Phosphorus adsorption in soils under forest and savanna from Northern Amazon, Brazil

Abstract

Studies on maximum phosphorus adsorption capacity (MPAC) in soils from Roraima State and attributes that interfere with the magnitude of this characteristic are relevant and motivated this study. In this context, topsoil samples (0-0.20 m) from four soil classes (Oxisol-LA and Oxisol-LV [ITÃ, Caracaraí]; Oxisol-LA [Serra da Prata, Mucajaí]; Oxisol-LA and Ultisol-PA [CCA, Boa Vista]; Oxisol-FT [Bonfim] and Alfisol-SN [Surumu, Pacaraima]) representative of Roraima State were used in this study in order to determine the influence of soil physical, chemical, and mineralogical attributes on MPAC. Air-dried soil samples of 2.5 g and 0.01 mol L-1 CaCl2 (25 mL) solution were stirred for 24 h, being added P in the form of KH2PO4 at concentrations of 0-60, 0-80, and 0-110 mg L-1. P was analyzed in the supernatant for determining its adsorbed amount (P-rem). Adsorption values were fitted to the Langmuir isotherm in order to assess MPAC. Correlation tests were performed between MPAC and binding energy, pH, organic matter, clay, and CEC. MPAC values ranged from 14.50 to 527.93 mg kg-1 in the soil. The soils FT-Bonfim and LV-ITÃ presented a higher MPAC. Considering the representative soil classes in the State, MPAC does not correlate with any of the assessed attributes. In the soil classes Oxisol and Ultisol, MPAC has a negative and significant correlation with binding energy.