Soil aluminum and iron fractions and their relationships with P immobilization and other soil properties in andisols of costa rica and panama

Abstract

The immobilization of P is a significant fertility limitation of Andisols in Central America. It is believed that soil Al and Fe fractions have an important influence on P availability. This study was conducted to obtain information on the various forms of Al and Fe in ten pedons derived from volcanic ash in Panama and Costa Rica. Correlations between these Al and Fe fractions and P immobilization were measured by different methods.

The Al and Fe fractions, extracted by acid ammonium oxalate, 4M KOH, sodium pyrophosphate and dithionite‐citrate, were determined, and the correlations between these fractions, P immobilization, and other soil properties made.

It was observed that oxalate extractable Al correlated significantly with P immobilization, which had values of over 85% by the New Zealand method and 96% by the isotherm method. The Al concentration corresponding to this immobilization was over 2%. The difference between oxalate extractable Al and pyrophosphate extractable Al (inorganic Al fraction) correlated with P immobilization also. The pyrophosphate extractable Al fraction had the lowest concentrations and did not correlate with P immobilization. The NaF‐pH and dithionite‐citrate extractable Al correlated significantly with P immobilization.

Oxalate extractable Fe correlated with the P retained by the isotherm method, but dithionite‐citrate extractable Fe was negatively correlation with P immobilized. No correlations were found between the pyrophosphate extractable Fe and other soil properties.