Laboratory tests were calibrated for detection of soils supplying inadequate Zn for normal growth of corn plants ( Zea mays L.). The available Zn tests under investigation were based on amounts of Zn extracted by 0.1 N HCl, dilute HCl‐H 2 SO 4 , ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). The EDTA procedure gave the best separation of soils supplying either adequate or inadequate Zn for corn plants grown in the field. The “critical” level of EDTA‐extractable Zn for the 10 soils under study was approximately 0.8 ppm. Soils also were separated into Zn deficient and Zn sufficient categories by a three variable equation, Ŷ = 780.2 + 68.8X 1 − 101.3 X 2 − 0.4 X 3 ; where Ŷ = Zn availability index, X 1 = ppm dilute HCl‐H 2 SO 4 extractable Zn, X 2 = soil pH, and X 3 = ppm dilute HCl‐H 2 SO 4 extractable P. A Zn availability index of 135 gave the separation.
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Alley et al. (1972) studied this question.