Analysis of Soil Textural Porosity Relative to Skeleton Particle Size, Using Mercury Porosimetry
1992
Fiès, J. C.
Soil textural porosity represents the pore space due to packing of soil particles. The characteristics of this pore space are affected by particle-size distribution. Binary mixtures of clay and skeleton (<2-µm and coarser particles, respectively) were studied to evaluate whether the textural-space division into clay-fabric pore space and its complementary space, lacunar pore space, could be modified by decreasing skeleton size. Skeleton particles with diameters of 400 µm (glass beads), 20, 13, 6, and 4 µm (silt) were mixed in the wet state with various clay contents (5–90%), then dried. Mercury porosimetry was used to characterize textural pore space by volumetric pore density distribution curves (VPD) and volumes intruded into small pores of diameter <0.05 µm (VSP). For clay-bead (400-µm) mixtures, bimodal VPD curves occurred for all clay-content levels, corresponding to distinct intrusion of either lacunar or clay-fabric pores. Values of VSP, however, were only related to intrusion into clay-fabric pore space. In clay-silt mixtures, unimodal VPD curves occurred, and VSP values were greater, when the clay content was >60 to 70%. Similarly, VSP values and the unimodal VPD curve were both explained by hidden lacunar pores, i.e., lacunar pores intruded only via clay-fabric pores. Clay-fabric pore space and lacunar pore space were always present in clay-silt mixtures, but the proportion of hidden lacunar pore space increased with clay content and at a greater rate the smaller the particle size.
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