Study On Agricultural Water Saving Potential Of Gaotai County Of Zhangye City

In arid regions of China,where precipitation is scarce and evaporation is high,the contradiction between water supply and demand is serious.Agricultural water consumption is the main source of water resources shortage,and the utilization of agricultural water resources directly affects the development and evolution of the agroecosystem.Carrying out quantitative assessment and comprehensive evaluation research on agricultural water-saving potential in arid areas can not only provide a scientific basis for local agricultural development planning,but also provide reference for agricultural water-saving work in similar water-limited areas in Northwest China.In view of some problems existing in current agricultural water-saving potential research,such as the lack of consideration to the impact of climate,field management and soil moisture changes on the evapotranspiration in actual agricultural production activities and not reflecting the real water-saving issues.This paper takes Gaotai county of Zhangye City in Gansu Province,a typical arid area,as the research area to study agricultural water-saving potential.This research collected and sorted out the data of crops,climate,soil,and management in the research area from 2002 to 2015 to construct and calibrate AquaCrop model.Establish a multi-objective optimization model,use the linear weighting method and the global improved normalization method to solve,and calculate the water-saving potential of resource agriculture.The Lagrangian multiplier method is used to combine the improved AHP method and the entropy weight method to determine the comprehensive weight,and the gray correlation evaluation method is used to evaluate the agricultural water-saving potential.The main influencing factors and the exploration space of the agricultural water-saving potential of Gaotai county were clarified,and suggestions were provided for the development of local agricultural water-saving work.The key summaries are as follows:(1)The AquaCrop model was used to simulate the yields of the three main crops of seed maize,commodity corn and wheat in Gaotai county from 2002 to 2015.The results showed that the simulation accuracy of the three crop yields was good,and the rank of simulation accuracy was commodity corn>seed maize>wheat.The AquaCrop model with determined utilization rate was used to simulate soil water balance and calculate crop evapotranspiration.The annual evapotranspiration of seed maize,commodity corn and wheat simulated with AquaCrop model in Gaotai county from 2002 to 2015 were 351.7,393.1 and 433.3 mm,respectively,with Seed maize<commodity corn<wheat in descending order.Fitting the linear trend equation of evapotranspiration showed that the evapotranspiration of seed maize,commodity corn and wheat decreased by 1.59,1.24,and3.17 mm/year respectively from 2002 to 2015.(2)Based on the crop yield and soil moisture balance modeled with AquaCrop model,linear weighting and global improvement normalization methods,the goal of maximum yield and minimum evapotranspiration,the resource agriculture water-saving potential of Gaotai county have been obtained year by year.After the adjustment of soil moisture,the average annual evapotranspiration reductions of seed maize,commodity corn and wheat in Gaotai county from 2002 to 2015 were 8.0,13.4 and 14.6 mm,respectively,and the average annual resource water saving potential was 496.6,498.1 and 580.4 thousand m3,respectively.The average annual resource water saving potential of Gaotai county is 1.5751 million m3.There are two main factors restricting the water saving of resource agriculture in Gaotai county.First,the unreasonable irrigation water volume and irrigation methods have caused part of the deep water leakage and loss.Second,the expansion of planting area in recent years has consumed a lot of water resources.(3)A comprehensive evaluation index system for agricultural water-saving potential at the county level has been constructed.Based on the analysis of the connotation and characteristics of the comprehensive evaluation of agricultural water-saving potential and the principles of evaluation index system construction,a comprehensive evaluation index system of agricultural water-saving potential was constructed based on the principles of project water saving,technical water saving,economic water saving and management water saving.Project water saving includes 6 indicators: canal water utilization rate,field water utilization rate,field engineering matching rate,surface water irrigation rate,water-saving irrigation rate,and irrigation facility intact rate.Technical water saving includes 4 indicators: land leveling rate,good seed rate,coverage moisture retention rate,and farming moisture retention rate.Economic water saving includes 5 indicators:irrigation water supply cost,water price,irrigation water implementation water price,water fee collection rate,government efficient water-saving financial investment funds,and high water-consuming crop planting area ratio.Management water saving includes 3 indicators:crop irrigation quota,agricultural irrigation water measurement rate,and the number of farmers’ water use associations.(4)A comprehensive evaluation method of agricultural water-saving potential was established to evaluate the agricultural water-saving potential of Gaotai county in a typical year and propose the measures to tap agricultural water-saving potential.We calculated and sorted out the comprehensive evaluation index data of the agricultural water-saving potential of Gaotai county in 2002,2008 and 2015,adopted the improved AHP method and the entropy weight method to determine the comprehensive weight,and used the gray correlation evaluation method to evaluate the agriculture of Gaotai county Water saving potential.The evaluation results indicated that the year with the greatest agricultural water-saving potential in Gaotai county was 2002.The agricultural water-saving potential in 2008 was the smallest,and the agricultural water-saving potentials in 2008 and 2015 were similar.From 2002 to 2008,the agricultural water-saving work in Gaotai county has made great progress.From 2008 to 2015,the development of agricultural water-saving work has slowed down.There is still room for exploration of agricultural water saving in Gaotai county,including maintaining and repairing irrigation facilities,controlling the amount of groundwater extraction,rationally determining the cost of irrigation and water supply,and reducing the planting area of high water-consuming crops.