ENERGY WILLOW (Salix L.) PLANTATION PRODUCTIVITY UNDER THE CONDITIONS OF THE CENTRAL FOREST-STEPPE OF UKRAINE

Abstract

Introduction. Reducing the dependence of the economy on imported fossil fuels is a critical problem in Ukraine. Renewable energy sources, in particular, wood take a large part in solving this problem [1, 2, 3, 4, 5, 8]. Limited opportunities for energy wood from forest plantations encourage searching other ways of obtaining the wood, specifically growing it on dedicated energy plantations. Due to the specific biological and ecological characteristics, several species and varieties of willows are often cultivated on such plantations. The purpose of the research was to study the specifics of growth and productivity of energy plantations of two willow varieties, namely basket willow (Salix viminalis L.) [1] and almond willow (Salix triandra L.) on leached black soil in the Central Forest-Steppe of Ukraine and to find out the optimal frequency of biomass harvesting.

Methods. The study was carried out from 2013 to 2015 in the test field of IBC&SB in Vasylkiv district (Kyiv region). In early September 2013, the site was treated with non-selective herbicides followed by a thorough tillage. Willow cuttings 20 cm long 10-15 mm in diameter were planted in two periods: late September and late October. Along with the cultivation, weeds in the rows were earthed. Acting in this way helped us to kill 50-60% weeds.

At the end of each growing season, we determined the survival of plants, their dimensions and weight. The height of the bushes and the diameter of the highest shoot in a bush were determined at the end of each month during growing season. A part of plantation was cut off before the third growing season to find out the feasibility of a two-year harvest cycle. We used convenient research methods. Measuring the bush height was carried out using a ruler (to within 1 cm), and the diameter of the largest shoot in a bush using electronic calliper (to within 0.1 mm). The data was processed on a PC using Statistika software.

Results and discussion. Planting in late September provided 85 % establishment of almond willow cuttings and 92 % of basket willow, while conducted in late October, 87 and 80 %, respectively. In subsequent years, dying-off of plants in plantations was insignificant. The most intensive growth of plants in the second year of cultivation was observed during the summer months, and the cessation of growth took place in early October. Currently, basket willow shrubs have an average height of 254 cm and almond willow 191 cm. The annual increase in height was 160 cm and 123, respectively. In the third growing season, growth rates of willow in the plantations under study were even greater. To illustrate this, basket willow’s increase was 181 cm, and almond willow’s one 164 cm. In this case, the average height of a three-year plants in experimental plantations of basket willow when planting cuttings in September and October, amounted to 4.4 ± 0.12 and 4.3 ± 0.16 m, and in almond willow 3.5 ± 0.14 m and 3.6 ± 0.16 m, respectively.

The maximum green mass (54.6 t/ha) was produced in plantations of basket willow planted in late September. In almond willow, this figure was 27.7 t/ha. Slightly lower productivity was in plantations of basket willow established at the end of October (32.3 t/ha), while productivity of almond willow in this treatment was higher compared with planting in September and amounted to 30.9 t/ha.

Fairly high productivity was observed in the treatment, where bushes were cut after the second year of cultivation (in spring 2015). In this treatment we obtained 29.2 t/ha of green mass in basket willow plantation and 26.4 t/ha in almond willow plantation. During the growing season of 2015, two-year old bushes of basket willow grew to an average height of 3.2 ± 0.14 m, while basket willow to 2.7 ± 0.12 m, providing wood mass of 14.7 and 12.7 t/ha, respectively.

Conclusions. The success of growing energy willow feedstock depends on the optimal combination of species, soil and climatic conditions and farming practices; therefore, the actual problem is the choice of high-yielding species and forms of willows and effective technological schemes of growing plantation adapted to specific soil and climate conditions of Ukraine.

In leached black soil of the Central Forest-Steppe, planting in early autumn (late September) provided a higher survival rate of almond willow (85%) and basket willow (92%) than planting in early October (80% and 87%, respectively). In subsequent years, dying-off of plants in plantations was insignificant and had no sizeable effect on productivity.

For the most complete killing weeds and reducing the need for manual labour, it is appropriate to earth weeds in the rows along with the cultivation. This practice allows killing about 50-60 % of weeds.

Given two-year harvest cycle, the total productivity of three-year plantations of almond and basket willow was almost identical (41.1 and 41.9 t/ha, respectively). Three-year harvest cycle ensured yield of 54.6 t/ha in basket willow, that was much higher than yield of almond willow (27.7 t/ha). This leads us to a preliminary conclusion that in the early years of growing basket willow under the conditions of studied region it is appropriate to use the three-year harvest cycle and while for almond willow two-year harvest cycle is feasible.

In a production environment, taking into account the weather conditions, marketing and logistics, both two-year and three-year harvest cycle can be considered appropriate to produce feedstock of both energy willow species.