HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) An erratum has been published Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Rajan, S. S. S. Articles by Fox, R. L. Search for Related Content PubMed Articles by Rajan, S. S. S. Articles by Fox, R. L. Agricola Articles by Rajan, S. S. S. Articles by Fox, R. L.

Phosphate Adsorption by Soils: II. Reactions in Tropical Acid Soils¹

S. S. S. Rjan and R. L. Fox²

ABSTRACT

Phosphate adsorption by several Hawaiian and Indian soils, and the relation of phosphate adsorption to hydroxyl, sulfate, and silicate ions released in two Hawaiian soils were studied. Adsorption isotherms of some of the soils show an abrupt increase in phosphate adsorption at high concentrations.

The isotherms were analyzed applying a binary Langmuir equation (assuming two types of sites). The curve predicted by the Langmuir parameters describes the portion of the isotherm where adsorption seems to be mainly by surface ligand exchange (at low levels of phosphate adsorbed). Where additional reactions occur the experimental points deviate from the predicted curve.

Phosphate adsorption is associated with increased pH and sulfate release at low levels of phosphate adsorbed and increased silicate release throughout. The observations suggest that at low concentrations phosphate exchanges with (i) adsorbed sulfate and adsorbed silicate, and (ii) with water and hydroxyls of metal hydrous oxides and edge aluminum of clays. At high concentrations additional phosphate is adsorbed by displacing the structural silicate of clays. The increase in phosphate adsorption by structural silicate release, over that of surface exchange reactions, is about 50 and 25% in two soils containing kaolinite and allophane clays respectively.

¹ Submitted with the approval of the Director of Hawaii Agr. Exp. Sta. as Journal Series No. 1770.

² Former Graduate Student and Professor, respectively, Dept. of Agronomy and Soil Sci., Univ. of Hawaii, Honolulu, Hawaii. Present address of the senior author is: Ruakura Agr. Res. Center, P.B., Hamilton, New Zealand.

Received for publication July 24, 1974. Accepted for publication May 26, 1975.