Peculiarities of plant growth, development, and chemical composition of the Paulownia biomass

Purpose. To establish the peculiarities of plant growth, development, and chemical composition of the paulownia biomass of two species in the Right Bank Forest Steppe of Ukraine. Methods. Field, laboratory, measuring and weighing, mathematical and statistical. Results. The biological properties of two Paulownia species, namely Clone in vitro-112 and Paulownia tomentosa, were studied. The maximum number of leaves per plant at the end of the vegetation season was 24–26 in Clone in vitro-112 and 22–24 in Paulownia tomentosa. Leaf area per plant was 5.0–5.5 m2 and 4.0–4.5 m2, respectively. The main period of wood accumulation falls during the first three years of vegetation, and during this period, biomass productivity indicators are the highest. Five-year wood yield per tree was about 0.35 m3 in Clone in vitro-112 and 0.24 m3 in Paulownia tomentosa. The research determined the optimal content of nutrients, the lack or excess of which negatively affects biomass quality. Nitrogen is mostly concentrated in leaves (2.3–2.6%) and petioles (0.67–1.1%). The content of phosphorus was quite low: 0.33–0.36% in leaves and 0.22–0.23% in petioles. Plants contain a significant amount of potassium in the leaves: 1.25% in Clone in vitro-112 and 0.75% in Paulownia tomentosa. Conclusions. Clone in vitro-112 can be recommended for cultivation in the Right Bank Forest Steppe Zone of Ukraine. One hectare can produce 200–250 m3 of industrial wood and the same amount of branch biomass for 5–6 years. Branches are suitable for the production of fuel pellets and chips with low ash content (0.8–1.5%). At the same time, leaves and petioles of paulownia have an increased ash content (3.9–7.1%) due to the higher content of nutrients, in particular nitrogen. Therefore, it is not advisable to use them as feedstock for the production of solid biofuel, but they are suitable for the production of biogas.