Effects Of Cementing Substances On Pore Structure And Study Of Response Of Soil Properties To Acidification

Soil pore is an important factor affecting the soil structure,and it is also the transportation channel of water,nutrient and gas as well as the living space of animals,plants and microorganisms in the soil.Therefore,studying the relevant factors affecting the pore size distribution is important for agricultural production and environmental protection.Soil acidification is a worldwide environmental problem and it will lead to the degradation of the soil physical and chemical properties,endangering the sustainable development of ecological environment.Therefore,it is of practical significance to study the response process and mechanism of soil to acidification.This study focused on soil pore and soil response to acidification.The effects of different cementing agents on soil pore distribution were analyzed.The changes of soil physical and chemical properties during acidification were studied.The main results were as follows:1.Iron oxide and organic matter are the main cementing materials of soil structure in tropical and subtropical soils.The pore size distribution of soil is an important component of soil structure.The effects of iron oxide and organic matter on soil porosity and pore size distribution(PSD)were studied by comparing the difference before and after iron oxide and organic matter removal.Soil pore volumes of 0.37-100?m and 0.001-0.1 ?m were determined using mercury porosimetry(MIP)and nitrogen adsorption(NAI),respectively.Soil total pore volume and total porosity was significantly reduced after removal of iron oxide and organic matter.The removal of iron oxide showed the more obvious impact on pore structure than organic matter.Pore size distribution(PSD)analysis showed that removal of iron oxide and organic matter decreased significantly>75 ?m pore volume,while increased pore volume of<5 ?m.The pore size distribution of red soils is dominated by 5-0.1 ?m pore.The BET specific surface area and BJH pore volume of soil were determined by nitrogen adsorption method.The removal of iron oxide significantly reduced the BET specific surface area while the removal of organic matter could increase the BET specific surface area.The removal of iron oxide increased the pore content at 0.01-0.025 ?m and 0.025-0.05 ?m.In general,the effect of iron oxide on red soil porosity and size distribution was higher than that of organic matter.2.Multifractal theory can analyze the complexity and heterogeneity of soil pore distribution.The results showed that the removal of iron oxide and organic matter reduces the full width of the multifractal singular spectrum ??,which indicated that the iron oxide and organic matter can promote the complexity of pore size distribution.The iron oxide removal made the multifractal singular spectrum more slmetrical than organic matter removal,which indicated the effect of soil iron oxide on the heterogeneity of pore size distribution was significantly higher than that of organic matter.The information dimension Di and the correlation dimension D2 of soils with iron oxide and organic matter removal were significantly larger than that of the original soils,indicating that the removal of iron oxide and organic matter reduced the volume of the original pores with high content and increased the volume content of other pores,which meant concentration of the pore size distribution was reduced and the pore size distribution was more uniform.3.In order to study the response of soil to acidification,an electric simulation of soil acidification was used.After electric simulation acidification,the soil showed obvious pH gradient,the closer the soil was to the anode,the lower the pH value.The higher the original pH of the soil,the higher the pH dropped after acidification.The neutral paddy soils are most likely to be acidified.The closer the soil was to the anode,the higher the content of exchange acid content and SOM,the lower the content of exchangeable cation Ca`2+,exchangeable cation Mg`2+,exchangeable cation K+ and exchangeable cation Na+.The change of exchangeable Ca`2+ and exchangeable K+ were more obvious than the change of exchangeable acid.After simulating soil acidification,the lower pH soils have smaller compressive strength.However,there is not significant impact of acidification on the regularity of deformation in soils.The total pore content of the original soils did not determine the compressive strength of the soils after the electric simulation acidification.The compressive strength of soil was negatively correlated with exchangeable H+ concentration,exchangeable Al3+concentration,soil porosity and SOM;as well as positively correlated with soil pH,exchangeable Ca`2+ ion concentration,exchangeable Mg`2+ concentration exchangeable K+ concentration and exchangeable Na+ concentration.