The dissertation presents the theoretical justification and results of experimental studies on the direct impact of mineral fertilizer rates and retardants on sunflower productivity, as well as the search for potential synergistic effects of these factors when combined.
During the research years, there was a significant increase in temperature with an insufficient and uneven distribution of precipitation.
It was found that the water consumption coefficients of sunflower plants for the formation of 1 ton of dry matter varied by year and experimental variant, as they depended on moisture availability during the plant vegetation period and the accumulated dry matter of sunflower hybrids.
The amount of precipitation during the research years was characterized by the following indicators: 2489 m³/ha in 2021, 1923 m³/ha in 2022, and 2963 m³/ha in 2023. Moisture consumption during the vegetation period was calculated to be 2533–3645 m³/ha.
It was found that the highest water consumption coefficient per 1 ton of sunflower seeds was obtained in 2023. For the RGT Wolff hybrid, it varied with increasing fertilizer rates from 1664 to 996 m³/t, for Alzan – 1672–1108 m³/t, for ES Bella – 1796–1187 m³/t, and for Lime – 1727–1115 m³/t.
It was found that the maximum leaf area parameters of sunflower hybrid crops were formed at 64-68 microstages of development according to the BBCH scale.
It was determined that the highest chlorophyll content in sunflower plants was at 64-68 BBCH microstages (chlorophyll a content ranged from 4.49 to 6.79 mg/1 g of dry matter, and chlorophyll b from 1.66 to 2.24 mg/1 g of dry matter). The maximum values were achieved in the RGT Wolff hybrid in the variant with the application of N120P80K180. The application of the retardant Setar caused a decrease in chlorophyll content at the initial stages of development and an increase, starting from 54-58 microstages of development according to the BBCH scale, compared to the variants without its application.
It was established that the application of fertilizers influenced the height of sunflower plants. In the RGT Wolff hybrid, with the increase in fertilizer rates, the height increased from 150.7 to 175.2 cm, in Alzan from 145.6 to 169.6 cm, in ES Bella from 145.9 to 169.9 cm, and in Lime from 136.1 to 163.8 cm
It was found that the stem diameter of sunflower plants varied over the research years due to the genetic characteristics of the hybrids, fertilization, and the effect of the retardant. The maximum stem diameter was obtained in all sunflower hybrids we studied in the variant with the application of the maximum fertilizer dose – N120P80K180, with values ranging from 3.13 to 3.26 cm.
It was found that the dry matter weight of individual sunflower plants increased with higher fertilizer rates used, reaching maximum values in the variant with N120P80K180 application. In the RGT Wolff hybrid, the dry matter weight per plant averaged over the years of research varied from 113.0 to 188.9 g/plant.
It was observed that increasing fertilizer rates resulted in an increase in the head diameter of plants across all hybrids studied. The application of the retardant also contributed to an increase in head diameter by 0.1–0.5 cm depending on the hybrid and fertilizer rates.
It was established that the sunflower hybrids produced yields influenced by fertilizer variants and the effect of the retardant. On average over the years of study, yields per hectare were as follows: RGT Wolff hybrid – 2.14-3.74 tons/ha, Alzan – 2.09–3.40 tons/ha, ES Bella – 2.06–3.23 tons/ha, Lime – 2.03–3.31 tons/ha.
Calculation of the contribution of factors to the productivity of sunflower hybrids in the study showed that the variants of fertilization had the greatest impact at 48.7%, followed by the genetic characteristics of hybrids at 13.7%, treatment with the retardant at 4.8%, and weather conditions during the years of the study at 15.8%.
It was found that the fat content in sunflower seeds depended on the genetic characteristics of the hybrids, fertilization, the influence of the retardant, and the weather conditions during the vegetation period of sunflower. In the RGT Wolff and Alzan hybrids, an increase in fertilizer dose up to N80P50K120 resulted in an increase in fat content.
The maximum oil yield was achieved in the cultivation of the RGT Wolff hybrid with the application of N100P65K150 and the use of the retardant Setar – 1.74 tons per hectare.
It was determined that the production costs for cultivating sunflowers in farm conditions, excluding costs for mineral fertilizers, hybrid seeds, and retardants, amounted to 10,998 UAH per hectare. The maximum profit was obtained in the cultivation of the RGT Wolff hybrid with the application of N100P65K150 and the use of the retardant Setar – 27,804 UAH per hectare.
