Effect of soil properties on copper release in soil solutions at low moisture content.

Copper partitioning at moisture content of 1.2-fold the field moisture capacity (corresponding to a soil water potential of 7.84 J/kg; pF = 1.9) was studied in 11 soils with pH 3.4 to 6.8 and an organic matter content of 4.1 to 233 g C/kg. Soil solutions were separated with the centrifuge method and analyzed to determine pH, Cu2+ activity, dissolved organic carbon, and Cu, Ca, Mg, and Na concentrations. Soil organic matter content, total Cu content, and soil pH were the main variables explaining variation in Cu activity in soil solutions. Based on total Cu, soil organic matter content, and soil solution pH, the Windermere Humic Aqueous Model (WHAM) VI assemblage model provided estimates of Cu2+ activity, {Cu2}, with a root mean square error of the predicted pCu (i.e., -log{Cu2+}) of 0.77.