Study On Dynamic Simulation Of Soil Water And Salt Content In Irrigation Area In Oasis In The Lower Reaches Of Tarim River

In order to understand the dynamic change of salt contents in soil in the irrigation area in oasis in the lower reaches of the Tarim River and provide decision-making basis for production management,the author of this study collected the data of meteorology,soil,crops,groundwater,irrigation and drainage in the irrigation area through actual surveys and water and salt location monitoring,and combined with indoor measurement results,the soil salinity characteristics and spatial variability in different periods of the irrigation area were studied.From the perspective of optimizing reasonable irrigation and drainage,the SahysMod model was used to simulate and predict the dynamic changes of soil water and salt contents under different irrigation and drainage modes.The results showed:1.The soil in the study area was alkaline,and the soil salt content was significantly affected by the seasons.At different depths,the amounts of soil salt contents ranked in the following order:autumn>winter>spring>summer.Soil salt contents were characterized with sulfate dominantly in spring and autumn,and with chloride-sulfate in winter;the annual change of soil salinity in the irrigation area was characterized with salification in autumn and winter and desalination in spring and summer,and the salt content of soil in the root zone(0-60cm)in spring was higher in the northwest and lower in the southeast,which was contrary to distribution of soil salt content in deep layer(60-100cm).The soil salinity in summer was relatively low on the whole,and the horizontal distribution was more consistent.The areas of high soil salinity in autumn and winter all appeared in the southwest direction of the study area.2.After calibrating the model,the model sensitivity parameters were determined.The leaching efficiency Flr of cultivated land and wasteland root zone was set to 0.65 and 1,respectively.The leaching efficiency Fix of the transition layer was 0.9 and the aquifer washing efficiency Flq was 1;the verified SahysMod simulation presented a good simulation effect.The average value of the predicted salt value in the 0-100cm soil layer was in good agreement with the average value of the measured value.The mean square error(MSE)and root mean square error(RMSE)were well within the acceptable range,so that the SahysMod model could be applied to study the dynamics of water and salt in irrigation area.3.Under the current irrigation and drainage model,incoming ten years would witness increase of the salinity of the cultivated land and wasteland soil.The rate of increase would vary depending on the initial differences in salt contents.Increasing irrigation during the growth period and winter irrigation could reduce the soil salt content in autumn and spring,but the reduction was limited.When the winter irrigation amount was reduced by 14%under the current conditions,the soil salt content in spring was still at a level that could meet the need for growth of the crops.Therefore,the amount of salinity was recommended to decrease to 360 mm;the increase in salinity of irrigation water would increase the rate of salinity.Using 3g · L-1 of brackish water for irrigation would enable the soil salinity to reach the threshold after 2 years of continuous use.4.Under the condition that the total amount of water diversion remained unchanged,during the same period,the drainage volume would gradually increase with the increase of the canal utilization coefficient,and the degree of drainage mineralization would continue to decrease with the increase of the canal utilization coefficient.Under the circumstances where the irrigation quota remained unchanged,controlling the salinity of irrigation water,increasing the coefficient of canal system utilization,reducing the total water diversion,and controlling the input of salinity in the irrigation area would have a significant effect on alleviating the soil salinization problem in the irrigation area When the salinity of irrigation water was controlled at 0.4g · L-1 and the utilization coefficient of canal system was increased by 20%,the soil salt content of irrigation area would decrease slowly in the next 10 years,and the total amount of water diversion could be reduced by 16.67%.