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

Abstract

The aim of this study was to describe quantitatively the effect of vehicular traffic on pore size distribution (PSD) of topsoil (0.05–0.15m) and subsoil (0.25–0.35m) aggregates (3mm and 8mm) 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, >1–3μm at 0.05–0.15m depth, and >0.3–0.4μm at 0.25–0.35m decreased with increasing soil compaction, mostly from NC to MC. At 0.25–0.35m depth this decrease was accompanied by an increase in the volume of smaller pores (<0.3μm) mostly from MC to SC. As a consequence, the volume of pores retaining plant available water (0.1–15μm radius) decreased in compacted soil. The differential pore curves exhibited peaks at the pore throat radius of 1–6μm. At 0.05–0.15m depth the peaks under SC were lower than under NC and MC, whereas at 0.25–0.35m depth they were lower under MC and SC than NC. At all compaction treatments and aggregate fractions the volume of larger pores >1–3μm was greater at 0.05–0.15m depth than at 0.25–0.35m depth and the inverse was true for smaller pores (<0.3μm). The observed changes in pore size distribution in the subsoil are considered as almost irreversible and thus long-lasting or even permanent.