Properties of fine-textured subsoils as affected by high axle load traffic

The direct effect of high axle load traffic on subsoil physical properties was investigated in two field experiments on fine-textured mineral soils (Vertic Cambisol). A clay loam was compacted to a depth of 0.40-0.35 m by a tandem axle load of 21 Mg and a silt soil to a depth of 0.50 m by a single axle load of 11 Mg, increasing the dry bulk density, penetrometer resistance and homogeneity of the subsoils and reducing their macroporosity (>300 and 30 mu m). In the silt subsoil, compaction also reduced the saturated hydraulic conductivity and number of cylindrical pores (>1 mm). Despite compaction, the subsoils with a good natural structure appeared to be able to maintain their structure moderately well.