Chemical speciation and suitablity of soil extractants for assessing Cu availability to maize (Zea mays L.) in acidic soils

Twenty surface (0-15 cm) samples of acidic soils were analysed for different chemical fractions of soil Cu namely; water soluble (WS), exchangeable (EX), lead displaceable (Pb-disp.), acid soluble (AS), Mn oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline Fe oxide occluded (CFeOX), residual (RES) and also for soil extractable Cu using DTPA (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich 3 (pH 2.0), Modified Olsen, 0.005 MCaCl2, 1 M MgCl2 extractants and ion exchange resins to understand the significance of different chemical fractions of Cu and suitability of soil extractant for predicting Cu availability to maize plants. Chemical fractions of Cu in acidic soils could be arranged in the following order: RES > MnOX > AFeOX > OB > CFeOX > AS > EX > Pb-disp. > WS. Chemical fractions of Cu in acidic soils and Cu extracted by the examined soil extractants were correlated with general soil properties. Water soluble (WS) and organically bound (OB) fractions of soil Cu showed significant and positive correlation with Cu uptake by maize. Among different examined soil extractants, DTPA (pH=5.3) and Mehlich 3 (pH = 2.0) showed significant and positive correlation with the dry matter yield, Cu concentration and uptake by maize plants in acidic soils.