R.C. BRUCE

Abstract

Three areas of known fertiliser history (nil, intermediate and high amounts of phosphorus) were sampled on each of the two main soil types of the Coolum Research Station, south east Queensland (Coolum sand and Peregian sandy loam). Soil from 0–5 cm was potted and cropped with Setaria anceps cv. Narok in the glasshouse for eight harvests.
There was sufficient available residual phosphorus in soils which had previously received high amounts of phosphorus to give maximum dry matter yields of setaria throughout the experiment in the case of the Peregian loamy sand and for six harvests in the case of the Coolum sand. Soils of intermediate fertiliser history could not produce maximum dry matter yields without additional phosphorus, but they still produced yields far in excess of those for their respective virgin soils.
Pasture development and fertiliser application increased soil organic carbon, total nitrogen, organic phosphorus, total phosphorus, acid extractable phosphorus and exchangeable cations. The bulk of the residual phosphorus was in the inorganic form.
As indices of soil phosphorus availability, acid extractable phosphorus, "a" values (from first harvest or from sum of eight harvests), and the fresh fertiliser equivalent (interpolated from the uptake graph for sum of eight harvests) all showed promise. There were not enough soils to fully test them.