Influence Of Irrigation Amount And Buried Depth Of Underground Pipe On Law Of Drainage And Salt Discharge And Numerical Simulation

Object:Northwest China is a dry area,with severe water shortage and prominent soil salinization.At the end of the 20th century,after the large-scale promotion of drip irrigation under film in Xinjiang,the original drainage channels were gradually abandoned,forming a"drip irrigation without drainage"mode.This model can moisten the root layer in the short term and make the root layer desalt temporarily,but it will aggravate the secondary salinization of soil in Xinjiang region in the long term,which will seriously affect the sustainable development of agriculture and environment in the region.Underground pipe drainage is an important means to control soil salinization,of which irrigation amount and buried depth of underground pipes are two important factors affecting the efficiency of drainage and salt discharge.Methods:Therefore,based on pipe drainage model test and HYDRUS numerical model,this paper determined the optimal combination of underground pipe depth and irrigation amount optimized by single index,established saline wasteland numerical model of the 146nd State Farm in Xinjiang by using the optimized numerical model parameters after verifying the numerical model.Results:This paper studied the influence of underground pipe depth and irrigation amount on water and salt transport law in various soil layers of farmland,and determined the optimal control scheme.Conclusions:?1?The soil column test used regression equation to determine the optimal combination of irrigation amount and buried depth of underground pipe corresponding to each response variable.Among them,under D60W42.96 treatment,the average desalinization rate of 0⁶0cm reached the maximum,83.15%;Under D73.88W42.45 treatment,the average desalinization rate of 0⁸0cm reached the maximum,78.74%;Under D80.41W42.96 treatment,0¹00cm average desalination rate reached the maximum,77.28%;Under D100W45 treatment,the salt discharge rate of the underground pipe reached the maximum,30.65%;Under D96.73W45 treatment,the salt discharge rate of underground water reached the maximum,50.76%.?2?Under the influence of pipe drainage,the soil column and soil bin desalinize significantly in each soil layer.The simulated values obtained by HYDRUS software were in good agreement with the measured values.The maximum RMSE value and minimum R² value of soil column moisture content were 1.677%and0.857 respectively,and the maximum RMSE value and minimum R² value of salt content were 1.720 g·kg^-1and 0.865 respectively.The maximum RMSE value and minimum R² value of soil bin moisture content were0.972%and 0.731 respectively,and the maximum RMSE value and the minimum R² value of salt content were 0.205 g·kg^-1 and 0.729 respectively,which were within the acceptable range.?3?The numerical model was used to simulate the saline wasteland in 146nd State Farm in Xinjiang.The results showed that with the increase of irrigation amount,the degree of soil desalinization became greater and greater.With the increase of buried depth of underground pipes,the effect of soil desalinization became better and better,but the buried depth of underground pipes had little influence on the average salt content of soil.The desalinization rate was the highest in the depth range of 0²00 cm under the treatment of buried depth of 2.2 m and irrigation quota of 480 m³·mu^-1,which was the best combination of irrigation amount and buried depth of buried pipe.The desalinization rates under the mulch and the whole reached51.72%and 16.67%respectively.?4?With the increase of the horizontal distance from the underground pipe,the soil moisture content and salt content of each layer have almost the same change trend except for some slight changes in numerical values,which indicates that the horizontal distance from the underground pipe has less influence on the salt transport of each layer of soil under the condition of deep buried underground pipe.