PREDICTION OF PHOSPHORUS REQUIREMENTS OF DESMODIUM-INTORTUM CV GREENLEAF USING A PHOSPHORUS SORPTION INDEX AND EXTRACTABLE PHOSPHORUS

The rates of applied phosphorus required for 90% maximum yield of Desmodium intortum cv. Greenleaf were calculated from pot experiments using 24 fertilized and unfertilized soils from the Atherton Tableland, Queensland, Australia. Phosphorus required was highly correlated (r2 = 0.94) with the phosphorus sorbed (P sorbed) by the soils at a supernatant solution P concentration of 0.08 ppm. P sorbed was found to be a function of phosphorus buffer capacity at 0.08 ppm (“PBC”) and phosphorus extractable by acid (0.005 M H2SO4) or bicarbonate (0.5 M NaHCO3). PBC was highly correlated (r2 = 0.84) with a phosphorus sorption index (“PSI”) derived from one addition of 500 μg P g-1 soil. Combining PSI with acid or bicarbonate extractable P in a multiple regression equation allowed the estimation of phosphorus required with multiple correlation coefficients of. R2 = 0.80 and R2 = 0.83 respectively. Copyright © 1979 by Marcel Dekker, Inc. All Rights Reserved.