Water And Salt Transport Between Farmland And Saline-alkaline Wasteland In Hetao Irrigation District And Farmland Salt Regulation

Hetao irrigation area is an important grain producing area in China.The shortage of water resources and salinization of soil are important factors that restrict the sustainable development of local agricultural economy.With the reduction of water diversion from the Yellow River and the implementation of various water-saving measures,it is very difficult for the soil salt in the irrigation area to be drained out of the area through irrigation,and most of it is transformed and transferred between cultivation and wasteland.Therefore,it is of great significance for improving the utilization rate of agricultural water resources and realizing the effective control of soil salt in the irrigation area to find out the distribution and transfer law of water and salt in cultivation wasteland in the irrigation area.From 2017 to 2018,this paper carried out the location monitoring test in the study area,and combined with local meteorology and groundwater depth,systematically analyzed the land use and water salt dynamics in the study area.Based on the scale of farmland,this paper studies the law of water and salt transport from farmland to wasteland in typical area,and uses grey relation and BP neural network model to quantitatively analyze the main factors that affect the salt content of arable wasteland.Taking sunflower farmland as the research object,a two-dimensional numerical model of water and salt in GSPAC system in typical area is constructed,which uses HYDRUS-2D to analyze the water and salt content in GSPAC system under different irrigation amount and groundwater depth in the research area In order to provide scientific basis for the regulation of water and salt balance in irrigation area and the regulation of water and salt in farmland,the appropriate irrigation system and groundwater depth were determined by numerical simulation.The main results are as follows:1.In the experimental area,the salt content of cultivated soil(0-40 cm)has a significant binary primary relationship with groundwater depth and mineralization,and the soil salt has a significant positive correlation with groundwater conductivity,but has a negative correlation with the burial depth.The determination coefficients of the regression equations of cultivated temporary wasteland are 0.5411,0.7406 and 0.7845,respectively=19.5791,81.4313 and 103.7307,indicating a good fit and significant regression equation.During the irrigation period,the soil moisture and salt content of cultivated land are greatly affected by irrigation,but with the passage of time,the soil moisture affected by evaporation gradually decreases and the phenomenon of returning salt appears.On the 2nd,5th and 8th day after irrigation,the soil water storage of 1 m cultivated land increased by 24.25%,2.64%and 0.36%respectively,and the soil salt storage decreased by 26.08%,20.03%and 15.17%,while the soil water content of critical land and wasteland in non irrigation area changed weakly in the same period.The critical wasteland is affected by the irrigation of cultivated land,the amount of soil salt storage increases,and the further away from the cultivated land,the salt accumulation rate of soil decreases gradually.Over time,salt return will occur in different types of land under evaporation.On the 2nd,5th and 8th day after irrigation,the salt storage of critical soil increased by 13.18%,14.71%and 14.87%respectively,while that of wasteland increased by 8.05%,9.32%and 9.64%respectively.2.By using grey correlation degree and BP neural network default factor sensitivity analysis,seven factors affecting the soil salt of cultivated wasteland were analyzed.The results showed that the two methods had the same ranking results.The main factors affecting the soil salt of cultivated wasteland were soil moisture content and soil evaporation.The correlation degree between the soil salt and water content of cultivated wasteland and wasteland was 0.76,0.73 and 0.75 respectively The sensitivity indexes of default factors of soil salt and water content were 2.67 and 2.16 respectively,and 2.08 and 2.48 respectively.At the same time,the self-test of default factor sensitivity index is completed.3.The water and salt balance of farmland and wasteland was determined by experiments.The water supply and discharge of farmland soil were 147.61 mm,90.25 mm and 62 mm,52.5 mm respectively in spring irrigation period.The water supply and discharge of farmland soil were 480.94 mm and 560.57 mm respectively in the irrigation process of crop growth period Mm,the soil water supply and discharge were 222.95 mm and 248.1 mm,respectively.The soil water was basically in balance.According to the analysis of salt balance in spring irrigation period,the salt accumulation in 2 m depth soil is 3.44 kg/mu,224.17 kg/mu,355.41 kg/mu and 614.94 kg/mu.4.Based on the current groundwater level and irrigation system,set different groundwater level and irrigation amount,and simulate the dynamic change of soil moisture content and salt content based on the hydraus-2d model.The simulation value is in good agreement with the measured value.Considering the influence of irrigation amount on soil water and salt transport and crop growth,a reasonable irrigation system and groundwater depth for effective salt washing and water use were developed.In 2017 and 2018,the appropriate irrigation amount was 85.5 mm and 82.8 mm respectively,and the corresponding optimal groundwater depth was 173.68 cm and 160.72 cm respectively.