Radiation and Photothermal Coefficient as Major Determinants of Grain Yield and Oil Content in Sunflower under Different Sowing Dates

Abstract

Environmental conditions throughout the sunflower life cycle affect its phenological and physiological aspects, influencing growth and development, and ultimately, grain yield and oil content. While numerous studies have clarified the effects of specific environmental factors on sunflower oil yield and its components, a comprehensive understanding of how combined environmental conditions influence sunflower productivity requires research conducted under real production conditions. Given that different sowing dates expose the crop to varying environmental conditions, this study investigated the effects of three contrasting sowing dates and the underlying environmental conditions on sunflower grain yield, oil content, and oil yield. A broad set of commercial hybrids was evaluated using a randomized complete block design with four replicates across five environments (year or geographic location) in central Argentina. The sowing date was the major source of variation in grain yield, oil content, and oil yield, accounting for 57.2, 62.9 and 62.6% of the total variation, respectively. Sunflow-ers sown in early spring exhibited significantly higher grain yield and oil content compared to those sown in late spring or early summer, which resulted in 22.3 and 39.1% lower grain yield and 2.6 and 11.3% lower oil content, respectively. Solar radiation and the photothermal coefficient during grain filling were the major environmental factors influencing sunflower parameters. Surprisingly, genotype and its interactions accounted for less than 2.7% of the variation in sunflower oil yield. This study enhances our understanding of how integrated environmental factors impact sunflower grain yield, oil content, and total oil yield.