关键词: 土壤孔隙, 相互作用力, CT扫描, 离子特异性效应, 联合测定法, 紫色土

Abstract:

Soil pore space plays a key role in soil water and nutrient migration and soil conservation. The interaction of soil particle under different ionic conditions controls the stability of soil aggregate, while the formation and structure of soil aggregate play an important role in soil pore conditions. Purple soil is one of the representative soils in the Three Gorges Reservoir area, and it is important to investigate the influence of particle interactions under ion-specific effects on the pore condition of purple soil for the ecological and environmental security of soil and water in the Three Gorges Reservoir area. Therefore, in this study, industrial CT scanning technique and combined measurement method were used to determine soil pore conditions and particle surface charge properties under different types of ionic conditions, and to analyze the reasons for their differences in forming soil pore characteristics. The results showed that (1) the number of soil pores in the Cs⁺ system was 2.90, 2.23 and 1.44 times higher than that in the Li⁺, Na⁺ and K⁺ systems at the concentration of 0.01 mol·L^-1, respectively, where the number of >1 mm pores accounted for 0.33%, 1.06%, 1.57% and 1.88% in the Li⁺, Na⁺, K⁺ and Cs⁺ systems, respectively. Meanwhile, the maximum pore diameter of the soil in Cs⁺ system was 1.97, 1.81 and 1.30 times higher than that in Li⁺, Na⁺ and K⁺ systems, respectively. (2) When the concentration was 0.01 mol·L^-1, the proportion of soil pore volume >1 mm in the soil of Li⁺, Na⁺, K⁺, Cs⁺ system to all pores was 22.7%, 40.1%, 56.5%, 59.9%, respectively. Moreover, the pore volume of soil >1 mm in the Cs⁺ system was 13.70, 5.22, and 2.70 times higher than that in the Li⁺, Na⁺, and K⁺ systems, respectively; meanwhile, the soil porosity was 1.36%, 2.06%, 2.84%, and 7.22% in the Li⁺, Na⁺, and K⁺, and Cs⁺ systems, respectively. (3) Under the same ion concentration conditions of the measured pores, the surface potentials of purple soil particles in Li⁺, Na⁺, K⁺, Cs⁺ systems were -210.34, -198.63, -186.29, -175.57 mV, and the absolute values followed the order: Li⁺>Na⁺>K⁺>Cs⁺. Further calculations showed that at the same interparticle distance of 3 nm, the net interparticle forces of Li⁺, Na⁺, K⁺, and Cs⁺ systems were 4.68, 3.90, 2.32, and -0.15 atm, respectively, and the same performance showed the order as follows: Li⁺>Na⁺>K⁺>Cs⁺. This study shows that Li⁺, Na⁺, K⁺, Cs⁺ change the pore condition of the soil by changing the charge properties of the purple soil surface, which in turn causes changes in the interaction forces between soil particles.

Key words: soil pore space, interaction forces, CT scan, ion-specific effects, combined assay, purple clay