The most often used substrate in agricultural biogas plants is maize. Due to an increase in the area of maize acreage and the necessity of use proper crop rotation in the plant cultivation, alternative raw materials should be looked for. Apart from the high biomass yield, alternative plants for biogas production should be characterized by a favourable energy efficiency index. The favourable value of this index can be obtained by reduction of energy outlays incurred for biomass production and high energy efficiency in the yield. The aim of this study was to compare the yield and energy efficiency of biomass production of some species of plants grown under different conditions of energy outlays. The study was conducted in the years 2009-2011 at the Production and Experimental Station at Bałcyny near Ostróda (53°35’ N; 19°51’ E) of the University of Warmia and Mazury in Olsztyn. The study was based on the strict two-factorial experiment established in soil of 4. soil agricultural suitability complex, where three plant species were compared (maize cv. LG 2244, sorghum cv. Sucrosorgo 506, Virginia fanpetals) cultivated according to two technologies – high-input (intensive) and medium-input (with reduced outlays for means of production in relations to the intensive technology). Among the studied plants, the highest efficiency of biomass (21.4 Mg⋅ha^-1 d.m.) and energy in yield (390 GJ·ha^-1) and the most favourable index of energy consumption per unit (1.02 GJ·t^-1) and energy efficiency (18.4) were provided by maize. Sorghum and Virginia fanpetals gave significantly lower yields than maize (by 40 and 54%, respectively) and were not equal in respect of energy discriminants in yield, energy consumption per unit or energy efficiency. The high-input technology provided a significantly higher biomass yield on average for 3 studied species (15.8 Mg⋅ha^-1 d.m.) than medium-input (13.6 Mg⋅ha^-1 d.m.). In the medium-input technology, reduction in energy outlays by 27%, mainly of mineral fertilization, caused a significant decrease in biomass yield by 14%, but it provided a higher energy efficiency of its production (15.3). The most favourable energy efficiency index of biomass production was obtained by maize cultivated in the medium-input technology (19.7). Lower energy assessment value of sorghum and Virginia fanpetals does not eliminate possibility of using the biomass of these plants as supplementing substrates for biogas production.

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