Growth and development of energy willow plantations of different density for the introduction of nitrogen fertilizers on the leached chernozems of the Central Forest-Steppe

Abstract

Purpose. Determine the optimal density and nitrogen fertilization rates to ensure the intensive growth and high productivity of energy plantations of some willow varieties under the conditions of the Central Forest-Steppe. Methods. The object of the study was the exploration of plantations of two willow varieties ( Salix viminalis L.), namely ‘Tora’ and ‘Ternopilska’, created under the conditions of the northern part of the Central Forest-Steppe of Ukraine in the spring of 2015. Willow twigs of 20 cm were planted in two pairs of rows with a distance between them 0.75 m for two variants of row spacing: 1.50 and 2.50 m. The planting density was 12, 15 and 18 thousand plant/ha. Results. After two years of growing willow, the average height of plants ranged from 339 to 493 cm. After the third year (2017), the height increase was less than the previous year. For planting schemes 0.75×1.50×0.75 m in ‘Tora’ variety, higher plants were in the variant with a planting density of 12 thousand plants/ha (553 cm), and for widths spaced 2.50 m at 18 thousand plants/ha (588 cm). In ‘Ternopilska’ variety, under both planting schemes, plant height was higher at the density of 18,000 plant/ha (452 and 414 cm, respectively). Before the beginning of the fourth vegetation period (2018), three years of the aboveground mass of willow was cut and ammoniac saltpeter was added to the part of the area in the amount of 35 and 70 kg a.i./ha. In both varieties, new coppice formed, which was characterized by a much larger number of shoots per bush, from 4.8 to 6.6 in ‘Tora’ and from 3.5 to 8.8 in ‘Ternopilska’. Their height after the first vegetation period was 398–477 and 283–425 cm respectively, that is approximately at the height of plants after the first two years of vegetation. There was a tendency to reduce the number of shoots in the bush and their height for increasing the density of plantings. The conducted researches indicate the positive influence of the introduction of ammonium nitrate in the norm of 70 kg a.i./ha on plant height and biomass productivity. Conclusions. Among the two used varieties of willow on the leached chernozem of the Central Forest-Steppe of Ukraine, ‘Tora’ variety was marked by more intensive growth and higher productivity. Better planting design for both varieties was 0.75×1.50×0.75 m. Since the density options selected for research yielded roughly identical results, the smaller ones should be considered suitable for use, i.e. 12 and 15 thousand plants per hectare. Used rates of ammonium nitrate, especially N 70 , contributed to the increase in the height of annual voluntary growth and biomass productivity.