The effect of the P supply of soil on the grain yield of maize, its level of P and Cu supply and the interaction of these two nutrients were examined in a long-term maize fertilisation experiment.

The long-term fertilisation experiment was established in 1989 on chernozem meadow soil with deep calcareous layer, the N, P and K levels of supply were 4 each in a total treatment combination with 64 treatments. Main soil characteristics: humus layer thickness: 85-100 cm, humus content: 2.8-3.2%, pH(KCl) of the cultivated layer: 5.0–5.2, plasticity (KA): 50, clay content: 32%, AL-P2O5 content depending on P fertilisation: 120–360 mg kg-1, EDTA Cu content: 5.4 mg kg-1.

In this study, the P fertilisation results of the 12th-19th years of the long-term experiment (between 2001 and 2008) are presented. Based on these results, the following conclusions can be drawn:

Averaged over the eight years, maize grain yield was 7.39 t ha-1 on the acidic clayey adobe soil whose level of P supply was between 120–150 mg kg-1 AL-P2O5 without P fertilisation. The highest grain yield was obtained at the 160–220 mg kg-1 AL-P2O5 supply level. No significant yield change could be shown in the case of higher levels of P supply (up to 360 mg kg-1 AL-P2O5 value).

According to the results of the leaf analysis performed at the beginning of tasseling, more favourable levels of P supply were accompanied by higher P concentrations of the maize leaf. The satisfactory P supply level limit value determined on the basis of the correlation analyses between the P concentration of the maize leaf and grain yield was observed at the 10-14 t ha-1 yield level and the 0.20–0.37% P concentration.

In our formulas, the satisfactory Cu concentration at the 10-14 t ha-1 yield level is 2–11 mg kg-1 Cu. Based on the performed experiments, the lower limit of Cu nutrition (2-5 mg kg-1 Cu) at high yield levels is lower than those published in the specialised literature.

The P-Cu antagonism which accompanies the increasing level of P supply could be relatively frequently observed from the 190 mg kg-1 AL-P2O5 supply level of the soil, but no yield reduction was triggered by the moderate Cu incorporation in the 160–360 mg kg-1 AL-P2O5 supply interval at the favourable Cu supply level.

The satisfactory P/Cu ratio at the beginning of tasseling was between 250-550 at the 10–14 t ha-1 yield level in seven of eight years which conforms to the values published in international specialised literature. However, our experimental results showed that high yields can also be obtained at the 900–1100 P/Cu ratio.

Keywords: P fertilisation, P and Cu nutrition level, P-Cu interaction, maize, long-term experiment