The experiments were conducted in 1998-2000 at the Research Station in Wierz- chucinek, belonging to the University of Technology and Life Science in Bydgoszcz. The two-factor field experiment was made and the effect of diverse nitrogen dosages (0, 60, 120, 180 kg N∙ha^-1) on the content of total nitrogen and amino acid composition was analysed in the consecutive plant growth phases. Nitrogen fertilization significantly reduced nitrogen content in the green mass of winter barley in each phase of its growth. An essential decrease in the contents of the most exogenous amino acids was shown, which may suggest some decline in the protein biological value.

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