Estimating effects of compaction on pore size distribution of soil aggregates by mercury porosimeter

The aim of this study was to describe quantitatively the effect of vehicular traffic on pore size distribution (PSD) of topsoil (0.05–0.15 m) and subsoil (0.25–0.35 m) aggregates (3 mm and 8 mm) of silty loam. The treatments were: (NC) zero traffic, (MC) three passes, and (SC) five passes. Mercury porosimeter was used to determine the PSD. The PSD was presented in the form of cumulative pore volume and logarithmically differential pore volume curves vs. pore radius. The total aggregate porosity, average pore radius and volume of larger pores, > 1–3 μm at 0.05–0.15 m depth, and > 0.3–0.4 μm at 0.25–0.35 m decreased with increasing soil compaction, mostly from NC to MC. At 0.25–0.35 m depth this decrease was accompanied by an increase in the volume of smaller pores ( 1–3 μm was greater at 0.05–0.15 m depth than at 0.25–0.35 m depth and the inverse was true for smaller pores (< 0.3 μm). The observed changes in pore size distribution in the subsoil are considered as almost irreversible and thus long-lasting or even permanent.