The ability of several soil extractants to identify copper-responsive wheat soils

Abstract

Tests with six solutions for extracting copper from soil (viz.: 1M ammonium acetate (CH3COONH4); 1M CH3COONH4 + 2% hydroquinone; 0. 5M ammonium oxalate [(NH4)2C2O4]; 0.005M diethylenetriaminepenta-acetic acid + triethanolamine + calcium chloride (DTPA + TEA + CaCl); 0.005MDTPA + 1M ammonium bicarbonate (NH4HCO3); and 0.01M ethylenediaminetetra- acetic acid (EDTA) + 1M NH4HCO3) were examined in both glasshouse and field studies for their ability to predict the responsiveness to copper fertilizer of wheat grown on a wide range of Queensland soils. The ammonium-acetate-based solutions did not extract measurable amounts of copper from soil. The usefulness of the remaining solutions was in the order EDTA-NH4HCO3>DTPA-NH4HCO3 >> DTPA-TEA-CaCl2 > (NH4)2C2O4. The EDTA-NH4HC03 method is recommended for identifying copper-responsive wheat soils in southern Queensland, and the suggested critical levels for dry matter production and grain yield are 0.4 and 0.3 ppm Cu respectively.