Effects of Seed Coating Treatments and Plant Density on Sunflower (Helianthus annuus L.) Seed Yield and Quality

Abstract

Optimizing plant density and seed enhancement technologies is critical for improving crop productivity under varying agroecological conditions. This study aimed to investigate the individual and combined effects of seed coating and plant density treatments on emergence, yield, and quality traits of oilseed sunflower (Helianthus annuus L.) over two growing seasons (2018–2019) in Tokat-Kazova, Türkiye. A split-plot design was employed with three plant spacings (70 × 30, 60 × 30, and 45 × 30 cm) as main plots, and 14 seed coating treatments, combinations of fungicides, insecticides, micronutrients, and plant growth regulators, as subplots. Results revealed that denser plantings significantly improved seed yield per unit area, with the highest yield (6033.4 kg ha⁻¹) recorded in the 45 × 30 cm spacing combined with hormone-based seed coatings. The greatest emergence rate (97.8%) was obtained in hormone-coated seeds, whereas the largest head diameter (18.3 cm) was observed in uncoated dehulled seeds in the first year. Seed coatings containing fungicide + insecticide consistently enhanced both emergence and yield across both years. Additionally, pelleted treatments containing micronutrients demonstrated variable effects, with some combinations resulting in phytotoxicity under dry soil conditions. These findings suggest that the integrated use of dense planting and bioactive seed coatings, particularly those containing growth regulators or fungicide-insecticide combinations, can significantly enhance sunflower stand establishment, yield, and physiological performance. Such integrative strategies hold promises for improving the sustainability and resilience of sunflower production systems under field conditions.