| Henan Province is the main summer maize production region in China;however,the yield of maize in this region has been seriously threatened by seasonal water shortage.It is important to improve maize yield and stability by appropriate irrigation allied to high water-use efficiency(WUE).In this study,The Decision Support System for Agrotechnology Transfer(DSSAT)have been applied to determine the optimal irrigation schedules under different initial soil water conditions of summer maize in different hydrological years in the northern region of Henan Province.Two maize varieties,Yuan No.3 and Li Le 66,were calibrated and validated by using the summer maize phenological phases,above-ground biomass,and crop yield of summer maize,soil water content from 2016-2018 in Xun County and 2017-2018 in Wen County,respectively,by which to evaluate the performance of the DSSAT model in the North Henan.Subsequently,Based on the precipitation during summer maize growing season from 1988-2018,we used the P-III frequency curve method to define(typical)wet year,(typical)normal year and(typical)dry year,applied with three levels of initial water contents[40%DUL,60%DUL and 80%DUL referring to 50% field water capacity,60% FWC and 80% FWC].Finally,a calibrated model was used to simulate the effects of different irrigation treatments on the yield potential of summer maize for different initial soil water conditions in different hydrological years.Based on a database containing precipitation,temperature,solar radiation in maize growing period of 1988-2017,the potential photosynthetic thermal productivity and photosynthetic thermal precipitation productivity of summer maize were estimated and yield increase potential was analyzed.Based on different hydrological years and different initial soil content conditions,the water shortage during the summer maize growing season was estimated with different irrigation models.The optimal irrigation period was determined by comparing yield responses to different irrigation amounts and time,The optimal irrigation amount was determined by setting the irrigation amount level of summer maize during the key irrigation period and considering the yield and water use efficiency,thereby enabling optimization of the irrigation schedule with yield and WUE.The main findings from the research are as follows:The GLUE procedure together with normalized root mean square errors(n RMSE),root mean square errors(RMSE),and index of agreement(d)showed that good agreement and consistency were achieved between the simulated and measured value in both the calibration and validation periods.n RMSE of the above-ground biomass at the flowering stage of 2016 in Xun County and 2018 in Wen County were 15.05% and 16.89% respectively,the n RMSE of flowering stage,maturity stage,above-ground biomass at flowering stage and maturity stage and grain yield were all less than 10%.RMSE of the soil water content was less than 0.1,and the d value was more than 0.6.These results indicated that DSSAT model was applicable to in the north Henan province,and it can simulate summer maize yield,phenology,above-ground biomass and soil water dynamics correctly.The potential photosynthetic thermal productivity was 5742~15996 kg/hm2,and averaged 10727 kg/hm2,which can be used as reference value of average yield in irrigated fields.The potential photosynthetic thermal precipitation productivity was 821~14878 kg/hm2,and averaged 7088 kg/hm2,which accounted for a photosynthetic thermal productivity of 66% and can be used as the reference value of average maximum yield in rained fields.Water shortage during the summer maize growing season has varied significantly.When the initial soil water content was 50%DUL,the annual mean of water shortage was 125.1 mm,with a variation of 12.02 to 354.5 mm.When the initial soil water content was 60%DUL,the annual mean of water shortage was 101.1 mm,with a variation of 6.5 to 323.8 mm.When the initial soil water content was 70%DUL,the annual mean of water shortage was 73.3 mm,with a variation of 2.5 to 286.7 mm.Thus,the most suitable irrigation schedule should be chosen according to different initial soil water conditions in different hydrological years.The crucial irrigation period and the optimal irrigation amount of summer maize varied significantly over different hydrologic years under different initial soil water content conditions.The results showed that in wet years,when the initial soil water content was 50%DUL,irrigation of 20~30 mm at flowering stage should be applied;when the initial soil water content was 60%DUL and 70%DUL,irrigation was unnecessary.In normal years,when the initial soil water content was 50%DUL and 60%DUL,Irrigation of 50~180 mm and 50~120 mm at planting and Jointing or flowering stage should be applied;when the initial soil water content was 70%DUL,irrigation of 20~70 mm at flowering stage should be applied.In dry years,when the initial soil water content is 50%DUL,if planting stage was subjected to drought stress,irrigation of 160~280 mm at planting,and jointing,flowering or grain filling stage should be applied three times,otherwise,irrigation at jointing,flowering and grain filling stage should be applied;when the initial soil water content was 60%DUL,irrigation of 150~220 mm should be applied at flowering stage and jointing or grain filling stage twice or three times;when the initial soil water content was 70%DUL,irrigation of 140~180 mm at flowering stage and jointing or filling stage should be applied.The potential yield,water shortage and optimal irrigation amount responded differently among different summer maize varieties,while the crucial irrigation periods were basically identical.Under the optimized irrigation schedule,when WUE reached the highest level in wet,normal,and dry years,the yield obtained accounted for 95.26%,94.64% and 96.31% of the maximum yield,respectively.The optimized irrigation schedule would produce a higher summer maize yield with the highest WUE. |
