Abstract

ALCALA DE JESUS, María; HIDALGO MORENO, Claudia  and  GUTIERREZ CASTORENA, Ma. del Carmen. Mineralogy and Phosphate Retention in Andisols. Terra Latinoam [online]. 2009, vol.27, n.4, pp.275-286. ISSN 2395-8030.

Andisols are the dominant soil of the Purhepecha Plateau, Michoacan, Mexico. This type of soil is of andic characteristics, among which is a high capacity for phosphate retention, affecting normal plant nutrition. Andic characteristics are related to the nature of the amorphous clay fraction and Al-Fe humus complexes. These materials have high specific surface area and abundant active sites of phosphate retention. In the Purhepecha Plateau, mineralogic research in Andisols is not abundant and the study of amorphous minerals constituents and their relationship with phosphate retention is not frequent. A combination of analytical and mineralogic techniques (selective dissolution chemical analysis, X ray diffraction, IR spectroscopy, and electron transmission microscopy) were used to characterize the amorphous minerals and phyllosilicate clays of the Andisols clay fraction in three profiles (P.3, P.8, and P.11), and whether the amorphous minerals allophane and ferrihydrite were responsible for phosphate retention was determined since these minerals have been mentioned as the principal factors in the retention process. Amorphous minerals as allophone and ferrihydrite dominated the clay fraction of the fine earth in the three studied Andisols. The highest content of allophane was for P.3 and P.8, while ferrihydrite was P.11. In P.3 crystalline iron oxides and crystalline phyllosilicate clays of type 1:1 halloysite were present. Phosphate retention in the soils P.8 and P.11 is explained by the combined action of allophane and ferrihydrite. In P.3 retention is attributable mainly to the crystalline iron minerals, likely a hematite type. Until now, the action of these minerals on phosphate retention in Andisols of Purhepecha region had not been reported.

Keywords : volcanic ash; allophane; ferrihydrite; halloysite.

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