Peculiarities of the formation of energy biomass by poplar plantations on the leached chernozems of the Central Forest Steppe of Ukraine

Purpose. To determine the energy biomass productivity of poplar variety 'Robusta' on leached chernozems of the Central Forest-Steppe of Ukraine during the first four years. Methods. Field, laboratory, and statistical. Results. The data of research on the growth of energy plantations of the 'Robusta' poplar variety during the first four years on leached chernozems of the Central Forest Steppe of Ukrainare presented. The plantation was established using one-year lignified 25 cm long cuttings that have a diameter in the upper section of 0.8–1.0 cm. The cuttings were planted according to two planting design: 2.0 × 0.8 m and 2.0 × 0.9 m. In both variants, at the end of the first vegetation season, the trees had an average height of 1.6 m. In the second vegetation season, the height increase in the first variant was 2 .0 ± 0.05 m, and on the second 2.1 ± 0.05 m. In the third year of cultivation, the growth of poplar trees reached the maximum height and amounted to 3.1 and 3.0 m, respectively, at the end of the year, with the average height of plants reaching 6.8 and 6.6 m, respectively. In the fourth year of vegetation, the increase in height slowed down significantly (to 1.2 and 1.1 m, respectively) and the average increase in plant height began to decrease significantly: their height was 8.0 ± 0.16 m in the first variant and 7.7 ± 0.22 m in the second. The average stem diameter of plants at a height of 1.3 m after the first year was higher in the first variant compared to the second (0.5 cm vs. 0.3 cm). However, already during the second year, the trees of the second (less dense) plantation increased their diameter by 2 cm. The same difference was preserved in the third year, when the average diameter of the trees of these variants was 5.8 and 6.2 cm, respectively. During the fourth growing season, the average increase in diameter in the studied plantations significantly decreased, and their average diameter indicators reached 7.2 ± 0.22 and 8.0 ± 0.31 cm, respectively. At the same time, there was a significant increase in the productivity indicators of such plantations at this time: from 25.78 to 29.94 t/ha, with energy yield ranging from 458.8 GJ/ha to 532.8 GJ/ha. This circumstance indicates the expediency of using a 5–7-year cycle of biomass harvesting on such plantations to obtain maximum productivity indicators. Conclusions. On the leached chernozems of the Central Forest Steppe of Ukraine, poplar energy plantations of 'Robusta' variety after three years of cultivation accumulate about 12–15 tons of dry biomass per 1 ha, and after four years from 26 to 30 tons of dry biomass per 1 ha. It is advisable to continue the study of the growth of such plantations in order to establish the optimal rotation of the coppice.