EDTA‐Ammonium Carbonate Soil Test for Zinc

Abstract

A soil test was developed for the diagnosis of Zn‐deficient soils. The test consists of shaking 10 g soil with 20 ml of extractant (pH 8.6) containing 0.01M EDTA (ethylenediaminetetraacetic acid) and 1M (NH₄)₂CO₃. After 30‐min shaking period the suspension is filtered, and Zn is determined directly in the filtrate by means of atomic absorption spectrophotometry. The new soil test was evaluated on 42 Colorado neutral and high lime soils whose response to Zn was determined in the greenhouse with corn (Zea mays) as the test crop. A critical level of 1.4 ppm of extractable Zn separated the Zn‐deficient from the nondeficient soils. The new Zn soil test compares favorably with the dithizone method and is an improvement over the 0.1N HCl method. Unlike strong‐acid extractants, the new procedure suppresses the dissolution of carbonates and oxides, and thereby avoids extraction of occluded Zn.