The example of various varieties and hybrids of sugar sorghum illustrates the summary of study on assessing varying density of plants in crops on phonological cha­racteristics of sugar sorghum plants, carbohydrate composition of sorghum juice and yield of its plants. The completed study established that one hectare of sugar sorghum, subject to varietal characteristics and varying density of plants in crop, may provide the green weight of 40.83 до 106.87 t/ha at stem juice yield of 22,27 to 56,24 t/ha, which would contain 2.31 to 6.09 t/ha of total sugars suitable for bioethanol production in at the rate of 198.25 to 501.19 dal/ha. However, despite of higher estimate of total sugars yield and bioethanol at 300 thousand plants per ha density in crop, industrial plots would preferably have plant density in crops ranging within 200...250 thousand pieces per ha. Since higher density increases dry matter content of plants, consequentially, cellulose and lignin in stems, this may create preconditions for harvest losses due to stem lod­ ging Besides, 200 thousand plants per hectare enables to reach the highest level of photosynthesis net productivity which combines high intensity of the photosynthesis with photosynthetic activity of leaf surface.

Purpose. This study was aimed to determine some biochemical parameters and productivity of the gene fund of Silphium L. genus in the M. M. Gryshko National Botanical Garden of the NAS of Ukraine. Methods. Plant raw material investigated at the flowering stage (17 genotypes) and the end of vegetation (20 genotypes) of Silphium spp. 3 species and 4 cultivars studied for the content of nutrients at the flowering. Determination of dry matter, ash, calcium, nitrogenfree extractives conducted according to Hrytsaienko et al. (2003), phosphorus, protein – according to Pochinok (1976), sugars – according to Krishchenko (1983), cellulose – according to Zheng et al. (2018), lipids – according to Zamowski, Suzuki (2004). It was used productivity parameters: yield of above-ground mass, the yield of dry mass, energetic value, yield of energy. Data analyzed statistically. Results. Investigation of nutrients content showed that content of dry matter was in the range of 18.90–29.3%, protein – in the range of 8.88–23.56%, cellulose – 15.10–36.14%, ash – 8.13–12.19%, lipids – 1.83–3.97%; yield of above-ground mass – 45.0–139.0 t/ha, the yield of dry matter – 10.31–36.92 t/ha, energy value – 3933–4249 cal/g, and yield of energy – 43.81–149.27 Gcal/ha. A study of genotypes at the flowering and end of vegetation identified that the content of dry matter for all samples was in a range of 18.38–67.49%, sugars – 2.78–19.0%, ash – 3.93–11.20%, calcium – 1.68–5.99%, phosphorus – 0.14–1.21%, energy value – 3153.36– 3770.28 cal/g. Conclusions. Plant raw material of genotypes of Silphium L. spp. is a valuable source of nutrients. The content of ash, its components, energetic value, and parameters of productivity depending on genotype and stage of growth. The results allow recommending selected Silphium genotypes as perspective energetic crops in Ukraine as well as other countries.