The effects of different N, P and K supply levels and their combinations were examined on the hay yield and mineral element content of an established 2 year old all-grass sward in the 29th year of a long-term fertilization field experiment set up on a calcareous chernozem soil. The soil of the growing site contained around 3% humus, 3-5% CaCO3, 20-22% clay in the ploughed layer and was originally moderately well supplied with available N, K, Mg, Mn and Cu and poorly supplied with P and Zn. The trial included 4N×4P×4K=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 and the area was prone to drought. In 2002, the area had 401 mm precipitation and gave 2 cuts of grass. The 1st year results of the trial were published earlier (Kádár, 2005a, b). The main conclusions can be summarised as follows:
1. As a function of N×P fertilization the two cuts of the hay yield made up 1.4-8.0 t/ha while the green herbage 5.0-24.0 t/ha. The N-fertilization was of vital importance, which increased the hay mass 5 times. The P-response was moderate in the 1st, cut while there were no K-responses at all on this soil with 135 mg/kg ammoniumlactate (AL) soluble K2O values in plough layer.
2. On those plots well supplied with PK the 100 kg/ha/yr N-treatment gave a total of 48 kg surplus hay/kg N applied. The 200 kg/ha/yr N-treatment yielded 11 kg, while the 300 kg/ha/yr N-treatment yielded 4 kg surplus hay/kg N applied. The NO3-N content of the 1st cut hay increased over permitted 0.25% level when using the maximum N-rate and made up this NO3-N form 26% of the total-N pool. The optimum PK-supplies in this site seems to be about 130-150 mg/kg AL-P2O5 and AL-K2O in plow layer with 200 kg/ha/yr N applied.
3. N-fertilization enhanced the content of N, K, Mg, Na, Mn, Cu and NO3-N, while the concentration of S, P, Al, Fe, B and Mo dropped in the primary hay. The increasing P-supply stimulated the uptake of P, Ca, Mn, Sr and Ba, while hinderned the uptake of S and Mo. The K-fertilization rose the content of K and Ba and diminished the concentration of Mo and the antagonistic metal cations like Ca, Mg and Na.
4. The NPK fertilization-induced Mo-deficiency can first of all jeopardized the fodder quality in this site. On the unfertilized plots the hay showed around 1.0 mg Mo /kg D.M., while on the N3P3K3 plots 0.1-0.2 mg/kg D.M. The P/Mo ratio lifted from 2-4 thousand up to 20 thousand. In the 2nd cut this phenomena partly disappeared, while developed the P-Zn antagonism. On P-control plots measured 15 mg/kg Zn
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dropped to 10 mg/kg while the P/Zn ratio rose from 167 up to 364.
5. The 2nd cut hay had a little yield, yet was rich in minerals having 30-50% higher average element content compared with the primary hay. However the N, Al, Fe and Mo showed 2-times higher concentrations in the 2nd cut hay. There were found extra large, 25-fold differences in hay Na content as a function of N×K supply levels under synergetic effect of N and antagonistic effect of K treatment.
6. Summarizing the above we can state that the long-term fertilization may drastically change the content and ratios of elements built in hay through synergetic or antagonistic effects. In the air-dried 1st cut hay for example, the minima-maxima concentrations of measured elements varied as follows: N 0.7-3.0%, K 1.3-3.0%, Ca 0.3-0.5%, Mg 0.13-0.21%, S 0.15-0.32%, P 0.10-0.32%; Na 50-1400, Mn 60-120, Al 50-120, Fe 70-140, Sr 8-170, Zn 6-40, Ba and B 3-6, Cu 2.5-5.5, Ni 0.4-1.4, Mo 0.1-1.0 mg/kg.