PHOSPHORUS FERTILISER REQUIRMENTS FOR PLANT AND RATOON CROPS ON SOILS WITH VERY HIGH PHOSPHORUS SORPTION CHARACTERISTICS

THE ORIGINAL PHOSPHORUS (P) guidelines for sugarcane were based solely on BSES-P critical values but with recognition of different requirements for plant and ratoon crops. These guidelines were modified in the SIX EASY STEPS program to reflect the ability of soils to �sorb� P by considering the phosphate buffer index (PBI) value of a soil in combination with the BSES-P value. However, P fertiliser was not recommended for soils with BSES-P > 50 mg/kg, irrespective of PBI values. There was concern that soils with very high PBI values (>280) may still require some P fertiliser even if the BSES-P value was > 50 mg/kg. To evaluate the P requirement of sugarcane grown in these soils, a trial was established on a Hewitt series soil at the Tully Sugar Experiment Station with a BSES-P of 109 mg/kg and PBI of 1001. The application of P at planting did not improve germination but it did increase tillering and stalk height in the plant crop which translated to higher cane and sugar yields at harvest. It also resulted in significantly higher industry profitability. There was no response to applied P in the ratoon crop. P fertiliser is now recommended for plant cane crops where soil test results report very high PBI values (>420) and BSES-P values in the range of 50�120 mg/kg. The application of P fertiliser to ratoon crops grown in these soils is optional. P is not recommended where BSES-P values are >120 mg/kg irrespective of the PBI value.