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The objective of this study was to examine the effect of aluminum ion on the movement of phosphate ion. Rectangular paraffin was blocks having cylindrial cavities of 45 min in i.d. and 100 ㎜ deep were packed to a bulk density of 1.3 Mg m^(-3) with the moist mixtures in four different ways: (1) the mixture of sand and Al^(+3)-saturated resin, (2) the mixture of sand and solid Al₂O₃ (2% w/w), (3) the mixture of sand, Al^(-3)-saturated resin and solid Al₂O₃, and (4) sand alone as a control treatment. To simulate a one-dimensional vertical diffusive phosphate transport from an instantaneous planar source into a semi-infinite system, 0.2g of finely ground ^(32)P-KH₂PO₄ powder was applied as uniformly as possible on the surface of each mixture. At different desired periods of incubation, each column was sectioned in 2 ㎜ intervals. Samples were taken simultaneously from each section for moisture contents and chemical analyses. The pH (1 : ) profile of the system was measured and P, K and Al profiles for both water- and acid-extractable fractions were then mapped out, respectively. The results were as follows: (1) Phosphate transport was retarded in the presence of exchangeable aluminum ion. (2) Retardation of phosphate movement by exchangeable aluminum ion was characterized by lowering of pH. (3) Phosphate transport was not retarded in the presence of solid Al₂O₃ alone. (4) Retardation of phosphate movement was further enhanced in the presence of exchangeable alumimum ion with solid Al₂O₃. (5) It was concluded that the interaction between aluminum and phosphate was a precipitation rather than a surface adsorption.
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