Optimization Of Water And Nitrogen Management Of Winter Wheat Based On AquaCrop Model And UAV Remote Sensing

With the development of agriculture,the integration of information technology and modern agriculture is the inevitable trend of agricultural development.Accurate estimation of crop yield forecasting is of great significance for accurate field management,agricultural policy making and food security.In this study,different irrigation and fertilization rates of winter wheat were carried out in Shangshui County experimental base of Zhoukou City,Henan Province,and the field experiment data of different years were obtained.By analyzing the influence of AquaCrop model parameters on canopy coverage,biomass and yield,sensitivity parameters were determined,and field measured data were used to calibrate sensitive parameters,so as to obtain model localization parameters.Sensitivity analysis was performed to determine the effects of AquaCrop model parameters on canopy coverage,biomass and yield.According to the results of sensitivity analysis,the sensitive parameters were calibrated by field measurement data,so as to obtain the localization parameters of the model.Secondly,based on the localization of AquaCrop model,different simulation scenarios were set to analyze the effects of different water and nitrogen treatments on the yield and water use efficiency of winter wheat in different rainfall years.Finally,on the basis of the model sensitivity analysis results and model localization,the winter wheat canopy coverage and biomass retrieved from remote sensing data were used as state variables,and the least square method and AquaCrop model were used to carry out assimilation study,and the model simulation value and measured value of winter wheat yield after assimilation were analyzed.The main results of this study are as follows:(1)Sensitivity parameters and conservative parameters of the AquaCrop model were defined in this study.According to the results of sensitivity analysis,the sensitivity parameters of canopy coverage were determined as maximum canopy coverage,the days from seeding to maturity,the days from seeding to canopy senescence,and canopy growth coefficient.The sensitivity parameters of biomass were days from seeding to canopy senescence,standardized water productivity,days from seeding to maturity.The sensitivity parameters of yield were harvest index,days from seeding to canopy senescence,days from seeding to ripening,standardized water productivity.(2)The calibrated AquaCrop model can better simulate the growth process and yield of winter wheat.Under different water and nitrogen application levels,the R2,RMSE and d values of simulated and measured canopy coverage ranged from 0.84 to 0.98,4.8%-7.3% and 0.93-0.98 respectively.The R2,RMSE and d of simulated and measured biomass of winter wheat ranged from0.89 to 0.97,1.0 t/ha to 2.0 t/ha,and 0.96-0.99 respectively.The R2 and RMSE of simulated and measured grain yield were 0.90 and 2.86 t/ha respectively.(3)Based on 30 m uav multi-spectral images of winter wheat at greening stage,articulation stage,flowering stage and filling stage,this study analyzed the correlation between 23 vegetation indices and measured canopy coverage and biomass at four growth stages.According to the results of correlation analysis,the vegetation index with very significant correlation is selected to construct the inversion model.The results of showed that inversion and measured values of winter wheat canopy coverage and biomass during four growth period were based on the inversion model.The results of canopy cover such as R2 were 0.78,0.79,0.69,and 0.87 respectively.RMSE were 0.94%,1.97%,1.54% and 3.04% respectively.NRMSE were 2.49%,2.13%,1.60% and 3.46% respectively.The results of biomass such as R2 were 0.82,0.89,0.83 and 0.83,respectively.RMSE were 0.79 t/ha,8.71 t/ha,1.86 t/ha and 1.95 t/ha,and NRMSE were 15.10%,12.24%,16.67%,16.67%,14.99%,respectively.It can be seen that the inversion models constructed in different growth periods have better inversion effects and can be used to invert canopy coverage and biomass.(4)Based on sensitivity analysis results and localization of AquaCrop model,the model was assimilated with remote sensing data to estimate winter wheat yield.In this study,canopy coverage and biomass were used as state variables.The R2 and RMSE of the simulated value after assimilation were 0.83 and 4.21% respectively,and the R2 and RMSE of the simulated value after assimilation were 0.90 and 2.32 t/ha respectively.The R2 of measured value and assimilated value of winter wheat yield in different years were 0.82 and 0.80,respectively.AquaCrop model combined with remote sensing could be used to predict winter wheat yield.(5)The effects of different water and nitrogen application levels on winter wheat yield and water use efficiency in different rainfall years were analyzed using calibrated AquaCrop model.In wet years,the best irrigation scheme was no irrigation.In normal years,150 mm of irrigation water was applied at jointing stage and flowering stage.In dry years,225 mm of irrigation water was applied at jointing,flowering and grain-filling stage.