Improving sunflower yield through optimized nitrogen application scheduling in salt-affected coastal soils

Sunflower (Helianthus annuus L.) is a promising oilseed crop for the saline-prone coastal regions of Bangladesh; however, its productivity remains low due to inadequate, non-site specific nitrogen (N) management strategies. Despite evidence that split N application can improve nutrient use efficiency, there is limited information on the optimal timing and rate of N application for sunflower under salt-affected coastal soils, where nutrient dynamics are highly constrained. This study evaluated the hypothesis that synchronizing N application with critical growth stages would enhance yield and physiological performance under saline condition. A factorial randomized complete block design was employed at the Ganges delta during the 2023 and 2024 winter seasons, comprising three N application schedules (P1: Half as basal broadcast (BB) + quarter at 25 days after seed sowing (DAS) as side dressing (SD) + quarter at 45DAS as SD; P2: Half at 15DAS as SD +quarter at 30DAS as SD + quarter at 45DAS as SD; P3: One-third at 15DAS as SD + one-third at 30DAS as SD + one-third at 45DAS as SD) and three N rates (63, 84, and 105 kg N ha⁻¹), replicated thrice. Results revealed that both N timing and rate significantly influenced yield and associated traits. Equal split application at 15, 30, and 45DAS produced the highest grain yield (3.23–3.60 t ha⁻¹) and straw yield (6.60–8.75 t ha⁻¹), while 105 kg N ha⁻¹ consistently outperformed lower doses in enhancing seed number per head, 1000-seed weight, head diameter, and chlorophyll content. Strong positive correlations between seed yield and key yield traits further highlighted the importance of balanced N supply. The findings demonstrate that conventional basal application is suboptimal under saline conditions and provide new evidence that precise split application improves N use efficiency and crop productivity. Therefore, applying 105 kg N ha⁻¹ in three equal splits at 15, 30, and 45DAS is recommended as an effective, site-specific strategy for enhancing sunflower yield in coastal saline soils.