Experimental Study On The Responses Of Infiltration And Salt Transport Of Saline Soil Incorporated With Sand To Irrigation And Leaching

The soil in the Yellow River Delta has dense structure,with poor permeability,and serious soil salinization.This area covers a large area and is an important reserve land resource in China.The importance of improving saline-alkali land is becoming increasingly prominent.Sand incorporating into soil is a widely used saline soil improvement measure worldwide,which can improve soil hydraulic conductivity.Irrigation and leaching are the commonly used methods in agricultural production of saline-alkali land,and the desalination effect is significantly.At present,the research is mainly focused on the leaching effect on soil salinity,but there are relatively few studies on the soil infiltration capacity change of saline soil after leaching desalination and remodeling.This study takes the coastal saline soil in the Yellow River Delta as the research object,through the soil being air-dried and broken after leaching,simulating the process of agricultural irrigation leaching and ploughing,to study the responses of saline soil infiltration and salt transport process to leaching and remodeling,under different sand content(0%,20%,50%)conditions.One-dimensional soil column infiltration tests were used to observe and record the advancing distances of the wetting front,calculate the infiltration rate,fit the soil water infiltration model,and measure the soil moisture content and electrical conductivity after irrigation infiltration and water redistribution.The relationship between the structure of soil aggregates,salt ions and soil infiltration capacity were analyzed in this study.The main results are as follows.(1).Effect mechanism of sand incorporating on saline soil infiltration and leaching remodeling was determined.The incorporation of sand into saline soil can improve the soil texture and soil infiltration performance.The wetting front movement velocity and infiltration rate increase with sand incorporating rate.Sand incorporating can increase the content of sand particles in the soil and increase the number of soil available pores,to accelerate the movement of water in the soil.At the same time,sand incorporating can accelerate the transport rate of salt from upper layer to deep soil,and the effect of sand incorporation on pressed salt and salt discharge of moderately saline soil is more obvious.In addition,soil remodeling caused by irrigation leaching reduced soil infiltration capacity.After leaching and remodeling,the infiltration capacity of moderate saline soil decreased significantly,and sand incorporating could reduce the decrease of infiltration capacity of moderate saline soil,while that of heavy saline soil was not obvious after leaching and remodeling.(2).Quantitative relationship of water holding capacity of saline soil to sand incorporating and leaching response was investigated.Sand incorporation leads to the decrease of soil water holding capacity and the proportional decrease of the field capacity,because of the lower specific surface area of sand particles,which affects soil water storage capacity.After leaching and remodeling treatment,the soil water holding capacity of moderate saline soil increased,the field capacity increased,and the water holding capacity of heavy saline soil also increased after leaching,but the change of field capacity was not significantly.(3).Responses mechanism of leaching remodeling soil infiltration to soil aggregate structure and salt ions content was revealed.Leaching and remodeling treatment destroyed the structure of aggregates in saline soil,decreased soil porosity and infiltration capacity.The stable infiltration rate was positively correlated with the content of macroaggregates and small and medium aggregates,significantly positively correlated with the content of microaggregates(p<0.05).Leaching treatment significantly reduced the salt ions content in saline soil(p<0.05),Na~+and Cl~-content,which had adverse effects on crop growth and development,decreased by85.7%to 99.8%,and sodium adsorption ratio(SAR)decreased by 63.9%to 96.9%.Sand incorporating has no significantly effect on the decrease of salt ions content in the leaching process.In the process of leaching,salt ions make the soil expand,which leads to the disintegration of soil aggregates and the blockage of macropores.Compared with the influence of sodium ions content and the change of SAR,changes in agglomerate structure dominate the effect on infiltration capacity.After leaching and remodeling treatment,the soil structure of saline soil with different sand incorporating rates changed,and the process of soil infiltration and salt transport was significantly different from that of saline soil.Philip and Kostiakov infiltration models can well simulate the process of water infiltration in this experiment.This study provides a reliable scientific basis for the infiltration performance of saline soil after irrigation and leaching,provides theoretical support and technical guidance for saline-alkali land improvement and sustainable land use,and has good research value and application prospects.