The Effect of Sowing Dates and Seeding Rates on Sunflower Productivity Under the Conditions of Southern Ukraine

The article presents the results of research on the impact of sowing dates and seeding rates of viable seeds per hectare on the productivity and quality indicators of sunfl ower under the conditions of southern Ukraine. Purpose of the study – to determine the optimal sowing dates and seeding rates of viable seeds for sunfl ower cultivation in southern Ukraine, which ensure effi cient use of solar radiation and nutrients, contributing to higher yields and improved seed quality. Methods. The experiment involved fi eld, gravimetric, visual, laboratory, computational-comparative, and mathematical-statistical methods, based on widely recognized methodologies and guidelines. Results. The early-maturing hybrid "Carlos 105" was used in the trials, sown at different times with seeding rates of 30, 40, and 50 thousand viable seeds per hectare. The highest sunfl ower yield was achieved under recommended sowing dates, when soil temperature reached 10-12°C, combined with a seeding rate of 40 thousand viable seeds per hectare. Under these conditions, plants formed well-fi lled seed heads, and showed high 1000-seed weight and oil content. Early sowing (at 6-8°C) resulted in slower initial growth and a higher risk of frost damage to seedlings, whereas late sowing (at 14-16°C) shortened the growing season and reduced productivity. Phenological observations showed that the timing of developmental phases varied depending on the sowing date: early sowing extended the vegetation period, whereas late sowing shortened it. Additionally, the infl uence of weather conditions in each year had a signifi cant effect on the realization of yield potential. Conclusions. The study on the effect of sowing dates and seeding rates on biometric indicators and sunfl ower yield revealed that the recommended sowing period, when the soil temperature reaches 10-12°C at a depth of 10 cm, and a seeding rate of 40 thousand viable seeds per hectare, ensures better plant growth and development, thus leading to higher yields. Deviations from these optimal parameters, whether due to earlier or later sowing, or changes in seeding rate (increase or decrease), led to reduced biometric parameters and potential yield.