Image analysis and three-dimensional modelling of pores in soil aggregates

Three cross-sections of soil aggregates (2–5 mm diameter) were digitized at 5 μm resolution from montages (× 100) of scanning electron micrographs to produce binary images representing the soil pores and soil matrix. A three-dimensional random Boolean process was chosen as a model of the soil pores and matrix. The soil matrix was simulated by randomly positioned, overlapping spheres with radii drawn from an exponential distribution. Simulation of a 1 mm cube of one soil aggregate showed that all but 0.1 % of the pore space was connected to the exterior, although only 50% appeared to be connected to the exterior in a cross-sectional image. Pore spaces able to accommodate different sizes of microorganisms were also investigated. For example, a protozoan with a cross-sectional diameter of 20 μm could be accommodated in 17% of the pores in a 1 mm³ soil cube, although only 11 % of the pores would be accessible to those protozoa on the exterior of the cube.