On heavy metals in soil; Rationalization of extractions by dilute salt solutions, comparison of the extracted concentrations with uptake by ryegrass and lettuce, and the possible influence of pyrophosphate on plant uptake

Extractions of Cu, Zn, Cd and Pb from soils by dilute salt solutions have been rationalized by a simple chemical equilibrium relation which includes the total load of metals, soil pH, soil cation exchange capacity (CEC), and extractant ionic strength. Correlations between metal uptakes by ryegrass and lettuce with calculated concentrations of Cu, Zn, or Cd in a fictitious soil solution at zero ionic strength are comparable to those obtained with the weakest salt solutions, 0.1 mol . l(-1) NaNO3 and 0.05 mol . l(-1) CaCl2. The other salt solutions correlate slightly less well. Uptake of Pb is not represented well.