Irrigation And Nitrogen Management For Winter Wheat-summer Maize In Guanzhong Region Based On AquaCrop Model

Winter wheat and summer maize are the two most important grain crops in Guanzhong area.Aiming at the shortage of water resources and low water and fertilizer use efficiency in the area.Based on field experiments,the effects of soil water content,leaf area index,aboveground biomass accumulation,yield,water use efficiency and partial productivity of nitrogen fertilizer in winter wheat and summer maize under different water and nitrogen conditions on were studied in this paper.At the same time,the meteorological data,soil data and field management data were collected,and the parameters of AquaCrop model were calibrated based on the measured data of winter wheat-summer maize,then the accuracy of model simulation of winter wheat-summer maize growth and development was evaluated.Finally,using Pearson III frequency curve to divide the typical annual precipitation of winter wheat and summer maize in their respective growth seasons,then the validated model was used to simulate different irrigation and nitrogen application schemes and the simulation results were evaluated.The water and nitrogen combination measures for maintaining high yield in Guanzhong Plain were further discussed.The main research results are given as follows:（1）Under the conditions of this experiment,irrigation and nitrogen application had different effects on growth,yield,biomass,water use efficiency and partial productivity of nitrogen fertilizer of winter wheat-summer maize.For winter wheat,the plant height and leaf area of winter wheat did not increase significantly when irrigation amount exceeds 80 mm and nitrogen application exceeds 180 kg·hm^-2.In wet years,80 mm irrigation and 220kg·hm^-2 nitrogen application is recommended.In normal years,the amount of nitrogen application should be reduced appropriately.100 mm irrigation and 180 kg·hm^-2 nitrogen application is recommended.this will not only save nitrogen fertilizer,but also achieve high yield;For summer maize,the plant height and leaf area of maize no longer increase significantly or even be restrained when the irrigation amount exceeds 60 mm and the nitrogen application exceeds 180 kg·hm^-2.In wet years,60 mm irrigation and 240 kg·hm^-2nitrogen application is recommended.In normal years,the amount of nitrogen application should be reduced appropriately,60 mm irrigation and 180 kg·hm^-2 nitrogen application can save water and fertilizer and achieve high yield.（2）The calibrated AquaCrop model can accurately simulate the growth process,yield and final biomass of winter wheat and summer maize.For winter wheat,the coefficient of determination（R²）and root mean square error（RMSE）between the simulated and observed values of canopy cover were 0.963 and 9.41%,the R² and RMSE between the simulated and observed values of aboveground biomass accumulation were 0.985 and 0.9 t.hm^-2.The simulation value of final biomass and yield simulation value are slightly higher in calibration process and slightly lower in validation process,there is a good consistency between yield and final biomass.For summer maize,the R² and RMSE between the simulated and measured value of canopy cover were 0.868 and 11.83%,and the R² and RMSE between simulated and measured of aboveground biomass accumulation processes were 0.975 and0.97 t.hm^-2.The simulated values of final biomass and yield are slightly higher in the calibration process and slightly lower in the validation process,there is a good consistency between yield and final biomass.Whether it is winter wheat or summer maize,the model can basically reflect the changing trend of soil water content during the growth period,although there will be a slight overestimation or underestimation.At the same time,the simulation error becomes larger when water or nitrogen stress occurs.（3）The simulation results of different precipitation typical years show that,for winter wheat,the optimal irrigation and nitrogen application schemes are as follows:220 kg·hm^-2nitrogen and 60 mm of irrigation water at turning green or jointing stage is recommended in wet year;220 kg·hm^-22 nitrogen and 60 mm of irrigation water at jointing stage is recommended in normal year;180 kg·hm^-2 nitrogen and 60 mm irrigation at turning green and jointing stage is recommended in dry year.For summer maize,240 kg·hm^-22 nitrogen and45 mm of irrigation water at jointing stage or tasseling stage is recommended in wet year;240 kg·hm^-22 nitrogen and 60 mm of irrigation water at jointing stage is recommended in normal year;180 kg·hm^-2 nitrogen and 60 mm irrigation at jointing stage and tasseling stage is recommended in dry year.The optimized irrigation and nitrogen application scheme can achieve the purpose of saving resources,high and stable yield,and it can provide reference for the actual production in Guanzhong area.In this paper,there may be some uncertainties due to the manual parameter adjustment method.The optimization algorithm will be applied to the parameter adjustment process to improve the efficiency and simulation accuracy.At the same time,the AquaCrop model is validated and applied in a single test area,it is necessary to set up more test areas in Guanzhong area,then a database will be set up to optimize regional irrigation schedule.