In the field experiment conducted in 2006–2008 years, the influence of harvest
number (one or two) and levels of nitrogen initial fertilization: (25, 50, 75, 100 kg N · ha–1 ) on
dry matter, calorific value, and ash of the Japanese knotweed plants was estimated. The
energetic effectiveness index was calculated, also. Application of initial nitrogen doses had no
significant effect on final dry matter yields of plants. Planning multi-year utilization of knotweed
as a renewable source of energy one harvest during autumn- winter time seemed to be best.
High biomass yields of Japanese knotweed (mean 9.84 t · ha–1) and great calorific value
(16–17 MJ · kg–1), indicate that is a possibility for utilization this plant as an energetic plant (Ee = 8.27).