The effects of different N, P and K supply levels and their combinations on the development, yield and N-uptake of an established all-grass sward were examined in the 28th year of a long-term fertilization experiment set up on a calcareous chernozem soil. The soil of the growing site contained around 3% humus, 5% CaCO3, 20-22% clay in the ploughed layer and was originally moderately well supplied with available K, Mg, Mn and Cu and poorly supplied with P and Zn. The trial included 4Nx4Px4K=64 treatments in 2 replications, giving a total of 128 plots. The fertilizers applied were Ca-ammonium nitrate, super phosphate and potassium chloride. The groundwater table was at a depth of 13-15 m and the area was prone to drought. In 2001, however, the area had a satisfactory amount of 621 mm precipitation with a fairly good distribution. The grass was established on 21. September 2000. The main results and conclusions can be summarised as follows:
     1. Grass herbage had a very favourable wet year in 2001 with over 700 mm rainfall during the total vegetation period. The hay yield of unfertilised control plots was by the 1st cut 1.7 t/ha, by the 2nd cut 1.2 t/ha, while the N3P3K3 treatment gave 8.8 t/ha and 4.2 t/ha resp., so NPK fertilization increased the air-dried hay yield from 3 t/ha to 13 t/ha (1st+2nd cuts together).
     2. The N-requirement of the young grass was moderate while the P-response significant by the 1st cut. The optimum P-supply was at the 150 mg/kg ammonium lactate soluble AL-P2O5 in the plow layer. There were no K-responses on this soil with 135 mg/kg AL-K2O values.
     3. There were no P responses any more by the 2nd cut even on the low P-supply soil, with 66 mg/kg AL-P2O5 value, while the applied N increased the hay yield 4 times. The optimum N content in the hay, leading to maximum yield, amounted 2% by the 1st cut and 2.5-3.0% at the 2nd cut. Applied N decreased air-dried content at the 1st cut from 33% to 31%, at the 2nd cut from 27% to 21%.
     4. On the soil, well supplied with PK, the 100 kg/ha/yr N treatment gave the maximum hay surpluses: at the 1st cut 61 kg, at the 2nd cut 14 kg, that is a total of 75 kg hay/kg N applied. The 200 kg/ha/yr plots yielded 43 kg, 300 kg/ha/yr yielded 34 kg hay/kg N applied. The primary sward hay had 0.34% NO3-N in the 300 kg/ha/yr treatment, which was over the allowable 1.25% NO3-N limit for animal foodstuff. The NO3-N content in the N-control plots amounted 0.06%, in the 100 kg/ha/yr treatment 0.10%, in the 200 kg/ha/yr treatment 0.22%. At the 2nd cut the hay had generally, half as high NO3-N content as in the 1st cut hay in all treatments.
     5. The apparent recovery of applied N, using difference method, was even more than 100% on the well supplied with PK soil suggesting that in these instances grass herbage could make a good use of soil NO3-N pool accumulated in soil during the previous period and not used by the crops.