Effect Of Sand-incorporation Into Saline Soil On Water Infiltration And Salt Leaching In The Yellow River Delta

The Yellow River Delta was formed by the interaction of Yellow River alluvial sediments and marine sediments(Xia et al.,2019),the special process of land formation made the soil have the characteristics of compact structure,high bulk density and poor permeability,which eventually lead to the difficulty of salt leaching.Hence,how to solve low soil permeability is the key to improve the efficiency of salt leaching and saline soil reclamation.This experiment took the saline soil of the Yellow River Delta as research object,conducted indoor soil infiltration and salt leaching experiments by using one-dimensional vertical constant head ponding infiltration method,researched the effects of different sand-incorporation rates(0%,20%,50%)on the infiltration process,water and salt vertical distribution characteristics and salt leaching of saline soil under three kinds of soil particle size(<1 mm,1-2 mm,2-5 mm).The results of infiltration experiment showed that the cumulative infiltration amount and wetting front of different treatments increased with the increase of time,but its increased gradient was gradually slowed down,the cumulative infiltration amount and wetting front changed linearly with time after a certain duration.The cumulative infiltration and wetting front increase with the increase of sand-incorporation rate within the same time.In the process of infiltration,there was a linear relationship between cumulative infiltration amount and wetting front,and the gradient of cumulative infiltration amount changed with wetting front decreased with the increase of sand-incorporation rate.At the beginning of infiltration,the soil infiltration rates of different treatments were high and decreased rapidly,but their decline rate were gradually slowed down with time and eventually the infiltration rate approached to steady.Sand-incorporation could significantly improve soil infiltration performance,both the initial and stable soil infiltration rates increased with the increase of sand-incorporation rate.Although the second infiltration process was slower than the first infiltration process due to the increase of soil water content,sand-incorporation could still significantly increase the infiltration rate.The Kostiakov model and the Philip model were used to fit the infiltration data during the two infiltration processes.After comprehensive analysis,it was concluded that the Kostiakov model can more accurately describe the infiltration process of soil incorporated sand.By analyzing the vertical distribution characteristics of soil water and salt after the infiltration experiment,it was found that the water content of upper soil in each treatment was basically steady,and the water content of lower soil decreased with the increase of soil depth.Sand-incorporation reduced the water absorption and water holding capacity of soil,and the field capacity of soil after fully drainage decreased with the increase of sand-incorporation rate.The relationship between the field capacity of soil and sand-incorporation rate was linearly fitted,the fitting determination coefficient R²was greater than 0.98,which resulted in a linear model for estimating the field capacity of soil incorporated sand.The salt content of upper soil in each treatment was very low,but it increased with the increase of soil depth,and reached a peak at the wetting front.Sand-incorporation could significantly increase the desalination depth of soil and the desalination rate of the same soil layer.The results of salt leaching experiment showed that the speed of salt leaching was slow when the soil without sand-incorporation,sand-incorporation could effectively accelerate the speed of salt leaching,shorten the leaching time,and increase the amount of salt leaching per unit time.During the salt leaching process,the electrical conductivity of leaching solution was very high at the beginning of salt leaching but it declined quickly,and finally its value was basically steady.The fitting result showed that there was a good power function relationship between the electrical conductivity of leaching solution and the volume of leaching solution.After salt leaching,the desalination rate of K⁺in each treatment was between 50%-60%,the desalination rate of Cl-was the highest can exceed 98%,and the desalination rates of other ions were basically greater than 80%.Sand-incorporation rate had no significant effect on the desalination rate of K⁺,Mg²⁺and Cl^-after leaching,but the desalination rates of Na⁺and Ca²⁺increased with the increase of sand-incorporation rate,the desalination rate of SO₄^2-and the salt accumulation degree of HCO₃^-declined with the increase of sand-incorporation rate.The electrical conductivity of soil layer in different treatments all reduced to a lower value,and the electrical conductivity of the same soil layer decreased with the increase of sand-incorporation rate.Sand-incorporation could significantly reduce the SAR of soil.The more the sand-incorporation rate,the lower the SAR of soil after salt leaching,and the less harmful Na⁺was to soil.The pH of soil increased significantly after leaching,which lead to the alkalization of soil,but the higher the sand-incorporation rate,the less the increase degree of pH,sand-incorporation could inhibit the alkalization of soil.In summary,sand-incorporation could significantly improve soil permeability,accelerated soil salt leaching,and created a good soil environment for crop growth.The results can provide a scientific basis for the reclamation of saline soil in the Yellow River Delta.