The field experiment with mixtures of barley, husked oat and naked oat with field pea was conducted in 2005-2007 at the Podlasie Centre for Agricultural Consultancy in Szepietów (53^o7’ N; 22^o9’ E). One experiment was established on the soil of the good wheat complex (soil pH above 5.5; in the stand after wheat), and the other on the soil of the good rye complex (soil pH 4.8-5.5; in the stand after triticale). The effect of nitrogen rates: 0, 25 and 50 kg·ha^-1 on seed yield, total protein content in seeds of both mixture components, protein yield and mass fraction of the components in seed and protein yield were studied. Barley was more suitable for cultivation in mixture with pea than oat (especially in better soil conditions), due to higher yields of seeds, protein and net energy. For mixtures of barley and oat with pea the rate of N – 25 kg·ha^-1 turned out to be sufficient. Percentage of pea in seed yield of mixtures with cereals was small (16-32%), and in protein yield – 24-41%. Higher percentage of protein deriving from pea was found in the mixture with naked oat than in mixtures with husked cereals.

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