Methods for estimating phytoavailable metals in soils

Abstract

Total concentration is not a reliable indicator of metal phytoavailability in soils. There is a dearth of single universal multielement methods with critical value. Therefore, this study was implemented to select appropriate methods for evaluation of phytoavailable metal status in peaches grown in alkaline alluvial soils. Component plant parts (leaf and fruit flesh and peel) and soil samples were collected from 21 orchards. Fourteen extraction methods were applied to the soils to determine the phytoavailable metal content of the soils. Metal [iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), chromium (Cr), nickel (Ni), cobalt (Co), lead (Pb), and cadmium (Cd)] concentrations in leaf, flesh, and peel samples were assayed, and the relationship was investigated among metals in component parts of the plant. Metals were assayed by various methods to select the most representative method. The methods of aqua regia, Morgan extraction solution, ammonium acetate (NH4OAc; pH4.8), 0.01M disodium ethylenediamine-di-o-hydroxyphenylacetic acid (Na2EDDHA), and sodium acetate (NaOAc) + diethylenetriaminepentaacetic acid (DTPA) for Fe and DTPA + triethanolamine (TEA) + calcium chloride (CaCl2), 0.05 N hydrochloric acid (HCl) + 0.025 N sulfuric acid (H2SO4), NH4OAc (pH4.8), 0.05M ethylenediaminetetraacetic acid (EDTA; pH7.0), 0.01M Na2EDDHA, and 1M ammonium bicarbonate (NH4HCO3) + 0.005M DTPA for Ni were well correlated to Fe and Ni in the leaves, respectively. The main factors affecting Fe and Ni availability in the soils were compared with the other methods. Therefore, based on this study, 0.01M Na2EDDHA should be used for determination of phytoavailable Fe and Ni status in peaches grown on alkaline alluvial soils. Poor correlation was found among the rest of the metals assayed by the methods, concentrations of these metals in component parts of the peach trees, and the examined soil properties. Metal content of the flesh had low correlation coefficients with the examined properties.