Response of annual medic pasture to superphosphate applications and the correlation with available soil phosphorus

Abstract

The response of annual medic dominant pastures to residual and currently applied phosphorus was examined in twelve experiments in cereal areas of South Australia. The experimental sites had been sown in the previous year to wheat with nine rates of phosphorus ranging from 0-48 kg P/ha applied as superphosphate. The 0.5M NaHCO3 extraction provided an effective index of residual available soil phosphorus after the crop and the amount of phosphorus detected by this soil test varied from 24-43 per cent of the total phosphorus applied as superphosphate on sandy and heavier textured soils respectively. Regression analysis showed that an available soil phosphorus level of 32-38 kg P/ha 10 cm was sufficient to produce 90 per cent of maximum pasture yield on the sandy soils but 41-47 kg P/ha 10 cm was required on heavier textured soils. Percentage phosphorus in the dry matter in spring was not correlated with pasture response.