Abstract
In a strict field experiment we have studied the influence of various doses of nitrogen fertilization (0, 100, 175 kg N per ha) on the species composition and the number on weeds occurring in a field of winter wheat, cultivated on humus fertile soil. The optimum nitrogen dose for wheat (100 kg N per ha) did not cause vast differences in the weed community, in comparison with a control (without fertilization with N). However, its enlargement to 175 kg N per ha limited the number of species witch invested wheat with weeds, causing at the same time the compensation of nitrophilus species.