Study On The Effect Of Sand Incorporation Into Saline Soil On Soil Permeability And Soil Salt Leaching

The soil in the Yellow River Delta has the hydraulic characteristics of fine soil particles,uniform gradation,compact arrangement,and few large pores.The soil has great capacity,poor permeability,and high salt content,which easily causes serious soil salinization.It is difficult to improve the soil by traditional methods,and seriously threatens the growth of crops and food production safety.Sand mixing in saline soil can improve soil texture and structure,accelerate the disintegration of soil blocks,improve soil permeability,regulate the process of water and salt transport,and improve the efficiency of salt leaching.In this paper,the saline soil in the Yellow River Delta region is taken as the research object.The laboratory soil column simulation test is used to set three sand mixing ratios:CK（0%）,S1（20%）,S2（50%）.<1 mm（20%）,1～2 mm（28%）,2～5 mm（34%）,5～10 mm（18%）,the washing water was set as 3000 ml,and the experiment was repeated three times in each group.The influence of different sand mixing ratio on soil block disintegration,water and salt migration process and salt leaching efficiency of saline soil in two successive water infiltration processes was studied,to clarify the influence mechanism of sand mixing on the improvement effect of massive saline soil.Through the observation of the test process and the processing and analysis of the test data,the main results are as follows:（1）Sand mixing can improve the disintegration degree of saline clods.Before the test,in the soil obtained by wet screening method,the soil mass content of<0.25 mm was only 34.21%of that of dry sieve method.After the first water redistribution,the soil mass content of S1 and S2 was measured by two methods.Compared with the control group,the soil content of 0.25mm decreased by 17.92%and 51.45%.The content of clods with particle size>0.25 mm was relatively high in 0-5 cm soil layer,and decreased with the increase of soil depth.On the contrary,the content of soil clods with particle size<0.25 mm is relatively low in the surface layer and increases with the increase of soil depth.（2）Sand mixing can improve water infiltration efficiency and shorten infiltration duration.With the increase of sand mixing ratio,the infiltration duration of wetting front to the specified depth in different infiltration stages decreases continuously,and the particle size<0.25 mm clod is significantly lower than that of 5-10 mm clods,and the infiltration duration is proportional to the clods size.The wetting peak and cumulative infiltration continued to increase with the infiltration process,but the growth rate gradually decreased.At the same time,both the wetting front and cumulative infiltration showed S2>S1>CK.The change of infiltration rate over time was divided into three stages.The stable infiltration rate of S1 and S2 treatments increased by60.00%,66.67%and 400.00%,900.00%in the first and second infiltration process,respectively,compared with the control group.The desalting rate at the same depth is proportional to the proportion of sand mixing.The desalting depth of S2 treatment is 33.3%and 45.45%higher than that of S1 treatment and control group,and the desalting amount is 1.19%-19.01%and4.21%-77.52%higher than that of S1 treatment and control group,respectively.（3）Sand mixing speeds up leaching rate and reduces soil alkalinity.Compared with the control group,the time for the end of rinsing in S1 and S2 treatment was reduced by 31.63%and 79.15%,respectively.The change of the conductivity of leachate with time can be divided into three stages:fast decreasing,slow decreasing and tending to stability.According to the time when the conductivity of leachate tends to be stable,the ratio between the leaching depth and water height under the same cross section can be determined as 1:0.85-1:0.97.The p H value of leachate increases with the increase of sand mixing ratio and has a positive correlation with time.Sand mixing can improve the desalination rate by reducing the phenomenon of clogging pores after disintegrating.（4）Sand mixing can improve the efficiency of salt washing.The stripping rate of cation increases with the increase of sand mixing ratio,and the stripping rate of Na⁺and Mg²⁺is the highest,both above 95.00%.The stripping rate of Ca²⁺is low,ranging from 53.78%to 56.39%.When the sand mixing ratio is 50%,the stripping rate is the highest.The sodium adsorption ratio（SAR）of each treatment decreased with the increase of sand mixing ratio.Compared with the control group,the SAR value of S1 and S2 treatments decreased by 25.50%and 59.68%,respectively.Sand mixing in saline soil can not only directly reduce the soil salt,but also indirectly reduce the salt by increasing the stripping rate of cations in saline soil,and the more sand mixing,the better the salt washing efficiency.In conclusion,the soil blocks of sand-doped saline soil are easy to disintegrate under the condition of water infiltration,and the infiltration rate and salt leaching efficiency are significantly improved by increasing water conduction channels.The results can provide a basis for soil salinization amelioration mechanism and control method.