Sowing Date Effects on Sunflower Productivity and Seed Quality Under Rainfed No-Till Conditions in the Dobrogea Region of Romania

Climatic variability and recurrent drought increasingly threaten rainfed sunflower production in south-eastern Europe, highlighting the need for practical adaptation strategies. This study evaluated the effects of two sowing dates, early sowing on 24 March (SD1) and conventional sowing on 14–15 April (SD2), corresponding to the common sowing practice in the region, on sunflower productivity and seed quality during three consecutive growing seasons (2023–2025) under rainfed no-till conditions in the Dobrogea Region of Romania. A randomized complete block design with three replications was used, while all agronomic practices remained identical except for sowing date. Crop performance was assessed through yield, oil content, plant density, plant height, seed weight per capitulum, thousand-grain weight (TGW), test weight, and seed moisture, and data were analyzed using ANOVA, Student’s t-test, Pearson correlation, and redundancy analysis (RDA). Early sowing resulted in higher mean values than conventional sowing, increasing seed yield by 25.4% (1341.65 vs. 1070.20 kg ha−1), oil content from 44.80% to 45.90%, TGW from 47.39 to 53.96 g, test weight from 37.46 to 41.64 kg hL−1, and seed weight per capitulum from 34.45 to 38.72 g. The magnitude of the sowing-date response varied among growing seasons, highlighting the importance of considering naturally occurring interannual variability when interpreting treatment effects. RDA indicated that precipitation showed the strongest association with variation in agronomic performance. Advancing sowing by approximately three weeks was associated with improved crop performance across the three growing seasons, which were characterized by naturally occurring interannual meteorological variability. These findings provide site- and hybrid-specific evidence to inform sowing-date decisions for rainfed no-till sunflower production.