The aim of this study was to determine the effect of a catch crop on the content of nutrients in grain of spring barley grown after it, intended for animal feed, using different intensities of chemical plant protection and nitrogen fertilization. Field experiments were carried out at the Research Station at Mochełek on Alfisols, in 2008-2011. The split-plot experimental design was used. The effect of the catch crop (field pea plowed in autumn of the year preceding the barley sowing – factor I) on N, P, K, Ca, Mg and crude fiber content in grains of barley grown with the use of different levels of chemical plant protection (low and high – factor II) was evaluated. Moreover, different rates of nitrogen fertilization were tested (0, 35, 70, 105 and 140 kg·ha^-1 – factor III). The catch crop plowed in the autumn as a green manure significantly increased the nitrogen and phosphorus content in spring barley grain. Intensity of chemical protection of barley had no effect on the content of N, P, K, Ca, Mg and crude fiber in the grain. Increasing the rate of nitrogen in the range from 0 to 140 kg·ha^-1 contributed to increase in concentrations of N, P and K in grain and reduction in the content of Mg. The content of P, K, Ca and crude fiber was negatively correlated with the yield of pea biomass plowed in. Ca concentration in the grain was also negatively correlated with grain yield, whereas magnesium content was positively correlated with both the yield of pea biomass plowed in and grain yield of barley. The study confirmed the importance of the catch crop used as green manure in improving the quality of spring barley grain. Research hypothesis has not been fully confirmed in the impact of this factor on the grain composition of barley grown under low nitrogen fertilization. In treatments without N fertilization the catch crop used as green manure had only an effect on the Ca content in the grain. Barley fertilized with nitrogen at 35 kg·ha^-1 responded significantly to the catch crop used as green manure only by increasing the concentration of potassium and magnesium in the grain.

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