Grain sorghum is a drought-resistant crop and forms a high grain productivity and biomass as a raw material for the production of bioethanol and solid fuel in difficult soil and climatic conditions.
The aim of the research was to establish the influence of sowing seeds method of the grain sorghum varieties on the photosynthetic activity of crops in the conditions of the Right-Bank Forest-Steppe of Ukraine.
Methods. Field, laboratory, mathematical and statistical. Results. It has been proved that the leaf surface area of grain sorghum plants reached its maximum during the period of "throwing out panicles - flowering". It was the largest when sowing with a row spacing of 45 cm and at a plant density of 150 thousand units/ha – 34.8 thousand m2/ha for the Dniprovsky 39 variety and 32.7 thousand m2/ha for the Vinets variety. With the standing density of 200 thousand pieces/ha, the Dniprovsky 39 variety has 37.8 thousand m2/ha, the Vinets variety – 35.6 thousand m2/ha and with the density of 250 thousand pieces/ha, respectively 38.2 and 36.9 thousand m2/ha. The photosynthetic potential also changed depending on the size of the assimilation surface during the growing season. It was the highest when sowing seeds with a row spacing of 45 cm and amounted to 1.13–1.29 million m2/ha for the Dniprovsky 39 variety and 1.10–1.22 million m2/ha for the Vinets variety. When sowing with the row spacing of 15 cm, this indicator was 0.86–1.07 million m2/ha for the Dniprovsky 39 variety and 0.84–1.09 million m2/ha for the Vinets variety. When sowing grain sorghum seeds with the row spacing of 70 cm, the photosynthetic potential was 0.83–1.03 million m2/ha and 0.78–0.95 million m2/ha, respectively.
An increase in the plant density from 150 to 250 thousand pieces/ha of grain sorghum contributed to an increase not only in the assimilation leaf surface, but also in the photosynthetic potential. The high net productivity of photosynthesis was observed when sowing seeds with the row spacing of 45 cm and for the Dniprovsky 39 variety it was in the range of 3.36–3.94 g/m2 per day, for the Vinets variety — 3.32–3.81 g/m2 in day.