Simulation Of Water And Salt Migration And Optimization Of Irrigation System Under Water-Saving And Salt-Controlling Conditions In Sandy Farmland In Hetao Irrigation Area,Inner Mongolia

The shortage of water resources in the Yellow River has affected grain production and agricultural development in hetao irrigation area.Water saving and salt control have become the main concerns of agricultural sustainable development in the irrigation area.Sand intercalation is a common soil structure in northwest China,and also a basic soil structure in the alluvial plain.In this study,the law of soil water and salt movement and the law of crop water utilization were explored through the process of water and salt migration and the response of crop growth to soil with sand layer,and the influence of farmland with sand layer on crop growth and soil salinization control under the condition of water saving and salt control.Field experiments in 2020 and 2021 were carried out to monitor the changes of water salinity and crop growth in sand-covered fields during spring maize growth period.Hydrus-1d was used to simulate evapotranspiration,crop water use,water supply and seepage in deep soil,and salt transport in sandy soil.CROPWAT model was used to simulate the process of water movement in sand-embedded farmland under different irrigation intervals to find a feasible way to optimize the irrigation system.The main research contents and conclusions are as follows:1)The experimental observation showed that soil moisture was mainly distributed at the upper and lower boundaries of the sand layer during the growth period of maize,and the change rate of EC value was the highest in shallow sand layer and 7.90%in deep sand layer.When the thickness of the sand layer was larger in the root zone,it was beneficial to prevent the accumulation of salt to the soil surface.Soil moisture showed moderate variability in 0-40 cm soil depth,while soil total salt content showed moderate variability in maize root zone.Compared with the treatment with sand sandwiched soil,the treatment without sand sandwiched soil had a higher desalting rate after irrigation in the growing period of maize.2)The observation and analysis of crop growth indexes showed that LAI value of maize under shallow sand burial was greatly affected by irrigation quota,maize plant height was positively correlated with sand burial depth,and maize yield and 100-grain weight increased significantly with sand burial depth increasing(P<0.05).With the increase of sand buried depth,dry matter accumulation increased by 48.86%and 6.46%,respectively;with the decrease of sand thickness,dry matter accumulation increased by18.31%and 34.04%,respectively.The results showed that the stress on crop growth and yield decreased with the increase of sand depth.At the same time,the yield was greatly affected by the interannual climate change,and the grain yield and 100-grain weight of maize in dry year decreased by 31.08%and 30.66%,respectively,compared with that in normal year.3)The water productivity of maize increased with the increase of sand buried depth,and the water productivity of maize under deep sand buried treatment increased by 20.27%and 4.28%,respectively,compared with that under shallow sand buried treatment.With the increase of irrigation quota,maize water productivity decreased by 18.95%and 21.79%in normal water year,and increased by 27.33%and 15.21%in dry water year,respectively.When the irrigation amount was 315.85 mm,the soil water productivity decreased the least.4)HYDRUS-1D simulation showed that the water recharge from the capillary tube in the field without sand inclusion was 57.01%and 118.53%larger than that in the shallow sand inclusion and deep sand inclusion treatments,respectively.When the irrigation amount was 315.85 mm,the soil water seepage in the deep layer was the lowest.With the increase of irrigation quota,water deep leakage increased obviously,accounting for 19.5%and 26.6%of the total rainfall and irrigation,respectively.By reducing each irrigation quota,this irrigation system can reduce the loss of water from deep seepage by 20.4%to37.6%.5)HYDRUS-1D simulation shows that the ratio of E_a to ET_a in 2020 and 2021 is39.3%and 49.6%,respectively,and the ratio of actual and potential root water absorption is 65.4%and 61.9%,respectively,indicating that soil water evaporation loss under local field management system is relatively large.The root water absorption increased with the increase of sand buried depth,and the root water absorption without sand embedded layer was the least under water stress.The root water absorption of shallow buried sand layer and deep buried sand layer was 55.51%and 61.31%of the potential evapotranspiration,respectively,and that of the treatment without sand layer was 66.69%.The results can provide theoretical guidance for the establishment of irrigation system for farmland with sand inclusion in Hetao irrigation area.