Grain quality of grain sorghum hybrids as affected by plant density and growth regulator application in the Northern Steppe of Ukraine

Purpose. To determine the іnfluence of hybrid factor, plant density, and plant growth regulator application on protein and starch content and grain weight per liter in the Northern Steppe of Ukraine. Methods. The study was conducted under the conditions of insufficient moisture in the Northern Steppe of Ukraine from 2022 to 2024. The research methods included: field observations to monitor phenological stages and assess the impact of studied factors on grain sorghum yield; tabular method for data systematization, arrangement, and presentation; graphical method for visualizing research results. The scientific program aimed to study the influence of technological elements on phenological, biometric, structural-morphological indicators, and grain sorghum yield. To achieve the objective, a three-factor experiment was designed: hybrid (different maturity groups of grain sorghum hybrids − ‘Kalatur’, ‘ES Alize’, ‘ES Foehn’, ‘Albanus’, and ‘ES Musson’; plant density (170, 200, and 230 thousand plants per hectare); growth regulator (growth regulator ‘Appetizer’ applied at the 4–5 and 7–8 leaf stages at a rate of 0.5 l/ha with a working solution of 150 l/ha). Results. Over years of research, the highest average protein content in grain was observed in the mid-early hybrid ‘ES Foehn’ (11.4%) at plant densities of 170,000 and 200,000 plants/ha with the application of the growth regulator Appetizer and in the early-maturing ‘Albanus’ (12.0%) under similar conditions. The highest starch content (72%) among the studied hybrids was recorded in the mid-early hybrid ‘ES Musson’ at a plant density of 170,000 plants/ha with the application of the growth regulator. The highest grain weight per litre (750 g/l) was found in the mid-early hybrid ‘ES Foehn’ at a density of 170,000 plants/ha with the use of Appetizer. Overall, plant densities within the range of 170,000–200,000 plants/ha ensure high-quality sorghum grain. Conclusions. Plant densities within the range of 170,000–200,000 plants/ha ensure high-quality sorghum grain. Conversely, increasing plant density to 230,000 plants/ha leads to a decline in grain quality. The growth regulator Appetizer has a minor impact on starch content and grain weight per litre but can be considered as an adaptive element of cultivation technology aimed at increasing protein content and improving biometric and structural-morphological characteristics of plants.