The effects of different N, P and K supply levels and their combinations were examined on the mineral element content of an established all-grass sward with seed mixture of eight grass species in the 28th year of a long term fertilization field experiment set up on a calcareous chernozem loamy soil. The lay-out and method of the trial as well as the fertilizer responses on the hay yield were published elsewhere (Kádár 2004). The effect of fertilization on the nutritional values and nutrient yield also described earlier (Kádár and Győri, 2005). 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, superphosphate and potassium chloride. The groundwater table was at a depth of 13-15 m, the area was prone to drought. In 2001, however the area had a satisfactory amount of 621mm 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. As a function of N-fertilization the element content of the 1st cut hay usually increased, except for Al and Mo, which showed dilution effects. The concentration of K, Ca, Mg, Mn, P, Sr, B, Ni enhanced with 25-50%, S and Co with 60-70%, N and Cu 2-times, NO3-N and Na about 5-times compared to the N-control. The P-fertilization stimulated uptake of Mn and Mg for 10-20%; S, NO3-N and Co for 40-50%, Na and for Sr 60-70%, P for 90%, however, inhibited the uptake of Zn and Co for 20-40%, Al and Fe for 50-60%, Mo for 70% compared to the P-control.
     2. The P/Zn ratio showed on P-control soil optimal values of 118, while on highly P-supplied soil 278 P/Zn ratio, so indicating Zn-deficiency. As a function of PxK negative interactions, concentration of Fe dropped from 307 to 105 Al from 206 to 60, Mo from 0.44 to 0.05, Cr from 0.33 to 0.12 mg/kg in air-dry hay. The Cu/Mo ration on N-control soil showed the optimal value of approx. 10, while on heavily fertilized with N soil that of 40-80, indicating extreme Mo-deficiency.
     3. The 2nd cut hay contained about 20% more N, K, Ca, Mg, Na, 40% more Cu, 70-80% more S and Mn, 90% more Fe and P, 140% more Al and nearly 5-times more Mo. The content of B did not changed, while NO3-N dropped about 40% . The Cu/Mo ratio showed value of 2.6 on N-control soil, while on heavily fertilized with N soil ratio of 7.8. The P/Zn ratio indicated on P-control soil optimal value of 150, while on overfertilized with P soil value of 269. So, the P-induced Zn-deficiency could also be proven in the 2nd cut hay, while the Cu-induced Mo-deficiency disappered.
     4. The N-fertilization stimulated in the 2nd cut hay also the accumulation of elements N, K, Mg, P, Mn, Cu and Ni with 20-50% compared to the N-control. The NO3-N increased 4-times, while Na content 10-times. However the elements Fe, Al, B, Mo and Cr showed a dilution effect with 20-60%. The P-fertilization increased the concentration of Mn, Sr, Cd, Co, S and P, while decreased the content of Na, NO3-N, Cu and Zn. As a general rule, the K-fertilization hindered the accumulation of metal cations. The P-induced Cd accumulation was fully counterbalanced by increasing K-supply of soil.
     5. Summarizing above we can state that the long-term fertilization can drastically (in some cases with an order of magnitude) change the concentrations and ratios of elements built in hay through synergetic or antagonistic effects. In the 1st cut hay, for example, the minima-maxima contents of measured elements varied in air-dry hay as follows: N 0.90-3.02, Ca 0.4-0.7, S 0.14-0.32, P 0.12-0.30, Mg 0.10-0.24%; Na 70-700, Fe 100-288, Al 45-250, Mn 71-130, Sr 10-22, Zn 7-14, Ba 6-11, B 3.6-8.1, Ni 0.3-1.6, Cr 0.1-0.4, Mo 0.04-0.44, Co 0.04-0.12 mg/kg.