The soil structure profile under pastures

It has been found that under reconditioning pastures the soil develops a strongly differentiated structure profile within normal ploughing depth. Aggregation (2 mm) as measured by the wet sieving technique was, for short-term subterranean clover and ryegrass pastures, high at the surface but decreased rapidly with depth. In contrast to this, a more vigorous dispersion test showed that the crumbs of these highly aggregated surface layers broke down to give a greater amount of fine material (<50 µ) than did soil from below the old 3-in. cultivation depth. A demonstration of the practical implications was obtained on ploughing in a 3-year pasture. Chisel, mould board, and disc ploughs were used at three depth settings. Where the structure profile was inverted or mixed, infiltration rate and porosity were better maintained during a winter fallow than when the soil was loosened but not inverted.