Annual Overall Optimization Of Water And Nitrogen In Wheat-maize Rotation System In Western Guanzhong

The Guanzhong Plain is an important grain producing area in China.The production of winter wheat and summer maize has long faced key problems such as drought yield reduction,low water and nitrogen use efficiency and high fertiliser cost.In this study,we first conducted a field experiment to investigate the effects of irrigation and N application on the growth,yield and water and N use of winter wheat-summer maize.Then,the DSSAT model is calibrated and verified by using the field measured data,and the simulation accuracy of the model is evaluated.On this basis,the DSSAT model was used to simulate a continuous 30-year winter wheat-summer maize crop rotation with different annual nitrogen application treatments to quantify the effects of different nitrogen application schedule on winter wheat-summer maize yield,water and nitrogen use efficiency,and to propose a suitable annual nitrogen fertilizer system for the Guanzhong region.Finally,the DSSAT model was combined with a genetic algorithm to establish an irrigation optimization model for the winter wheat-summer maize rotation system,and to propose an irrigation system for winter wheat-summer maize under different meteorological years in the Guanzhong region.The results are as follows:（1）Irrigation and N application had significant effects on the growth and yield of winter wheat-summer maize.Analysis of the measured data showed that both growth and yield of winter wheat-summer maize reached their highest levels with twice irrigations and 216 kg ha^-1 N application.Under all irrigation conditions,the annual total yield was the highest when the annual nitrogen application ratio of winter wheat-summer maize was 5:5,while there was no significant difference between the annual nitrogen application ratio of 4:6 and this treatment.（2）Irrigation significantly increased total evapotranspiration from winter wheat-summer maize fields.However,increased N application did not significantly affect ET at the same irrigation level.Both irrigation and N application affected the nitrate-N content and distribution in the soil profile.The increase of irrigation and precipitation will promote the downward movement of soil nitrate-N.Under the same level of irrigation,the maximum soil nitrate-N residue was positively correlated with the amount of N applied.The response of water and nitrogen use efficiency（WUE,NUE）to irrigation and N application in winter wheat-summer maize was as follows:WUE was negatively correlated with irrigation and NUE was positively correlated with irrigation when the amount of N was applied.When the amount of irrigation was constant,WUE was positively correlated with N application,while NUE was negatively correlated with N application.（3）The DSSAT model is calibrated and verified by using the measured data.The results show that the model can accurately simulate the growth process,yield and soil moisture changes of winter wheat-summer maize after parameter localization.In order to determine a reasonable overall plan of nitrogen fertilizer,using the meteorological data of 30 consecutive years from October 1990 to September 2020,and based on the determined model parameters,the DSSAT-sequence model was used to simulate the yield,WUE and NUE of winter wheat-summer maize rotation.The results showed that the annual nitrogen application rate was 360kg ha^-1 and the nitrogen application ratio was 4:6,which was the best nitrogen application schedule in this area.（4）The nitrogen application plan was used to optimise the winter wheat-summer maize irrigation system under different meteorological year.The results showed that the irrigation amount of winter wheat in wet year,general water year and dry year were 75-150 mm,150-225 mm and 225 mm respectively.The irrigation in wet year was mainly in greening stage and jointing stage.The irrigation in general water year was mainly in overwintering stage,greening stage and jointing stage.The irrigation in dry year was mainly in overwintering stage,jointing stage and booting stage.Summer maize can be irrigated twice at most in the growth period.that the irrigation amount of summer maize in wet year,general water year and dry year were0-75 mm,0-150 mm and 75-150 mm respectively.mainly in jointing stage and tasseling stage.The annual irrigation and nitrogen fertilizer scheme can provide a reference for sustainable production and efficient use of water and nitrogen in winter wheat and summer maize in the Guanzhong Plain.It should be pointed out that due to the epidemic situation and time constraints,there are relatively few field trials,and the laws of nitrogen residue,utilization and transport are not clear enough.At the same time,only the single crop test data are used to calibrate and verify the DSSAT model,and the accuracy of the parameters needs to be further explored.