P—Zn kölcsönhatás mészlepedékes csernozjom talajon kukorica monokultúrában | P—Zn interactions in a maize monoculture on calcareous chernozem

A long-term field P—Zn fertilization experiment was set up in autumn 1978 on calcareous chernozem soil with a deep humus layer and loam texture, formed on loess, at the Nagyhörcsök Experimental Station of RISSAC. The ploughed layer contained 5% CaCO ₃ and 3% humus, and was satisfactorily supplied with Ca, Mg, Mn and Cu, moderately well with N and K, and poorly with P and Zn. The groundwater depth was 13–15 m and the area was prone to drought, with a negative water balance. The experiment was set up with 4P × 3Zn = 12 treatments in 3 replications, using a split-plot design. The plot size was 4.9×15=73.5 m². 0, 100 kg/ha/year, 500 kg/ha/5 years, 1000 kg/ha/5 years P ₂O ₅ fertilization were applied to the main plots, while subplots were given 0, 20, 40 kg/ha/5 years Zn fertilization in the form of superphosphate and ZnSO ₄. The whole experiment received 200 kg/ha N and 200 kg/ha K ₂O fertilizer as basic fertilization in the form of NH ₄NO ₃ and KCl. The maize hybrid grown was Mv SC 580. The following conclusions can be drawn from the results of the first 4 years: Under the given experimental conditions, where the soil was poorly supplied with P, the 100 kg/ha P ₂O ₅ fertilization applied was sufficient to satisfy the P requirements of maize. This quantity of P could also be given in a single dose in advance for 4–5 years. Replenishment with 1000 kg/ha P ₂O ₅ was uneconomical and led to yield losses due to the induced Zn deficiency. The optimum ammonium-lactate (AL)-soluble P ₂O ₅ content was indicated by a value of 100–150 mg/kg in the ploughed layer. The overdominance of P and the grain yield losses caused by 1000 kg/ha P2O5 could be counterbalanced by 40 kg/ha Zn fertilization. The optimum Zn content determined using the KCl+EDTA method was indicated by a concentration of 2–3 mg/kg in the soil. In agreement with doses recommended in the literature, balanced maize nutrient status was indicated by 0.3–0.5% P and 30–60 mg/kg Zn in the air-dry shoot in the 4–6-leaf stage, while the optimum composition in the leaf at tasselling was 0.25–0.40% P and >25 mg/kg Zn concentration. The ideal value of the P/Zn ratio in the vegetative plant organs was estimated as 50–150. If this P/Zn ratio rises much over 200, the need for Zn fertilization is indicated. P excess increased the incidence of barren plants in 1978, when there was a drought during grain filling in August. In this year 13–20% of the plants were barren.