Simulation Of Water And Salt Transport Under Different Winter Irrigation Scenarios In Yinbei Irrigation District

Ningxia Yinbei irrigation area is located in the middle temperate arid zone with arid climate,scarce rainfall,high wind speed,sand and dust,sufficient sunshine,strong evaporation,and frequent land salinization,which mostly manifests as salt frost and salt spot.In this paper,we study the water-salt transport characteristics of winter irrigation in Yinbei Irrigation District,Ningxia under the joint action of soil,water and salt,and develop a simulation model of water-salt transport in winter irrigation in Yinbei Irrigation District,Ningxia based on the coupling of irrigation water and soil type to reveal the law of winter water-salt transport in Yinbei Irrigation District and then guide winter irrigation in the district.In this study,we set up two soil types,sandy loam and sandy loam,900m3/hm2,1600m3/hm2 and 2800m3/hm2,and combined with Hydrus-1D model to explore the water-salt transport law under different irrigation water and soil types,and mainly obtained the following conclusions:(1)In the vertical soil column tests of different soil types,water and salt migrated fast in sandy soils and slow in sandy loam soils.For sandy soils,water and salt mainly accumulated in the 50-80cm depth soil layer when the winter irrigation quota was 900m3/hm2;when the winter irrigation quota was 1600m3/hm2 and 2800m3/hm2,water mainly accumulated in the 50-70cm depth soil layer and the soil column was desalinated.For sandy loam soil,when the winter irrigation quota is 900m3/hm2,water mainly accumulates in the 0-25cm depth soil layer and salt mainly accumulates in the 35cm depth soil layer;when the winter irrigation quota is 1600m3/hm2,water and salt mainly accumulate in the soil layer near 50cm depth;when the winter irrigation quota is 2800m3/hm2,the soil layer has high water content and salt mainly accumulates in the 50-70cm depth soil layer.The winter irrigation quota of 1600m3/hm2 can meet the requirement of salt compression and moisture conservation in heavily salinized sandy loam soil.The soil layer of sandy loam is completely desalinated from 0-80 cm depth.(2)The freeze-thaw process has an effect on salt transport,and the different settings of freeze-thaw duration will affect the final distribution of salt,the closer to the surface,the more obvious the effect of freeze-thaw on salt redistribution.However,after experiencing the freeze-thaw action,the salt content will not change drastically,and the conductivity curves of soil layers at each depth are basically flattened and deformed in the horizontal direction,and basically recover the initial conductivity values after the thawing is completed.(3)In the soil column test at the horizontal junction of different soil types,the migration rate of the wetting front in the sandy soil layer at the horizontal junction becomes slower compared with the sandy soil;compared with the sandy loam soil,the migration rate of the wetting front in the sandy loam soil at the horizontal junction is faster,and the migration of water salts in the sandy soil and the sandy loam soil at the horizontal junction is not synchronized.For the sandy loam at the horizontal junction,the 900m3/hm2 and 1600m3/hm2 winter irrigation quotas caused water to accumulate near 50cm and 50-80cm depth soil layers,respectively,and caused salt to accumulate in the 35-80cm and 50-80cm depth soil layers,respectively;the 2800m3/hm2 winter irrigation quotas caused water content to increase in all depth soil layers and desalinated the soil column at the same time.For the sandy loam soil at the horizontal junction,all three winter irrigation quotas increased the water content of the entire sandy loam layer.900m3/hm2 and 1600m3/hm2 winter irrigation quotas caused water to accumulate in the 35-50cm and 50-70cm depths,respectively.However,all three winter irrigation quotas caused the salt to accumulate starting at 15cm depth,and the serious depth of salt accumulation was 15-35cm,35-50cm and 50-70cm soil layer respectively.For the soil type with junction of sandy soil and sandy loam in horizontal direction,irrigation water will be discharged through sandy soil layer in priority,accompanied by side seepage phenomenon,and weaken the desalination effect of sandy soil and sandy loam at the same time,so that diffuse irrigation cannot achieve the ideal desalination effect and will cause water waste,therefore,depending on the actual soil distribution,it is recommended to take the necessary measures to minimize the water-salt exchange between the two at the soil junction.(4)The simulated water content of sandy soil and sandy loam soil in the vertical direction under different winter irrigation quotas is more accurate with time,and the simulated values can better reflect the actual water content.The accuracy of the simulation of the variation of vertical salinity of sandy soil and sandy loam with time under different winter irrigation quotas is high,and the simulated values can better reflect the actual salinity distribution.the Hydrus-1D model can better reflect the actual situation in the study area after parameter adjustment and accuracy check,and can be used to provide theoretical support for winter irrigation in the field.