Regulation Of Water Infiltration In Black Soil Based On Particles Interaction Forces

The black soil region of Northeast Chian is an important commodity grain producing area in China,which is of great significance to the food security in China.However,with the rapid increase of China’s population,in order to meet the people’s demand for food,the black soil area has been unreasonably exploited and utilized,while the conservation of the black soil has been neglected.As a result,the soil structure in this area has been seriously damaged,the content of organic matter decreased significantly,the thickness of the black soil become thinner,and the soil degradation is serious.As an excellent structure of soil,the stability of aggregates can not only represent the good degree of soil structure,but also be an important factor affecting water infiltration.Studies have shown that the interaction forces between soil particles,including electrostatic repulsion,van der Waals attraction and hydration repulsion,have important effects on the stability of soil aggregates.A large number of fine particles will be released after the aggregates are broken,which will block the channel of soil water migration,thus affecting the soil water infiltration process.However,there are few studies on black soil water infiltration from the perspective of soil particle interactions.In order to investigate the influence of the interaction forces between different particles on the water infiltration process of typical black soil in Northeast China,two types of typical black soil in Northeast China（Binxian and Keshan black soil）were selected as the research objects.The surface electrochemical properties of black soil in two regions were determined by the joint determination method of material surface properties,and the interaction between soil particles under different ion systems and electrolyte concentrations was quantified by theoretical calculation.The response mechanism of the typical black soil hydraulics characteristics to the particle interaction forces in Northeast China was clarified.Our results provide some theoretical reference for further scientific and efficient regulation of soil water infiltration characteristics in this region.The main findings of the study are as follows:（1）The magnitude and distribution of surface electric field and interaction forces between black soil particles under different ion systems and electrolyte concentrations were quantified.The results showed that the cationic exchange capacity and specific surface area of the black soil in Binxian and Keshan were 21.3 and 23.4cmol/kg,58.6and 66.5m²/g,respectively.Based on the classical double electric layer theory,the magnitude and distribution of the surface electric field,the electrostatic repulsion between particles,the van der Waals attraction and the hydration repulsion of the two black soils under the KCl and Ca Cl₂ systems were calculated,respectively.The theoretical results showed that the surface potential（absolute value）,electric field intensity,electrostatic repulsive force and net force of the two kinds of black soil all increased with the decrease of the electrolyte concentration of the bulk solution,and the changing trend of were similar,which increased rapidly at first and then kept stable gradually.The interaction between soil particles decreased sharply with the increase of the distance between soil particles.In the KCl system,when the electrolyte concentration decreased from 1mol/L to 0.001mol/L,the electrostatic repulsive force increased from 0.87atm to 18.67atm,and the net force increased from-5.23atm（attraction）to 12.57 atm.These results indicate that under natural conditions,when rain water or irrigation water enters the soil,due to the decrease of electrolyte concentration in soil bulk solution,the repulsion between soil particles will be sharply enhanced,and then the breaking intensity of soil aggregates will increase,leading to the destruction of soil structure.（2）The influence of soil particle interaction on water infiltration process of typical black soils were tested.By changing electrolyte concentration and ion types,we regulated the interaction between soil particles quantitatively;the aggregate stability and water infiltration characteristics of two black soils under different internal forces were studied.The experimental results showed that with the decrease of electrolyte concentration,the aggregate stability of the two soils decreased.At the same time,0.01mol/L is the key concentration of aggregate breaking.Taking Keshan black soil in the KCl system as an example.When the electrolyte concentration decreased from 1 to0.001mol/L,the cumulative infiltration amount decreased from 16.50g to 3.06g.These results indicate that the increased soil internal forces could increase the aggregate breaking strength and the release of fine particles which can block the pores of water migration,finally reducing the migration rates of wetting front,infiltration rate and cumulative infiltration amount.In the KCl system,the average water infiltration rate,stable water infiltration rate and average water infiltration rate decreased first and then keep stable.（3）The response mechanism of soil moisture characteristic curve and soil shrinkage characteristics to soil internal forces was revealed.By quantitatively regulating the interaction between soil particles,the variation trends of saturated hydraulic conductivity,soil water holding capacity and dry-shrinkage cracking of two black soils under different internal forces were studied.The results showed that under different black soil and ion systems,with the decrease of electrolyte concentration,the internal forces of soil particles increased,the soil saturated water conductivity decreased,and the water holding capacity increased.In the KCl system,taking the black soil of Binxian County as an example,when the electrolyte concentration decreased from 0.1 to 0.0001mol/L,the saturated hydraulic conductivity decreased from 0.03 to0.01mm/min.In the KCl system,the shrinkage of soil increased with the decrease of electrolyte concentration.With the decrease of electrolyte concentration,the characteristics of dry-shrinkage cracking generally increased.In Ca Cl₂ system,the contractility decreased with the decrease of electrolyte concentration.The characteristics of dry shrinkage cracking were not obvious with electrolyte concentration.