Premium
Relationships between Sesquioxides, Kaolinite, and Phosphate Sorption in a Catena of Oxisols in Malawi
Author(s) -
Karim May I.,
Adams W. A.
Publication year - 1984
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1984.03615995004800020037x
Subject(s) - sorption , goethite , kaolinite , gibbsite , phosphate , hematite , oxisol , chemistry , environmental chemistry , soil water , geology , inorganic chemistry , mineralogy , soil science , adsorption , organic chemistry
A catenary sequence of Oxisols was examined to determine the phosphate sorption capacity of the oxic horizon and to identify the minerals responsible for this property. The phosphate sorption capacity of the six soil samples taken along the sequence was found to increase downslope as far as the midslope, then to decrease towards the valley bottom. All samples contained quartz, kaolinite, goethite, and hematite; gibbsite was identified in one sample. Aluminium‐substituted goethite was found to be the mineral mainly responsible for phosphate sorption capacity and the one that caused variations in this property along the slope sequence. Significant correlations between phosphate sorption capacity and both Fe and Al extracted by citrate‐dithionite are explained by their occurrence in this oxide. Amounts of noncrystalline oxides were low and there was no correlation between phosphate sorption capacity and amounts of either Fe or Al extracted by oxalate. Kaolinite was calculated to account for 12 to 29% of the phosphate sorption capacities of the soils but there was no significant correlation between the two. Hematite, which showed a progressive decrease in content downslope, had no measurable influence on phosphate sorption capacity. The distribution of Fe oxides along the sequence suggests rather slow pedogenetic change in the horizons sampled with goethite, the main oxide product of contemporary soil‐forming processes.