HEDTA-Nitrilotriacetic Acid Chelator-Buffered Nutrient Solution for Zinc Deficiency Evaluation in Rice

Chelator-buffering methods with N-(2-hydroxyethyl)ethylenedinitrilotriacetic acid (HEDTA) are used to elucidate Poaceae growth response to micronutrient metal activities including (Zn 2+ ), but reliable hydroponic methods that maintain stable (Zn 2+ ) for evaluating Zn deficiency in rice (Oryza sativa L.) have not been reported. The objective was to develop a chelator-buffered method that gauges rice growth response to (Zn 2+ ) in an otherwise chemically stable environment. Using GEOCHEM-PC to estimate solution activities, an aerobic HEDTA-nitrilotriacetic acid (NTA) dual-chelator method was developed that imposed five (Zn 2+ ) levels on cv. IR-36 seedlings for 21 d after transplanting (DAT) in a growth chamber. Control of pH 5.50 ± 0.05 using 3.0 mM2-(4-morpholino)-ethanesulfonic acid (MES) combined with periodic adjustment was critical to preserving target (Zn 2+ ). Solution treatments ranged from Zn deficient, where (Zn 2+ ) = 10 -10.0 M (0.25 μM total chelated Zn), to fully Zn sufficient where (Zn 2+ ) = 10 -8.8 M (4.00 μM total chelated Zn). Using 200.0 μM total chelated Fe(III), adequate Fe was maintained at (Fe 3+ ) = 10 -14.3 M. Phosphorous supply was controlled to prevent toxic P accumulation at low (Zn 2+ ). With increasing (Zn 2+ ), total biomass at 21 d ranged from 0.94 to 1.90 g plant -1 . Shoot Zn responded to (Zn 2+ ), not total chelated Zn 2+ , and roots responded similarly. Critical (Zn 2+ ) for normal growth was 10 -9.1 M, and leaf Zn-deficiency symptoms were observed at (Zn 2+ ) ≤10 -9.4 M (≤28 mg Zn kg -1 shoot). The HEDTA-NTA method provides a rapid and reliable means for evaluating Zn deficiency tolerance in IR-36 via diagnostic visual and physical symptoms in response to a range of (Zn 2+ ) levels.