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Availability of Natural Phosphates According to Energy Changes¹

ABSTRACT

A study of the availability of natural phosphates to oats showed that the amount of phosphorus harvested by the plants was related to the relative driving energies of the different colloidal systems mixed with the rock phosphate.

H-amberlite, mixed with rock phosphate, was the most effective system for increasing the availability of the phosphorus. The other colloidal systems were decreasingly effective in the following order: H-bentonite, H-Putnam, and H-humus.

The study of the energy changes associated with pH, total hydrogen, active calcium, and total calcium, calculated into bonding energy and into energies of exchange revealed that the weathering of the phosphorus in the apatite was related to the active calcium ions as well as to the active hydrogen of the colloidal system. The colloidal systems arranged in order as effective weathering agents were as follows: Amberlite IR-120, Wyoming bentonite clay, Putnam clay, kaolinite clay, and humus.

¹ Contribution from the Department of Soils, Missouri Agr. Exp. Sta., Journal Series No. 1393.

² Professor of soils, University of Missouri.

Received for publication September 9, 1954.