Phosphorus behavior in tropical soils. I. Adsorption isotherms

Abstract

Tropical soils containing large amounts of iron and aluminum sesquioxides can fix high amounts of phosphorus. The process is usually studied by way of adsorption isotherms. This paper shows that at intermediate concentration equilibrium solutions, the phosphorus adsorption can be represented either by the Langmuir or Freundlich equations. High correlations were obtained between the maximum adsorption and the concentration of the free iron oxides extracted by citrate-ditionite. However there were no significant correlations with the aluminium sesquioxide extracted with 0.5N sodium hydroxide. The initial phosphorus fractions added to the soils were bound with high energy to the iron constituents up to the maximum adsorption value, after which binding energy tended to decrease. In contrast, the combination of phosphorus with the aluminium constituents increased constantly as the concentration of added phosphorus was increased.