Willow plants (Salix viminalis L) were fertilized with a corn. synthetic fertilizer (up to 1.0 g/plant) and then with water-suspended diatoms (Navicula sp.) (600 000 cells in 1 mL of water, sonification at 20 Hz for 15 min, foliar application). The use of diatoms resulted in an increase in the quantity of microelements in plants (N, P, K) but did not affect their energetic properties (heat of combustion, calorific value and ash content) in the working state. The diatoms showed perspective potential as a new generation biofertilizer in prodn. of energy willow.