Productivity of poplar energy plantations on low-humus chornozems (black soils) of the Right-Bank Forest-Steppe of Ukraine

Abstract

Depletion of fossil energy deposits against the background of intense growth of the world's energy needs creates prerequisites for searching alternative renewable energy sources, among which the biomass of woody plants is considered one of the most promising. The purpose of the studies was to determine the growth characteristics of a medium-rotation energy plantation of poplar variety 'Robusta' in the conditions of the Right-Bank Forest-Steppe of Ukraine on leached chornozems during the first four years. The plantation was established with one-year-old lignified cuttings 25 cm long and 0.8-1.0 cm in diameter in two density variants. Planting spacing – 2.0×0.8 m and 2.0×0.9 m. After the first year, trees at both sites averaged 1.6 m in height. During the second year, their height increment was 2.0±0.05 m for the plantation variant of wider spacing and 2.1±0.05 m for the denser one. During the third growing season, the height increment was 3.1 and 3.0 m, respectively, and the average height of the plants was 6.8 and 6.6 m, respectively. During the fourth growing season, the height increment slowed down significantly (to 1.2 and 1.1 m, respectively) and the average height of four-year-old plantations was 8.0±0.16 m in the variant of denser spacing and 7.7±0.22 m in the variant of wider spacing. At the end of the first year of cultivation, the diameter of the stems at a height of 1.3 m (diameter at breast height) was greater in the denser spacing (0.5 versus 0.3 cm), but already during the next year, the trees became 2 mm thicker in the variant of less dense spacing. A similar trend persisted in the third year, when the average diameter of trees of the denser variant was 5.8 cm, and that of the variant of wider spacing – 6.2 cm. In the fourth year of cultivation, the diameter increment in both plantations decreased significantly (to 1.4 and 1.8 cm, respectively) and their average diameter reached 7.2±0.22 and 8.0±0.31 cm, respectively. After three years of cultivating a poplar plantation created by cuttings, 11.66-14.58 tons of dry biomass, or 207.5-259.5 GJ of energy can be obtained per hectare. After four years, the productivity of such plantations increases sharply (from 25.78 to 29.94 t/ha, or from 458.8 to 532.8 GJ/ha). A significant increase in the biomass yield of energy plantations of poplar variety 'Robusta' during the fourth year of cultivation indicates the advisability of using a 5-7-year period of cultivation of such plantations to obtain the maximum amount of biomass. The positive results of rooting cuttings 20-25 cm long in the study region indicate the similarity of the general elements of poplar cultivation technology, which are used in different regions of the northern hemisphere. The results obtained correlate with the studies of other authors, who focus on the advisability of using poplar cuttings 20 cm long. The results of studies on planting time indicate the possibility of obtaining positive results from the rooting of poplar cuttings and a good growth of one-year-old rooted cuttings both during spring and autumn planting.

Keywords

• populus l.; bioenergetics
• variety 'robusta'
• cuttings
• rooted cuttings
• average height
• average diameter
• yield of energetic biomass