Fig. 4. Phosphorus retention by the pure minerals expressed as the percentage of added P that was absorbed during a single point isotherm (adsorption). Desorption expressed as P retained on samples after four sequential desorptions with 0.01 M CaCl₂ ([P remaining on sample after four desorptions/P remaining on sample after previous single point adsorption] x 100). Error bars indicate standard deviation. Least significant difference at P < 0.05 was 6.5 and 10.7 for adsorption and desorption, respectively.