Effect of subsoiling on soil physical properties and pasture production ona Pallic Soil in Southland, New Zealand

This three-year study examined the effects on soil physical properties and ryegrass-white clover pasture production of subsoiling in a Pukemutu silt f oam (Pallic Soil). A range of soil physical properties were measured in 6-c m incremental depths to 30 cm. Subsoiling loosened the topsoil by pulling c onventional tines and winged tines, 50 cm apart through the soil at a depth of 25-30 cm. Subsoiling increased macroporosity by up to 27% of the soil v olume, and increased saturated hydraulic conductivity and air permeability by up to two orders of magnitude. Improvements in soil physical conditions were evident up to 2.5 years after subsoiling at 18-24 cm, although recompa ction and settling had occurred in the upper 18 cm of the soil profile. For the majority of the trial, there was no significant improvement in pasture production in subsoiled treatments. Pasture dry matter was significantly r educed (by 39%) during a dry summer period following winged subsoiling, mai nly due to moisture stress.