Nine clones of willow were planted in the first decade of April 2005 in the experimental field of Koszalin University of Technology - in Kosciernica, on light soil of classes IVb-V, at a density of 33.2 thousand of seedlings per hectare. In 2006 strict experiment was established using method randomized sub blocks in the dependent system, with three replications, where sub blocks of I level were four combinations of fertilizers, and level II - nine willow clones. Plot area was 34.5 m(2) (2.3 x 15.0 m). Following clones of willow were included in the experiment: 1047, 1054, 1023, 1013, 1052, 1047D, 1956, 1018 and 1033, which marked respectively with letters: A, B, C, D, E, F, H and G. In the years 2006-2009 during willow vegetation biometric measurements were performed on 10 plants, including: height and thickness of stems and the number of shoots in the bush, in four terms (31 May, 30 Jun-31 Jul, 30 Aug and 10-30 Nov). Thickness of shoots measurements were performed at a height of 10 cm from the ground. The study evaluated regrowth of bushy willow shoots in four-year cycle in nine clones cultivated on light soil with application of compost from sewage sludge and different doses of Hydrofoska 16 fertilizer. In the region of Koszalin during willow vegetation period (April-October) in the years 2006-2009, precipitation was 459-654 mm, at annual quantities of 753-1062 mm. Under conditions of relatively good willow supply with precipitation water (annual precipitation >750 mm and in the period of April-October >450 mm), with a deep groundwater level, it was possible to obtain satisfactory length and thickness of shoots in subsequent years of cultivation, respectively: I - 141 cm, II - 269 cm, III - 313 cm and IV - 378 cm and I - 8 mm, II - 14 mm, III - 17 mm and IV - 24 mm. Willow clones were divided into groups in terms of response to fertilization, taking into account the annual increases in the length and thickness of stems. Little response to fertilization showed clone D, and large-clone F. The final classification of the clones in terms of fertilizer requirements will be achieved only after assessing the dry mass yield, since not all clones after harvest, after second vegetation, contained the same quantity of dry mass.
