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Abstract A 0.5N HC1 plus 0.05N A1C13 reagent using a 1:5 soil: extractant ratio by volume and an extraction period of 5 minutes has been proposed for Cu. For meaningful analyses, concentrations of 0.01 ug Cu/ml were required for direct aspiration. With instrumentation short of this requirement a single complexing‐organic reagent consisting of 2 g APDC(ammonium‐1‐pyrrolidine dithiocarbamate) dissolved in 600 ml 95% ethanol and then mixed with 400 ml n‐butyl acetate has been developed. This reagent renders the method expeditious, increases storage stability for APDC up to 6 months, and provides improved separation of organic phase and extractant. The method has been tested on soils from numerous field experiments and correlated with crop response using wheat, soybeans, and sorghum on organic soils (Histosols) and wheat on mineral soils (Ultisols). The probability of crop responses to Cu and extractable Cu has been formulated and applied in practice.
Mehlich et al. (Wed,) studied this question.