In the spring of 2017 we established grassland experiment to study changes in grass productivity and composition due to use of mineral fertilizers on preceding sheep winter camp. The experiment comprised of two locations, namely south winter camp and north winter camp. The studied treatment was mineral fertilization with four levels: control, PK fertilization, NPK fertilization and N fertilization. The experiment showed that the various fertilization methods affected the amount of herbage yield and the botanical composition of the grass. The experiment showed that the different fertilizers affected the yield and the botanical composition of the grass sward. The average annual yield was expected to be the highest in fertilization with NPK (8,97 t DM/ha), followed by fertilization with N (8,46 t DM/ha), then fertilization with PK (7,37 t DM/ha) and control reached 7,23 t DM/ha. At first cut no diferences were obtained between functional groups. At the second cut fertilizing with PK increased the average proportion of legumes, the average proportion of grasses decreased and the average percentage of the herbs remained the same as in the control. Fertilization with NPK increased the average proportion of grasses and reduced the average proportion of herbs. Fertilization with N reduced the average proportion of legumes and herbs and increased the average proportion of grasses twice according to control. The third cut when compared to control and fertilization with PK did not show any effect, fertilization with NPK increased the average proportion of grasses and decreased the proportion of herbs and legumes. Fertilization with N affected the same as at the second cut. The results showed that some of the variables studied in the experiment responded already during the first year of the experiment and some require a much longer duration of modified grassland management.