Soil Pore Size and Geometry as a Result of Aggregate - Size Distribution and Chemical Composition

SOIL pore space and its intrinsic characteristics such as surface area, roughness, tortuosity, and connectivity are probably the most important factors controlling water and solute movement in soils. Interaggregate porosity is the result of the arrangement of the soil aggregates. These aggregates are composed of subunits, of which clay minerals and other colloids are the main components. The way in which clay minerals and colloids arrange themselves determines the size and shape of the soil aggregates. Colloids are chemically and biologically very active, and this activity has been attributed to their high surface area and to the electric field surrounding the particles (Goldberg et al., 1999). The equilibrium distance between clays is the result of the forces caused by the electric field around the individual platelets, which results in a nonrandom arrangement of the particles in the soil. Properties at the mineral interface, together with the amount of water in the soil, control the type and strength of the association between particles. This self-arrangement is affected by chemical characteristics of the bulk solution, such as electrical conductivity (EC), type of cation, and pH. In situations such as the reclamation of sodic soils or the use of drainage water for irrigation, the soil texture remains constant, but its chemical composition changes with time. Changes in chemical composition affect the size and stability of the aggregates and, consequently, the hydraulic properties of the soil. In order to model the chemically induced changes in hydraulic properties, we need to have an understanding of the processes involved. We also need a methodology that allows us to measure the stability of aggregates having varying chemical compositions.Traditional methodologies to quantify the aggregate stability are based on measuring the size of the TECHNICAL ARTICLES