Dynamics of Manganese Adsorption onto Highly Calcareous Soils of Southern Iran

ABSTRACT: Manganese (Mn) deficiency is a constraint for some crops grown on calcareous soils. Calcareous soils have a large capacity for the retention of Mn. Dynamics of Mn Adsorption onto ten calcareous soils of southern Iran were studied in a laboratory experiment. Soil samples were equilibrated with 30 mL solutions containing 800 mg Mn L-1 for five periods between 1 to 840 min and the amounts of Mn sorbed by soils were calculated and the patterns of Mn adsorption were investigated using five kinetic models. Adsorption data for Mn showed the best fit to the power function model due to relatively high values of R2 and low values of SE. Significant positive correlations were observed among the amounts of Mn adsorbed onto the most studied soils. Such correlations may demonstrate the relatively similar patterns of Mn adsorbtion in the calcareous soils studied.The a value, initial Mn sorption rate constant, showed significant positive correlations with the contents of clay and OM and the value of CEC but negative correlation with pH. Therefore, it appears that the rate of Mn adsorption increased as the contents of clay and OM or the value of CEC increased. Significant negative correlations were observed between the amounts of Mn adsorbed at different shaking times with soil pH and CCE. It appears that higher pH or calcium carbonates caused the lower adsorption of Mn. Significant positive correlations were observed between the amounts of Mn adsorbed at different shaking times and some soil properties including the contents of clay and OM and the value of CEC. It appears that clay and organic matter are the main sites for Mn adsorption throughout the dynamics study.