RESPONSE OF CAULIFLOWER TO PHOSPHATE FERTILIZER PLACEMENT AND SOIL TEST PHOSPHORUS CALIBRATION ON A KARRAKATTA SAND

The effect of placement (broadcast versus banded) and level of phospho rus (P) applied as superphosphate at 0 to 450 kg P/ha was measured usi ng the yields of cauliflower (Brassica oleracea var botrytis) on newly cleared Karrakatta sands of low natural P fertility. While there was a significant (P<0.01) yield response to level of P, there was no sign ificant response to fertilizer placement. Phosphorus recovery efficien cy by curds (P uptake curds/P applied both in kg/ha) decreased from 0. 35 at 20 to 0.09 at 320 kg applied P/ha. Phosphorus recovery efficienc y by whole plants decreased from 0.58 at 20 kg P/ha to 0.18 at the hig hest level. Bicarbonate-soluble P extracted from the top 15 cm of soil was determined on residual P sites from experiments over two years wh ere P was applied from 0 to 450 kg P/ha. These soil test values were r elated to yield. The critical soil test values required for 95 and 99% of maximum yield were 40 and 55 mu g/g, respectively. The level of fr eshly-applied P required for either 95 or 99% of maximum yield varied from 108 to 175 kg P/ha, respectively at <5 mu g/g soil test P to 0 at the critical values. Phosphorus in the youngest expanded leaf at butt oning required for 95 and 99% of maximum yield was 0.46+/-0.02 and 0.4 7+/-0.02%, respectively.