Most soils used for agriculture in south-western Australia were acutely phosphorus (P) deficient when first cleared for agriculture. Native vegetation had evolved to cope with the very low P status of the soils but fertiliser P needed to be applied for profitable production of introduced crop and pasture species. When very deficient, P fertiliser needs to be applied each year, early in the growing season when seedlings are emerging. An experiment on a dairy farm near Boyanup from 2000 to 2003 showed no response to fertliser P over the four year life of the trial. This reinforced the recommendation that fertiliser P should only be applied when soil P approached the critical level for that soil.