Effects Of Different Modifiers On Water Movement In Aeolian Soil

China has vast land,but the phenomenon of desertification is severe.It not only has a negative impact on the ecological environment,but also has an impact on social and economic development.Nowadays,the area of desertification land in China alone has reached over 2.6 million square kilometers.Due to the influence of natural factors and human factors,the soil structure in the desertification area has been seriously damaged,and the content of clay in the desert is very small,which leads to the extremely fast migration rate of water into the desert and the reduction of soil water holding capacity year by year.In order to address the issue of soil desertification,various technologies and methods for improving windblown sand soils such as sand fixation and control have been proposed worldwide.This includes effective measures such as physical sand fixation,chemical sand fixation,biological sand fixation,and joint sand fixation.Most of the previous research methods were single and isolated,and these research methods are far from sufficient for the improvement of the complex system of aeolian sandy soil.Therefore,in this experiment,various improvement materials were mixed and applied to the sandy soil to regulate the water movement of the sandy soil,improve its water retention,and thus improve the sandy soil in desert areas.This paper aims to study the effects of different application rates,application positions,and application thicknesses of single and mixed improvers on water movement in windblown sandy soil.A one-dimensional soil column vertical water infiltration experiment is conducted indoors.Salt soil,bentonite,organic matter（PAM,humus,biochar）and other five kinds of improved materials were selected.On the basis of effectively regulating the water movement of windblown sand soil with a single improved material,various improved materials are added to improve the water retention of windblown sand soil.This study set up multiple treatments,using windblown sand as the base and adding different proportions of improvement materials,to analyze the effects of the application amount,application location,and application thickness of mixed improvement agents on the water infiltration characteristics,water distribution,and water retention of windblown sand.After obtaining the optimal ratio,the mechanical composition,total nitrogen,total phosphorus,total potassium,p H value,and organic matter content of the experimental windblown sand soil were analyzed.The experimental results showed that:（1）The increase in the application amount of the same modifier will lead to a continuous decrease in the distance of the moist front movement in windblown sand soil.This indicates that saline soil,bentonite,and organic matter have a certain effect on reducing soil water infiltration.Among single modifiers,macromolecular organic matter PAM has the best inhibitory effect on water infiltration in sandy soil,and with the increase of PAM application amount,the inhibitory effect on water movement in sandy soil becomes more obvious;The inhibitory effected of bentonite Li⁺on water infiltration in sandy soil is stronger than that of bentonite and bentonite Na⁺.Among the mixed improvers,the mixed improver made by adding saline soil,bentonite,and PAM has the best inhibitory effect on the water movement of sandy soil.（2）The application position of different modifiers has different effects on the water movement of windblown sand soil.The closer the application position of the modifier is to the surface of the soil,the more significant the reduction in the transport distance of the wetting front.The mixed modifier 1%bentonite Li⁺+0.1%PAM+98.9%aeolian sand has the most significant impact on the wetting front transport distance,transport rate,and cumulative infiltration amount at different application positions.With the prolongation of water infiltration time,the difference in wetting front migration distance between different modifiers becomes smaller and smaller,and the migration rate gradually tends to 0.The different application positions of different modifiers can also affect the soil moisture content and water holding capacity.The soil moisture content above the layer application position is significantly higher than that below the application position.The water holding capacity of 5%saline soil+95%aeolian soil as an amendment is worse than other amendments when applied.Among all treatments,the mixed application of1%bentonite Li⁺+0.1%PAM+98.9%sandy soil resulted in the highest soil moisture content and the best water holding effect,with a water holding capacity of 0-30cm/total infiltration rate of over 90%.（3）Under the same modifier,as the application thickness increases,the distance of wetting front migration gradually decreases.At the same infiltration time,the thicker the soil layer with the application of amendments,the smaller the wetting front migration distance and infiltration rate.At the same time,the soil profile moisture contented is also affected by different proportions of mixed amendments and application thicknesses.At the same soil depth,the thicker the amendment is applied,the higher the moisture content contained in the soil layer.The application of different thicknesses has no significant effect on the water holding capacity of the 1%bentonite Li⁺+0.1%PAM+98.9%aeolian sand mixed improver,and the water holding rate can all reach over 90%.But for other treatments,there are significant changes:the thicker the modifier is applied,the higher the water retention rate and the stronger the water holding capacity.The water holding capacity of bentonite Li humus Ca²⁺/biocarbon Ca²⁺is significantly stronger than that of bentonite Li⁺humus/biocarbon as the application thickness becomes thicker.After analyzing the physicochemical and electrochemical properties of the mixed improver,it was found that the content of clay and powder particles in each improver increased,while the content of sand particles decreased.The addition of biochar Ca²⁺can increase the N and P content in soil;Humus can increase the content of organic matter in soil.The water retention of Ca²⁺saturated humus and biochar as improved materials is higher than that of natural humus and biochar.Based on comprehensive analysis,this study found that the strongest water retaining modifier for aeolian sandy soil is:1%bentonite Li⁺+0.1%PAM+98.9%aeolian sandy soil,with the optimal application location and thickness at 10-20 cm.The mixed modifier that can keep the water at the plough layer and better provide nutrients is 1%bentonite Li⁺+humus Ca²⁺+98%aeolian sandy soil.The best application position and thickness are 10-20 cm.