Productivity of sweet sorghum (Sorghum saccharatum L.) depending on the elements of plant сultivation technology for biofuel in the zone of insufficient moisture in the Forest-Steppe of Ukraine

Purpose. To reveal the influence of harvest timing of biomass of sweet sorghum various varieties and hybrids on their productivity and biofuel yield in the zone of insufficient moisture in the Eastern Forest-Steppe of Ukraine. Methods. Biological (conducting field research during 2017–2020) and statistical (descriptive statistics, analysis of variance, correlation and regression analyzes). Results. The lowest yield of sweet sorghum green biomass was during harvesting in early August. In ‘Sylosne 42’ and ‘Favoryt’ varie­ties it was 52.6 and 61.1 t/ha, in ‘Medovyi F1’ and ‘Dovista’ hybrids – 76.3 and 77.7 t/ha, respectively. The postponement of harvesting to mid-September allows increasing the yield of varieties ‘Favoryt’ and ‘Sylosne 42’ to 97.1 and 103.5 t/ha, ‘Dovista’ and ‘Medovyi F1’ hybrids up to 146.6 and 132.9 t/ha, respectively. With even later harvesting periods, an increase in the yield of green biomass was observed only in ‘Dovista’ (up to 152.5 t/ha). In the full ripening phase (BBCH 92–98), sugar sorghum plants accumulate the maximum amount of sugars in the sap. The highest cap sugar content was in plants of ‘Medovyi F1’ hybrid – 17.5%, in the other studied cultivars it varied from 14.8 to 15.5%. The hi­g­hest yield of biofuel and energy per unit area was achieved with gro­wing ‘Dovista’ (up to 815.8 GJ/ha) and ‘Medovyi F1’ (up to 792.0 GJ/ha) hybrids. Despite the high level of plasti­city, ‘Favoryt’ variety is inferior in total energy yield (up to 547.2 GJ/ha). ‘Sylosne 42’ has the lowest plasticity index (b = 0.79); however, it is the most stable variety, which allows to obtain a stable, though not high, energy yield (up to 559.6 GJ/ha). Conclusions. In the zone of insufficient moisture in the Eastern Forest-Steppe of Ukraine, the hi­ghest productivity indicators and the maximum energy potential can be provided by the hybrids of sweet sorghum ‘Dovista’ and ‘Medovyi F1’ for their harvesting not earlier than the phase of full maturity