| Hetao Irrigation Area in Inner Mongolia is located in arid and semi-arid area,which is the main grain and oil production base of China.The main crops in the irrigation area are corn,sunflower and wheat.The crops are distributed in flower arrangement patches.The growth of typical crops is represented by normalized difference vegetation index(NDVI),and the distribution of crop growth is complex.The soil and water environment in irrigation area is very important for crop growth.It is of great significance to master the relationship between soil and water environmental factors and crop NDVI and determine the optimal irrigation schedule in irrigation area.Water saving is an essential research goal of irrigation area,and irrigation amount is a key factor of water and soil environment,so the optimization of irrigation schedule is particularly important.At present,there are few studies on the relationship between NDVI and soil and water environmental factors in agricultural planting areas.It is worth to study the evolution relationship between crop growth and soil water environment and the optimization of irrigation schedule in arid and semi-arid irrigation area.In this thesis,we use remote sensing to extract NDVI time series curves of different crop types in irrigation area,establish decision tree,divide the planting structure of irrigation area,and analyze the growth characteristics of typical crops such as sunflower,corn,wheat and melon;The temporal and spatial variation characteristics of water and soil environmental factors in irrigation area were analyzed by using classical statistics and Kriging interpolation method;The coupling coordination degree model of crop soil water environment system was constructed to analyze the coupling coordination relationship between NDVI and soil water environment factors;The distributed hydrological model(soil and water assessment tool)is used in plain irrigation area.The problems of extracting fracture and end canal system in plain irrigation area are solved by improving the accuracy of DEM grid pixel,FORTRAN coding method of grid pixel value and predetermined sub basin and river network method.The simulation study area is determined by predetermined sub basin and river network method,Adding groundwater recharge term ET_k solves the key problem of insufficient groundwater recharge to soil water in shallow and deep irrigation area.The distributed hydrological model of Hetao irrigation area is constructed.The improved SWAT model is combined with the optimized crop water model in Hetao irrigation area to seek the optimal irrigation schedule.The main research results are as follows:(1)The change trend of NDVI in different crop structure and growth period was obtained by RS and GIS:the change of sunflower,corn,wheat and melon in their growth period was different with different crop phenological characteristics.The NDVI value of sunflower began to increase at seedling stage(mid June),and then the growth trend changed significantly;The NDVI value of maize began to increase at jointing stage(after the middle of May),and then the growth trend changed significantly;The NDVI value of wheat began to increase at tillering stage(mid April),and then the growth trend changed significantly;The NDVI value of cucurbits began to increase at the seedling stage(middle of May),and then increased significantly.(2)On the basis of regional monitoring,the change characteristics of soil water and salt in crop planting area were obtained by geostatistics method:soil water in crop planting area was excessive in regional scale(“??>67.31%”)in the whole growth period.From the end of July to August,water deficit area appeared due to evaporation and crop water consumption.The largest mild salinization area appeared in early May and mid June,and affected by surface evaporation and crop water consumption,the salinization classification was the most obvious in this period.The distribution of groundwater depth is shallow in the West and deep in the East,and the depth of well irrigation area is relatively large,ranging from 3.05 m to 6.5 M.(3)The coupling coordination degree model of NDVI and water and soil environmental factors is constructed.The coupling degree model is mainly used to describe the degree of interaction between two or more systems or elements,and to determine the degree of synergy between different types of crop growth and water and soil environmental factors in irrigation area.Its advantage is that it can reflect the interaction intensity and contribution degree of regional crop soil environment groundwater climate through the degree of mutual influence of coupling elements.The method to enhance the coupling and coordination between them is proposed.The annual changes of crop growth and soil and water environmental factors are closely related to the development process of growth period.The time series characteristics of the coupling degree between NDVI and soil and water environmental factors in the experimental year showed fluctuation and stability.The coupling and coordination relationship between fluctuating crop growth NDVI and soil and water environmental factors is mainly antagonistic,but not benign coupling,which needs to be further improved.The coupling coordination relationship between NDVI and soil and water environmental factors is mainly benign coupling,which indicates that soil and water environment and crop growth develop harmoniously.(4)The SWAT model established in plain irrigation area was improved,and the crop irrigation schedule was optimized by combining SWAT model with crop water model.It solves the problems of extracting fracture of SWAT model canal(river network)and insufficient extraction of end canal system in plain irrigation area.Adding groundwater recharge term to SWAT model makes up for the deficiency of the model in describing phreatic water evaporation in shallow groundwater irrigation area.Finally,the accuracy coefficients of the model runoff rate are R2:0.85,NS:0.73,pbias:-24,and the accuracy coefficients of the validation period are R2:0.67,NS:0.67,pbias:-2.6,which meet the basic requirements of the model simulation.The results show that the improved SWAT model can better simulate the actual evapotranspiration ET in Jiefang sluice irrigation area,and solve the problem that the accuracy of the model is not enough.It can optimize the irrigation schedule of irrigation area.Finally,the optimal irrigation schedule under the current conditions was obtained.The results showed that the optimal irrigation schedule for sunflower was 130 mm before sowing in normal water year,high water year and low water year,80 mm in water allocation time 5 days in advance of budding stage,and no irrigation in flowering and filling stage.The optimal irrigation schedule for maize was 90 mm in jointing stage,83 mm in trumpet stage,90 mm in tasseling stage and 75 mm in filling stage in wet and dry years.The irrigation treatment is the same as that in wet year and dry year.Minhas model is the best corn crop water model.The optimal irrigation schedule for wheat was 90 mm at tillering stage,82.5 mm at jointing stage and 90 mm at filling stage in dry and wet years.The water allocation time was 5 days ahead of the heading date in the normal year,and the irrigation treatment was the same as that in the dry year and the wet year.Minhas model is the best crop water model for wheat. |
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