The interactions between N×Cu×Mo were examined in potato in a field trial on calcareous chernozem loamy soil in 1993. The ploughed layer of the soil at the production site contained 3% humus, 5% CaCO3 and 20% clay. Based on the performed soil analyses, the area contained proper amounts of Ca, Mg, K, Mn, satisfactory amount of Cu and weak-average P and Zn. The groundwater level was 13–15 m and the area is drought sensitive. The experiment was established with 4N×3Cu=12 treatments×3 replications=36 plots and a split-plot design. N fertilisation was applied in doses of 0, 100, 200, 300 kg ha-1, while Cu was applied in doses of 0, 50, 100 kg ha-1 in the form of Ca ammonium nitrate and CuSO4. In the 5th year of the experiment, the 15 m long plots were divided in half and separated from each other with 1m wide paths. The experiment became a striped split-plot trial with 4N×3Cu×2Mo=24 treatments×3 replications=72 plots. The 48 kg ha-1 Mo was applied in the form of (NH4)6Mo7O24∙4H2O. Main conclusions:

The total amount of rainfall was only 140 mm during the 150-day-long growing season of potato. N fertilisation caused depression. The 16 t ha-1 potato tuber yield of the N control was 9.8 t ha-1 in the case of 300 kg ha-1 year-1 N. Cu and Mo doses did not affect yield.

As a result of the abundant N fertilisation, the concentration of N, Mg, Na, Fe and Zn increased in the leaf, while the uptake of S, B and Ba was blocked. As a result of CuSO4 applied six years ago, the Cu content doubled in the yield, while it increased by 20–25% in the tuber yield. Mo fertilisation increased the Mo stock of leaves by two magnitudes, and that of the tubers by one magnitude (10–20 times as high).

As a result of NO3-molybdenate antagonism, the Mo content of leaves decreased nearly to half, while the Mo content of the tubers decreased by one third on soils contaminated with Mo. Also, Mo concentration decreases with the age of leaves. The tuber yield was prevented from the hyperaccumulation of Mo to a certain extent.

As a result of CuSO4 applied six years ago, the Cu content doubled in the yield. The Cu content of the tubers also increased moderately. In the case of similar production circumstances, the element need of the 10 t ha-1 tuber yield equals to 18 kg N, 25 kg K2O, 8 kg P2O5, 1 kg CaO and 1–2 k MgO. Our data can be used in the calculation of the element need of the planned potato yield for consultancy purposes.

Keywords: N×Cu×Mo treatment, field trial, potato, calcareous chernozem soil