Responses of Six Crop Species to Solution Zinc2+ Activities Buffered with HEDTA

Zinc contamination has long hampered the use of conventional nutrient solutions for attaining reproducible and severe Zn deficiencies. Chelator‐buffered solutions show promise for precisely imposing micronutrient deficiencies, but further studies are needed to fully evaluate the method and to develop methods to avoid Zn‐deficiency‐induced P toxicity. In a greenhouse study, seedlings of maize ( Zea mays L. ‘Golden Cross Bantam’), wheat ( Triticum aestivum L. ‘Yecora Rojo’), tall wheatgrass ( Elytrigia pontica [Podp.] Holub ‘Orbit’), alfalfa ( Medicago sativa L. ‘Germain's WL‐320’), soybean ( Glycine max [L.] Merr. ‘Vinton 81’), and tomato ( Lycopersicon esculentum L. ‘Jackpot’) were grown for 16 to 29 d in solutions containing 0.4 to 12 µ M total Zn. Computed Zn 2+ activities were buffered at 4 to 123 pmol L −1 by a 50‐µ M excess of HEDTA, and solution P was maintained at 10 ± 3 µ M . Zinc deficiencies ranged from mild to severe, dry matter yield minima ranged from 32 to 89% of controls, and critical Zn 2+ activities for the onset of deficiency ranged from approximately 10 to 65 pmol L −1 . The relative sensitivity of the six species to low Zn was maize > tomato > wheat > alfalfa ≈ tall wheatgrass > soybean. Shoot Zn concentrations were consistent with the widely reported critical range of 15 to 20 mg kg −1 . Zinc deficiency in the three grass species led to hyperaccumulation of P to phytotoxic levels, and leaf symptoms largely reflected this toxicity. Leaf P concentrations in the three dicots tended to be lower, but may have been within the phytotoxic range. Thus, even with P concentrations that approach soil solution values, the P toxicity that often accompanies Zn deficiency in solution‐culture experiments was not eliminated. The effects of Zn deficiency on shoot concentrations of nutrients other than P were variable, although divalent cations tended to be elevated in Zn‐deficient shoots.