Extractability of major and trace elements from agricultural soils using chemical extraction methods: Application for phytoavailability assessment

Abstract

Abstract To assess soil-to-plant transfer of various elements more precisely, the concentrations of the elements extracted from soil samples using eight chemical solutions were compared with the results of a pot cultivation experiment of komatsuna (Brassica rapa L. var. perviridis) or buckwheat (Fagopyrum esculentum M.) using the soils. From agricultural fields in Aomori, Japan, 16 soil samples were collected. Elements in the samples were extracted using acids (1 mol L−1 HNO3, 0.1 mol L−1 HNO3, 0.01 mol L−1 HNO3), chelating agents (0.05 mol L−1 EDTA), neutral salt solutions (1 mol L−1 NH4OAc, 1 mol L−1 NH4NO3, 0.01 mol L−1 CaCl2) and pure water. The 28 elements in the extracted solutions and plant samples were determined. The extractability of many metals was higher in 1 mol L−1 HNO3, 0.1 mol L−1 HNO3 and the 0.05 mol L−1 EDTA solutions than in the other extractants. Higher extractability using the NH4OAc solution than the NH4NO3 solution was observed for some elements, in particular U. Extractability by pure water was not always lowest among these methods, probably because of dispersion of colloidal substances in the extracted solution. The pot cultivation experiment showed that the concentrations in soil and in the extracted fraction using 1 mol L−1 HNO3, 0.1 mol L−1 HNO3 or the EDTA solution did not correlate with the concentration in plant samples for most elements. Plant uptake of Zn, Y and La by komatsuna correlated well with their concentrations in extracts with neutral salt solutions or 0.01 mol L−1 HNO3. Concentrations of Al, Cu and Cd in buckwheat were also correlated with the concentrations in the extracts.