Abstract
A part of ferric, alminium and tri-calcium phosphate becomes soluble or available in the presence of humic acid. Mutual reactions of humic acid, insoluble or soluble phosphates and hydroxides in the buffer solution of acetic acid and Na-acetate were studied, and the mechanism of phosphate release by humic acid was partially revealed. The results are summarized as follows; (1) The hydrolysis of Fe-, Al- and Ca-phosphate were accelerated and the dissolution as total salt were depressed by humic acid. (2) Humic acid released phosphate by preventing the fixation of soluble phosphate by Fe-, Al- or Ca-hydroxides and partially dissolving the phosphates thus formed. (3) A characteristic humate was formed from each humic acid combining with Fe, Al, or Ca-hydroxide in the pH range in which it dissolved or dispersed.
