Biofortifying sunflower with Zinc (Zn) aminochelates: a promising strategy for calcareous soil conditions

BACKGROUND: Zinc (Zn) deficiency in calcareous soils limits crop productivity and restricts nutritional quality in edible plant products. AIMS: This study assessed the effectiveness of Zn-aminochelates, compared with conventional ZnSO₄, applied through various application methods, in improving physiological traits, growth, yield, and seed Zn biofortification in sunflower (Helianthus annuus L.) under calcareous soil conditions. METHODS: A field experiment was conducted using a randomized complete block design with three replications. Zn(glycine)₂ [Zn(Gly)₂], Zn(methionine)₂ [Zn(Met)₂], and ZnSO₄ were applied through seed priming (2% solution), fertigation (4 L ha⁻¹ for Zn-aminochelates and 40 kg ha⁻¹ for ZnSO₄), and foliar spray (0.2% w/v, 2 L ha⁻¹ per application) at key growth stages. Control plots received untreated seeds or water. RESULTS: Compared with ZnSO₄, Zn-aminochelates significantly improved seed yield, biomass production, and Zn accumulation. Foliar application of [Zn(Met)₂] was the most effective treatment, increasing seed yield by approximately 85%, oil yield by about 2.5-fold, and seed Zn uptake by nearly twofold, while also enhancing physiological traits, antioxidant enzyme activities, and protein accumulation. The N/S ratio decreased concomitantly with increased seed oil content. CONCLUSIONS: The superior performance of methionine-based Zn chelates is likely linked to their role in sulfur metabolism, enhanced Zn mobility, and improved antioxidant regulation. Overall, foliar application of Zn-aminochelates represents an effective and practical agronomic biofortification strategy for improving productivity and nutritional quality of sunflower grown on calcareous soils.