Modification of Standardized European Soil Sequential Extraction Method for Evaluation of Plant-Available Amounts of Selected Elements

Abstract

The extractability of As, Cd, Cu, Pb, and Zn with 0.01 mol l^-1 CaCl₂ solution characterizing the plant-available amount of elements and that with 0.11 mol l^-1 CH₃COOH solution representing the first step of sequential extraction procedure SM&T EUR 14763 EN characterizing the exchangeable fraction, and the relationships between element contents in experimental plant (radish and spinach) and soil extracts were investigated. A pot experiment with soil amended by addition of sewage sludge or treated with soluble compounds of toxic elements was carried out in two vegetation periods. Because of ambiguous response of plants to addition of individual elements to the soil, the results of regression analysis were ambiguous as well even if the extraction agents showed differences in element mobility. 0.01 mol l^-1 CaCl₂ seemed to be more convenient for As, Cu, and Pb, especially for the above-ground part of radish. For cadmium and zinc, exchangeable portion of these elements closely correlated with the element contents in both radish and spinach. The 0.01 mol l^-1 CaCl₂-extractable contents were most likely affected either by element uptake by plants during vegetation or by soil sample processing after harvest including sample preparation for analysis. Thus, 0.01 mol l^-1 CaCl₂ seems to be a suitable extractant for evaluation of plant-available amounts of potentially toxic elements in soil and can be reasonably included in the sequential extraction scheme as the first extraction step.