Two energy plants – common osier (Salix viminalis L.) and black poplar (Populus nigra L.) – were investigated in order to evaluate their productivity, to perform an energy growing analysis and to investigate plant physical-mechanical and energetic properties of chopped plants for biofuel production. The field experiments were conducted at the Vėžaičiai branch of the Lithuanian Research Centre for Agriculture and Forestry (Western Lithuania, 55°43′N, 21°28′E). The average common osier’s yield was 7720 t ha^-1 of dry matter (DM), and that of black poplar was 4228 t ha^-1 DM. A 3.0 t ha^-1 liming rate and 60 kg ha^-1 N rate was optimal for both crops growth and DM productivity.

   Common osier and black poplar chaff`s elemental composition analysis showed a similar C (carbon) content of 49.1–49.7%, H (hydrogen) content of 5.6–5.8%, N (nitrogen) and S (sulphur) in small volume %. The estimated ash content of the investigated plants was relatively low – from 1.44% for willows to 2.52% for poplars. The lower calorific value of these plants’ dry chaff was relatively high (18.49–18.62 MJ/kg). Depending on the different liming and nitrogen fertilization rates, the total energy input (including direct and indirect inputs) to the growing process constituted 8.41–29.21 GJ ha^-1. Common osier had the highest energy output (from 1030 to 1639 GJ ha^-1) and the highest energy use efficiency (46.01–122.47).

   Keywords: black poplar, biofuel, elemental analysis, calorific value, common osier, energetic evaluation