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

摘要：

土壤孔隙对土壤水分和养分迁移及水土保持有着关键作用，不同离子条件下土壤颗粒相互作用控制着土壤团聚体稳定性，而土壤团聚体形成和结构对土壤孔隙状况起重要影响。紫色土是三峡库区代表性土壤之一，探究离子特异性效应下颗粒的相互作用对紫色土孔隙状况的影响，对三峡库区水土生态环境安全具有重要意义。采用工业CT扫描技术和联合测定法分别对不同类型离子条件下的土壤孔隙状况和颗粒表面电荷性质进行测定，并分析其形成土壤孔隙特征差异原因。结果表明，（1）当浓度为0.01 mol·L^-1时，Cs⁺体系下土壤孔隙的数量分别是Li⁺、Na⁺和K⁺体系下的2.90、2.23和1.44倍，其中，Li⁺、Na⁺、K⁺和Cs⁺体系下>1 mm孔隙数量分别占0.33%、1.06%、1.57%和1.88%；同时，Cs⁺体系下土壤最大孔隙的直径分别是Li⁺、Na⁺、K⁺体系下的1.97、1.81、1.30倍。（2）当浓度为0.01 mol·L^-1时，Li⁺、Na⁺、K⁺、Cs⁺体系土体中>1 mm土壤孔隙体积占所有孔隙比例分别为22.7%、40.1%、56.5%、59.9%，并且，Cs⁺体系下土体中>1 mm土壤孔隙体积分别为Li⁺、Na⁺、K⁺体系的13.70、5.22、2.70倍；同时，土壤孔隙度在Li⁺、Na⁺、K⁺、Cs⁺体系下分别为1.36%、2.06%、2.84%、7.22%。（3）在测定孔隙相同离子浓度条件下，Li⁺、Na⁺、K⁺、Cs⁺体系中紫色土颗粒表面电位分别为-210.34、-198.63、-186.29、-175.57 mV，绝对值表现为Li⁺>Na⁺>K⁺>Cs⁺，进一步计算发现，在相同颗粒间距离3 nm时，Li⁺、Na⁺、K⁺、Cs⁺体系下颗粒间净作用力分别为4.68、3.90、2.32、-0.15 atm，同样表现为Li⁺>Na⁺>K⁺>Cs⁺。该研究表明Li⁺、Na⁺、K⁺、Cs⁺通过改变紫色土表面电荷性质，进而引起土壤颗粒间相互作用力发生变化，最终影响土壤的孔隙状况。

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