The investigations with oat plants were carried out on highmoor peat in pot experiment. The experiment comprised 5 series differing in the period of copper fertilization. The solution of copper sulfate was applied after germination, at the stage of tillering, shooting or earring. Samples of oat were collected four times in the period of experiment. It was found that fertilizing and period of application considerably differentiated yields of oat at the stage of tillering and shooting. The most intensive copper intake took place from the stage of germination till the tillering phase and at the end of vegetation. The level of copper in oat influenced on the content of nitrogen.