Yield elements (plant height, grass yield) of prairie grass, the little known grass species in Hungary, was investigated in a three-factor field experiment set up on the Mohács-island. One-grass and grass/legume mixture were established under irrigated and non-irrigated conditions at different nitrogen levels (0-67-133 kg N/ha/year). The effects of these factors on the grass productivity were analysed by a three-factor analysis of variance at 5% significance level in the first year of the experiment. Nitrogen supplementation and the interaction of legumeXirrigation had a significant positive effect on the annual hay yield. The yield of the first two cuts, which accounted for 61% of the annual yield, was not significantly affected by any of the examined factors, while their effect was already clearly visible in the yield of the 3rd and 4th cuts. A similar result was obtained with the model fitted to the average height of the four cuts, but the legumeXirrigation and legumeXnitrogen interactions were already significant in the 2nd cut. Nitrogen had a positive effect on grass height from the 3rd cut. Without irrigation, the 1st cut showed a significantly lower grass height with legume addition. In our experiment, we estimated 65 t/ha annual fresh grass yield on average of the treatments, and 18 t/ha of hay was actually harvested. In the treatment of irrigation with legume addition, 1 kg/ha of excess nitrogen resulted in an excess of 150 kg/ha of fresh grass yield in the case of the higher dose nitrogen treatment, compared to the nitrogen control. The laboratory analysis of the 1st cut-hay samples from selected treatments confirmed favorable protein (16.7-18.2%) and crude fat content, its lower crude fiber content and higher calcium and phosphorus content compared to cocksfoot and smooth brome.