Methods of increasing pasture growth on subsoil of a red-brown earth exposed by landforming

Abstract

Subsoils are often exposed during landforming for flood irrigation. Pasture growth on subsoil of red-brown earth soils is generally poor. Two ungrazed experiments were conducted on these soils to evaluate methods of increasing productivity of established pasture (experiment 1) and newly sown pasture (experiment 2) on areas of exposed subsoil. Pasture production, soil water status and soil strength were measured. In experiment 1, pasture yield was increased by more frequent irrigation and any soil modification which increased the intake or availability of water. During the irrigation season there was a positive response to applied nitrogen wherever soil water supply was increased. During the rainfed period pasture production was increased by soil modification, nitrogen and by high rates of phosphorus. Total annual yield was increased from 9.1 t/ha at district levels of input to 14.6 t/ha where inputs were maximised. The best yield was only 80% of published values for pasture production on undisturbed areas in the Goulburn Valley. In experiment 2, organic matter (50 t/ha) and replacement of topsoil (75 mm) increased yield by 17 and 47% respectively. However, the positive effect of organic matter on yield persisted for only 10 months after application. Topsoil replacement was the only treatment to restore pasture production to levels previously published.