The aim of our experiment related to the development of the fertilisation consultancy system of winter barley was to examine the effect of N, P and K supply on the yield, protein content, amino-acid composition and element content of winter barley in the case of distinctive nutrient supply levels in a long-term fertilisation experiment, as well as to determine the N, P and K supply limit values for chernozem meadow soil. The long-term fertilisation experiment was established in 1989 on deeply carbonated chernozem meadow soil on 4–4 N, P and K supply levels in a whole treatment combination with 64 treatments and split-split-plot design. Of the results of the experiment performed in 2006 and 2007, this study focuses on the effect of N and P supply level on the amino-acid composition. The main conclusions are summarised below.

1. The increasing N supply of the high N providing capacity soil containing 2.8–3.2% humus gradually and significantly increased the raw protein content until 13.9%. The increase of raw protein content was followed by the significant increase of the amount of all 17 examined amino-acids calculated for g per 100 g dry matter. There was a significant change of amino-acid quantity until the 160 kg N ha-1 fertilisation level. Higher N supply levels (240 kg N ha-1) resulted in further significant increase only in the case of certain amino-acids.

2. In the majority of the examined cases, N fertilisation resulted in a negative change in the amino-acid composition of raw protein (g per 100 g raw protein). Especially as a result of overfertilisation (240 kg N ha-1), when the share of lysine and threonine of essential amino-acids and asparagine, cystine, glycine, proline and serine of nonessential amino-acids decreased within the raw protein.

3. At the proper P supply level, if the AL-P2O55 content of the soil was between 185–225 mg kg-1, the raw protein amino-acid composition of winter barley did not significantly change in comparison with the treatment with no P fertilisation (140–150 mg kg-1 AL-P2O55). Changes and, more often, negative effects were observed in the amino-acid composition of the raw protein only at higher P supply levels (270–285 mg kg-1 AL-P2O5).

Keywords: winter barley, N and P supply, amino-acid composition, long-term experiment