Growth and productivity of energy poplar plantations in Prykarpattia

Abstract

Purpose. To determine the optimum density and efficiency of fertilizer application to ensure the high productivity of the energy plantations of the 'Max-4' poplar on the sod podzolic soils of the Prykarpattia region. Methods. Field, laboratory, statistical. Results. After the fourth year of vegetation, the highest height of trees in the poplar plantations was recorded in the version with the lowest planting density (5.6 thousand plants/ha), 8.9 and 9.3 m, respectively. The average diameter of the central shoot was 109 mm at the control and 112 mm with fertilization at the rate of N40P300K300 + N40. It was found that the growth of the poplar of the fourth year of vegetation in height was slightly higher than the indicators of the third vegetation period, and lower in diameter. The diameter with the highest density (8.3 thousand plants/ha) was reduced to 9 and 12 mm per year. The average growth of these plantations in height over the last 2 years was at the level of 2.1 m, and in individual variants, it significantly increased from 1.7–1.9 m to 2.2–2.5 m. The highest yield of 4-year biomass was obtained at a density of 6.7 thousand plants/ha_ 69.5 t/ha of dry weight, which is 5.6 t/ha more than at a density of 8.3 thousand plants/ha and 2.9 t/ha compared to a density of 5.6 thousand plants/ha. The introduction of mineral fertilizers provided an increase in the yield by 12.9–16.2 t/ha of dry weight. According to the variants of the experiment, the average annual growth of dry biomass in the 4 years was from 12.8 to 17.7 t/ha, while in the fourth year it was from 11.2 to 15.6 t/ha. This indicates the feasibility of conducting the first harvest of poplar energy biomass after four years of cultivation. With the harvesting of poplar biomass after the third year of vegetation, a considerable amount of dry biomass (from 9.0 to 12.4 t/ha) can be obtained already in the first year. The introduction of mineral fertilizers ensured an increase in energy yield for all the studied density variants ranging from 227.0 to 285.1 GJ/ha. Conclusions. On turf podzolized medium-loamy soils of the Prykarpattia region, the highest indicators of the biomass productivity were found at the average planting density (6.7 thousand plants/ha) and fertilizer application. The biomass yield was 69.5 t/ha of dry weight, which is 8.8 % more than at the planting density of 8.3 thousand plants/ha and 4.4 % more than at the density of 5.6 thousand plants/ha. The optimum age of the first biomass harvesting in the studied density range is 4 years, and the next harvesting should be carried out every 3 years.