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Calcium Phosphate Fertilizers: II. A Petrographic Study of Their Alteration in Soils¹

ABSTRACT

As a supplemental study to pot-culture tests in which six calcium phosphates were investigated, petrographic examinations were made of the fertilizer residues and surrounding soils. The materials tested were Ca(H₂PO₄)₂ · H₂O, CaHPO₄ · 2H₂O, CaHPO₄, Ca₄H(PO₄)₃ · 3H₂O, Ca₃(PO₄)₂, and Ca₁₀(PO₄)₆(OH)₂).

The purpose was to determine the physical and chemical alterations that the materials had undergone while in a soil environment and in the presence of feeding roots. Correlations between these observations and plant response were sought.

Some correlation was found between plant response and; (a) relative rates of solution or solubilities of the phosphates, and (b) chemical alterations of the phosphates. Positive evidence was found for 4 hydrolysis reactions, 2 of which confirm the postulated formation of octocalcium phosphate and apatite. Other observations lend new support to the concept of contact feeding by plant roots.

¹ Contribution of the Research Branch, Division of Chemical Development, T.V.A., Wilson Dam, Alabama. Presented before Div. II, Soil Science Society of America, Nov. 21, 1957 at Atlanta, Georgia.

² Research Chemists.

Received for publication May 24, 1957. Accepted for publication July 11, 1957.