simulationThe impact of parameter uncertainty and water stress parameterization on wheat growth simulation were analyzed.The results showed that under water stress conditions,the parameters calibrated by GLUE(generalized likelihood uncertainty estimation)method were significantly different from the observed values.Without considering the water stress scheme,the calibrated parameters using GLUE are in good agreement with the observed values,which further indicates that the defect exists in the water stress parameterization.Therefore,the unreal parameterization of water stress seriously affects the location of calibration parameters by glue algorithm.In addition,parameter sensitivity analysis showed that the model errors caused by water stress parameterization were mainly compensated by the most sensitive parameters for winter wheat growth and yield simulation,such as grain size and leaf heat spacing.Therefore,special attention should be paid to these parameters to identify possible structural defects of the model.In addition,the analysis of the impact of parameter uncertainty on the model output shows that the phenology related simulation can capture the observed results better when using multiple sets of parameters with and without considering water stress schemes.For yield,maximum leaf area index and final aboveground biomass,due to unrealistic water stress parameterization,the deviation of the model without considering water stress scheme is usually less than that under considering water stress scheme.(3)Optimization of the response mechanism of winter wheat phenology under water stress conditionsWe modified the relatively complete response mechanism of winter wheat phenology to different soil water conditions,and optimized the corresponding response function.That is,with the decrease of relative soil water content,the growth rate of winter wheat would first accelerate,then decelerate and finally stop,and the process is continuous.The results showed that the new method can accurately predict the changes of winter wheat phenology caused by soil water stress.The optimized response mechanism can more reasonably explain the effect of soil water stress on the winter wheat phenology.(4)Development of a new leaf area index schemeAccording to the correlation between the relative growth rate of leaf area index and the relative growth rate of crops,a new leaf area index scheme was established.The effect of leaf nitrogen content was considered in this scheme,because only a certain amount of nitrogen content existed in the leaves,a certain amount of carbohydrate could be synthesized.The weight of nitrogen also accounted for a certain proportion in the leaves,which should not be ignored.The scheme was coupled into the CERES-Wheat model,and the biomass scheme of the original model was also modified by adding the leaf nitrogen content.The new scheme performed well on simulating leaf area index,biomass and yield.The new leaf area index scheme can simulate leaf area index directly and have fewer parameters,which increases the applicability of the model.(5)Comparison of water use efficiency under different leaf area index schemesDifferent crop models have established different leaf area index schemes,which are placed in the same framework to simulate the yield and water use efficiency.Different schemes include CERES-Wheat,WOFOST,FASSET,STICS,DAISY and the new leaf area index schemes.The results show that all schemes can grasp the time series variation of yield,and the average value of multiple schemes performs the best.DAISY and WOFOST underestimated and overestimated the yield,respectively.WOFOST could always produce the maximum yield water use efficiency,which was related to the lower and higher cumulative leaf area index that they simulated respectively.For the mean value of multi-site long time series,the yield water use efficiency and plant water use efficiency of different schemes are generally opposite.The larger the cumulative leaf area index,the higher the yield,the higher the yield water use efficiency,the lower the plant water use efficiency,and vice versa.This study explored the wheat growth process by combining the experiment and model,and further improved the shortcomings of the model.The results of this study help to improve the explanatory level of the model,which has important theoretical and practical significance for the crop model application,and has a positive role in the construction of crop planting management decision-making system.