Maximum Phosphorus Adsorption Capacity Adjusted to Isotherm Models in Representative Soils of Eastern Amazon

Abstract

Most soils of the Amazon present low natural fertility and may also present high phosphorus (P)–fixation capacity. Clay fraction mineralogy, organic carbon, cation exchange capacity (CEC), and pH are among the factors that influence P adsorption. In this study, we aimed to evaluate the maximum P-adsorption capacity (MPAC) and correlate parameters of the isotherm models and the MPAC with soil attributes. Soil samples were collected in 12 forest soils in the state of Pará. We built Langmuir and Freundlich isotherms, and their parameters correlated with soil attributes. MPAC was greater in Plinthosols, among the soils studied at both depths. In superficial soil layers, the parameters of Langmuir-Freundlich equations correlated with clay content, pH, organic matter (OM), aluminum oxide (Al2O3), and iron oxide (Fe2O3) at both depths. The Langmuir model is more representative of the adsorption of P relative to the Freundlich model for the Amazon region soils, where it is necessary to make use of organic matter and pH control as a means of reducing the retention and P and maximize the effects of fertilization phosphate.