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 m M 2‐(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 μ M total chelated Zn), to fully Zn sufficient where (Zn 2+ ) = 10 −8.8 M (4.00 μ M total chelated Zn). Using 200.0 μ M 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.