Boron adsorption in Oxisols from Minas Gerais, Brazil.
Edson Marcio Mattiello1, Nicholas B. Comerford1, Hugo A. Ruiz2, Ivo R. Silva2, Nairan F. Barros2, and Julio C. L. Neves2. (1) PO Box 110290, University of Florida, University of Florida, Soil & Water Science Department, Gainesville, FL 32611-0290, (2) Solos, Universidade Federal de Vicosa, Departamento de Solos, Campus-UFV, Vicosa, 36570-000, Brazil
Boron (B) deficiency is the most widespread micronutrient problem in eucalypt plantations in Brazil, mainly in the cerrado ecosystem. Boron fertilization is used to overcome deficiencies in these areas. With the addition of B, the element can be distributed between the solid and solution soil phases depending upon B’s affinity for the different soil constituents. The goal this work was to evaluate the role of organic matter and pH in the B adsorption using five commonly Oxisols occurring in Minas Gerais, Brazil. To determinate the quantity of adsorbed B, 4 g of oven dry soil were shaken for 24 h, in polyethylene tubes, with 20 mL of CaCl2 (5 mmol/L) solution containing 2 and 8 mg/L of B in soil samples without and with two methods of organic carbon removal (H2O2 and NaOCl oxidation) and with and without calcium carbonate application. The suspension was centrifuged for 15 min at 2000 rpm, filtered, and B was accomplished colorimetrically. Soil B adsorption was obtained by subtracting B in soil solution from B added. Between 38 and 80% of organic carbon was removed from the soil. B adsorption was higher in clayey Oxisols than in coarser soils. The percentage of adsorbed B varied from 1 to 40%, increasing with clay content. Calcium carbonate promoted an increase in the amount of adsorbed B, with the most pronounced effect occurring at higher added B levels. Organic carbon removal using NaOCl promoted higher B adsorption than H2O2. Boron adsorption remained constant or increased with the removal of organic carbon. Adsorbed B was mainly explained by B concentration, pH and clay content. In conclusion, the mineral phase (clay) and soil pH are more important in explaining B adsorption in these soils than is the organic phase. Clay content and soil pH are important characteristics that should be considered in boron fertilization.