Extraction and Analysis of Soil Solution of Phosphate Rock and Acid Treated Soil

Increasing basic phosphate rock (PR) rates and acid loads were applied to an acidic sandy soil in a laboratory experiment. 'Total' amounts of potentially toxic elements in the soil and PR samples were determined by inductively coupled plasma (ICP) spectrometry after acidic, microwave digestion. Soil solution was extracted from wet soil by centrifugation with a speed corresponding to the suction power exerted by plants at the conventional wilting point. Addition of PR generally decreased rather than increased metal concentrations in the soil solution because of its pH elevating, immobilizing effect. Except for Pb, the extreme acid treatment compensated for the immobilizing effect of PR. Release of Cd (expressed as soil solution concentration in percentage of the total amount in soil + PR) was generally highest among elements at every treatment, and Cr was the least mobile metal. The one-time, high rate of PR application did not make a direct environmental risk probable.