Kinetics of phosphorus reactions in calcareous soils

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Abstract
Phosphorus sorption kinetics was studied using four calcareous soils which were reacted with MCP solutions. Changes in P solution concentration were determined and total sorption was calculated for reaction periods ranging between 1 h to 21 days and solution concentrations ranging from 0 to 200 mg P/1. Calculations of three separate components (forms) of sorbed P, Pwe– water extractable P; Pbic‐ bicarbonate extractable P and Pns‐ non soluble P were obtained from a sequence of extractions. Total sorption consisting of fast sorption terms and of time dependent reactions which contributed to the overall process increased with increasing initial solution concentrations. Of the different components, Pwedecreased moderately with time or with solution concentration and was associated with equilibrium sorption. Pbicincreased with time as the reaction started, reached a maximum and then started to decrease. Pnsslightly increased at the initial reaction stages, and at the time Pbicstarted to decrease, its formation rate increased. Thus, it was hypothesized that the bicarbonate extractable sorbed P represents precipitation of slightly soluble Ca‐P compounds whereas Pnsrepresents that for the precipitation of sparingly soluble or nonsoluble Ca‐P compounds

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