A major nutritional problem to crops grown in highly weathered Brazilian soils is phosphorus (P) deficiencies linked to their low availability and the capacity of the soils to fix P in insoluble forms. Our studies examined factors that might influence P behavior in soils of the Amazon region. This study was conducted to evaluate the maximum phosphate adsorption capacity (MPAC) of the soils developed from mafic rocks (diabase), their parent materials and other factors resulting in the formation of eutrophic soils having A chernozemic horizon associated with Red Nitosols (Alfisol) and Red Latosols (Oxisol) of the Amazonian environment. The MPAC was determined in triplicates as a function of the remnant P values. The different concentrations used to determine the MPAC allowed maximum adsorption values to be reached for all soils. The Latosol (Oxisol) and Nitosol (Alfisol) soils presented higher phosphate adsorption values that were attributed to the oxidic mineralogy and high clay texture while the Chernosol (Mollisol) soils presented the lowest phosphate adsorption values.