| The Yanghe Watershed has become the"Beijing-Tianjin-Hebei"green agricultural and sideline product support base due to its local characteristic planting industry,and it is also the region with the highest utilization rate of water resources.The output value of agricultural planting in the basin occupies an absolute proportion in the local gross national product,and the proportion of water consumption is as high as more than 70%.Yanghe Watershed,as a typical north irrigation area in China,has a prominent problem of water shortage.According to statistics,in the past 20 years,the runoff of Yanghe Watershed main stream has been decreasing year by year,from 12 m~3/s to about 1 m~3/s.In order to ensure the economic benefits of Yanghe Watershed,under the condition that the total water supply in the basin is constant,the core is to improve the conversion rate of blue and green water,that is,to improve the utilization efficiency of planting water resources in the basin.The water footprint theory solves the quantification problem of blue and green water resources on the macroscopic scale and provides an effective quantification method for the study of water resource utilization efficiency in Yanghe Watershed.In this paper,based on the basic data and historical statistics of Yanghe Watershed in the early stage,the crop water footprint calculation model of Yanghe Watershed was constructed under the guidance of water footprint theory,and the spatial and temporal evolution rules of blue and green water footprints of various districts and counties in Yanghe Watershed from 2005 to 2016 were explored.The method of qualitative and quantitative analysis was used to explore the ways that meteorological factors,irrigation system and agricultural machinery automation affect the water footprint of crop production in Yanghe Watershed.By using numerical simulation method,the proportion range of blue and green water footprint was determined based on the results of research content 1,and as the constraint condition of research content 3,the optimization scheme of planting industry structure under the guarantee of planting output value and water satisfaction degree of Yanghe Watershed was put forward.The main conclusions are as follows:(1)The proportion of blue and green water footprint of five crops of maize,millet,flax seed,potato,tomato in eight districts and counties of Yanghe Watershed is 54:46?55:45?13:87?16:84 and 37:63,respectively.As the major food crops,maize and millet(73%),their blue water footprint is larger than that of green water footprint,which has a large space for optimization and adjustment.From 2005 to 2016,the blue and green water footprints of five crops in eight districts and counties of Yanghe Watershed generally showed a stable trend of decline.From the threshold range,the ratios of blue and green water footprints of corn,millet,flax seed,potato and tomato in each district and county were 0.13~0.97,1.23~2.23,2.13~8.53,3.87~10.08,1.54~5.41,respectively.From the perspective of time change,the blue and green water footprints of five crops in eight regions and counties of Yanghe Watershed from 2005 to 2016showed a trend of steady decline on the whole.From the perspective of spatial change,the blue and green water footprints of five crops in some regions and counties were significantly different in the years of high water,low water and low water.Quantification of crop water footprint can provide basic data for crop industry optimization and water footprint control threshold determination in Yanghe Watershed.(2)According to relevant analysis,it is concluded qualitatively that eight factors including temperature,wind speed,sunshine duration,humidity,agricultural machinery,rainfall,nitrogen fertilizer and phosphorus fertilizer are the main ways to affect the water footprint of crops in Yanghe Watershed.According to the results of qualitative analysis,the path and contribution rate analysis show that:Rainfall is the main route for crop water footprint,on the one hand,rainfall by humidity obvious negative effect on crop water footprint,on the other hand through the obvious negative effects on water footprint of nitrogen fertilization,the water footprint on crop production accounted for10.90%,shows that rainfall can directly affect crop green water resources quantity,change the blue and green water ratio which affect crop water footprint can appropriate amount indirectly affect crop fertilizer by humidity,water footprint,with rainfall size not by planting the optimization constraints are changed,thus improve the green water resource utilization can make full use of the positive role of water resource;In terms of input of agricultural means of production,fertilizer application and agricultural machinery all affect the water footprint of crops through interaction.(3)Based on the results of research content(1)and research content(2),five crops in eight districts and counties in the Yanghe Watershed in the year of abundant water were selected,and the total output value of crops in each district and county was guaranteed to be maximized.According to the optimized model,the areas of millet,corn,flax seed,tomato and potato were reduced by 18738 mu,247336 mu,21350 mu,11944mu and 40233 mu respectively.Reduced crop acreage although affect crop yield by increasing water use efficiency can increase crop yield per unit area to improve the comprehensive economic efficiency,the millet,corn,sesame seed,tomatoes,potatoes by surface water and groundwater irrigation,the optimal water 89.3%,88.9%,97.1%,81.5%,87%can effectively improve the utilization efficiency of water resources to achieve economic benefit optimization.Finally,by comparing the net income before and after the optimization of five crops in each district and county,it can be concluded that after the optimization and adjustment,the net income of each district and county increased by 504 million yuan,accounting for 1/5 of the net income before the optimization,indicating that the planting structure optimization program has achieved good economic benefits. |
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