Muzyka O. Yield formation of sugar sorghum as an energy crop in the Right-Bank Forest Steppe.

The dissertation deals with theoretical generalization and practical application of a research task that is to find out peculiarities of plant development and the formation of high productivity of mid-early and mid-late ripening sugar sorghum hybrids grown as energy crops for biofuels with different row spacing and plant density under the effect of growth regulators. For the plant density of 250 000 plants/ha, row spacing of 45 cm and using seeds treated with growth regulator Vympel 2 (0.5 L/t) + foliar application in the tillering stage (0.5 L/ha), the highest yield of green biomass in ‘Dovista’ hybrid was 98.8 t/ha, that was 5.3 t/ha lower than in ‘Huliver’ hybrid. Seed treatment with Vympel 2 (0.5 L/t) + foliar application in the tillering stage (0.5 L/ha) resulted in the gap in the yield of dry matter from 1.3 to 4.3 t/ha in the control treatment with a row spacing of 45 cm and varying plant density. For row spacing of 70 cm, the yield gap ranged from 1.2 to 3.5 t/ha. Similarly, in ‘Huliver’ sowings with a row spacing of 45 cm we obtained a yield increase from 1.7 to 3.9 t/ha and with a row spacing of 70 cm from 1.3 to 3.0 t/ha. When using the seeds treated with growth regulator Vympel 2 (0.5 L/t) + foliar application in the tillering stage (0.5 L/ha), an increase in the total sugar content from 0.6 to 0.8% in ‘Dovista’ compared to control treatment was obtained with row spacing of 45 cm and varying plant density and in an increase from 0.6 to 0.7 % for row spacing of 70 cm. In the same way, in ‘Huliver’, for the use of seeds treated with growth regulator Vympel 2 (0.5 L/t) + foliar application in the tillering stage (0.5 L/ha) for the row spacing of 45 cm, these values ranged from 1 to 1.0 % with row spacing of 45 cm and from 0.5 to 0.9 % with row spacing of 70 cm. The maximum values of energy yield were obtained for the row spacing of 45 cm, plant density of 250 000 plants/ha and use the seed treated with growth regulator Vympel 2 (0.5 L/t) + foliar application in the tillering stage (0.5 L/ha). In ’Dovista’, the increase in energy yield was 457.35 GJ/ha and in ‘Huliver’ it was 467.82 GJ/ha. To sum up, the highest profit of growing ‘Dovista’ and ‘Huliver’ hybrids was obtained for the row spacing of 45 cm, plant density of 250 000 plants/ha and with the use of the seed treated with growth regulator Vympel 2 (0.5 L/t) + foliar application in the tillering stage (0.5 L/ha), 29225 UAH and 26635 UAH, respectively. The profitability of such agronomic practices was the highest and amounted to 156.3 % in ‘Dovista’ and 142.4 % in ‘Huliver’. Keywords: sugar sorghum; growth regulator; yield; yield structure component; products; energy efficiency; economic efficiency.