螯合铁是指与有机分子（螯合剂）化学结合的铁（Fe），以使其在营养液中保持溶解状态并可供植物吸收。未螯合的铁在正常的生长pH水平下会迅速氧化并从溶液中析出，从而使植物根系无法吸收。最常见的螯合剂是EDTA（在pH 6.0以下稳定）、DTPA（在pH 6.5以下稳定）和EDDHA（在pH 9.0以下稳定）。
关键事实
- Unchelated iron precipitates above pH 6.5 and becomes unavailable to plants
- EDTA chelate: effective at pH 4.0–6.0 — suitable for most hydroponic systems
- DTPA chelate: effective up to pH 6.5 — better for slightly higher pH ranges
- EDDHA chelate: stable up to pH 9.0 — used in soil and high-alkalinity water
- Iron deficiency causes interveinal chlorosis on new leaves (yellowing between green veins)
- Most complete hydroponic nutrients contain EDTA or DTPA chelated iron