| Northwest China is a typical arid and semi-arid region.The shortage of agricultural water resources and irrational application of chemical fertilizer are important factors restricting the sustainable development of agricultural production.In order to improve the management level of agricultural water resources and water use efficiency,it is necessary to establish a set of scientific and reasonable evaluation system of agricultural water use and its environmental impact.The crop production water footprint achieves a unified evaluation of agricultural water use efficiency and concomitant effects,opening up a new perspective for agricultural water management.This study,taking Fengjiashan irrigation district as the research object,constructs a quantitative model of water footprint in the district,and analyzed the spatio-temporal evolution of water footprint of three major crops,and reveals the responding characteristics of crop water footprint to different management methods.On this basis,the best crop planting management method in the irrigation district was selected on the basis of water use efficiency,economic benefits and environmental impacts,and the regulation path of the water footprint of crop production in the Fengjiashan irrigation district was clarified.This study can provide a basis and reference for the efficient use and sustainable development of agricultural water resources in Fengjiashan irrigation district.The main results of this study are as follows:(1)A quantitative method of crop water footprint in Fengjiashan irrigation district was established based on APEX model.The basic data of Fengjiashan irrigated district was collected,and the model was calibrated and verified to realize the distributed simulation of water footprint of crop production in the irrigated district.The results showed that for the calibration period,the R~2 and RMSE for ET simulated and measured values were 0.81 and18.27 mm,respectively,and the R~2 for simulated and measured values of wheat,maize and rape yields were 0.84,0.86 and 0.83,respectively,and the RMSE were 0.23 t/ha,0.31 t/ha and 0.18 t/ha,respectively;for the validation period,the R~2 and RMSE for ET simulated and measured values were 0.70 and 15.59 mm,respectively,and the R~2 for simulated and measured values of wheat,maize and rape yields were 0.75,0.79 and 0.76,respectively,and the RMSE were 0.39 t/ha,0.43 t/ha and 0.28 t/ha,respectively.The simulated and measured values of ET and crop yield both agree well,which proves that the model can effectively carry out water footprint simulation studies in Fengjiashan irrigation district.(2)Based on the constructed quantitative water footprint model,the spatial and temporal distribution patterns of water footprints of three major crops(wheat,maize and rapeseed)in the irrigation district were analyzed.The spatial distribution of wheat water footprint was higher in central and western regions and lower in eastern regions;in terms of time distribution,the maximum value appeared in 2017,while the minimum value of water footprint mainly appeared in 2020.The spatial distribution of maize water footprint was low in the middle and high on both sides.the maximum value was distributed from 2016 to 2018,while the minimum value was mainly distributed in 2015 and 2018.The spatial distribution of rapeseed water footprint was higher in the east and lower in the west;in terms of the time distribution of rape water footprint,the maximum value was distributed from 2016 to 2018,and the minimum value was mainly distributed in 2020.(3)Based on the scenario analysis method,the response characteristics of crop production water footprint to irrigation water and fertilizer application in Fengjiashan irrigation district were revealed.Overall,the response of the blue-green water footprint of crop production to irrigation water showed a trend of increasing and then decreasing with the increase of irrigation water,and the blue-green water footprint of rapeseed was the most sensitive to irrigation water,with a maximum variation of 12.3%under different irrigation scenarios.The response of crop blue-green water footprint to fertilizer application showed an overall trend of decreasing and then increasing with the increase of fertilizer application,and the blue-green water footprint of wheat was the most sensitive to the change of fertilizer application,with the largest change of 27.6%.The gray water footprint of crop production showed an overall decreasing trend with increasing irrigation water,and the gray water footprint of rapeseed was the most sensitive to the change of irrigation water,with the maximum change of 13.2%under different irrigation scenarios.The response of crop production gray water footprint to fertilizer application was extremely obvious,and the crop production gray water footprint was more sensitive and stable to the change of fertilizer application,and the change of gray water footprint ranged from 18%to 23%when the fertilizer application scenario changed step by step.(4)Taking water use efficiency,economic benefits and environmental impacts into account,the optimal crop planting management method and planting system in the irrigation district were preferentially selected,and the regulation path of the water footprint of crop production in the Fengjiashan irrigation district was clarified.The results showed that among all scenarios,the scenario with a 10%increase in irrigation water and a 25%reduction in fertilizer application compared to the status quo was the optimal scenario.The optimization increased the area of wheat,corn and rapeseed monocultures and corn replanted with rapeseed,and reduced the area of wheat replanted with corn;by crop,the total planted area of wheat decreased by 12.7%;the total planted area of corn decreased by 13.9%;and the planted area of rapeseed increased by 78.5%.There was a significant reduction in the total water footprint of the irrigation district after optimization:for the whole irrigation district,the total blue water footprint decreased by 12.3%,the total green water footprint increased by 9.2%,and the total gray water footprint had a significant reduction,all in the range of18～19%.The net benefit of the optimization increased by 4.3%. |
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