The aim of the research was to evaluate the influence of diversified mineral fertilization (N,P,K) on the content of some nitrogen forms (total nitrogen, protein nitrogen, N-NH4, N-NO3) in orchard grass ( aboveground parts and roost). The study presented has been based on the results of a field experiment which lasted three years and was localized and carried out on Haplic luvisol (acc. to FAO) developed from loess. The field experiment included 27 fertilization objects – against the background of three increasing phosphorus fertilization levels nine nitrogen-phosphorus combinations were applied after random selection. The whole dose of phosphorus and half a dose of potassium were sown before orchard grass sowing and in the second and third year after the third hay harvest cut. Nitrogen was sown in the early spring and after the first and second hay harvest cuts in three equal parts. Fertilization with nitrogen and phosphorus influenced significantly the content of total nitrogen and protein nitrogen in aboveground parts and in roots of orchard grass. The content of N-NH4 and N-NO3 depended considerably on nitrogen fertilization (N-NO3 in roots – also on potassium fertilization). The content of evaluated forms of nitrogen in orchard grass depended significantly and positively mostly on the content of N-NH4 and N-NO3 in the soil. Uptake of this component was significantly and positively dependent on the content of N-NO3 in the soil.