The effect of different N, P and K supply levels and their combinations on the yield, mineral composition, grain amino acid content and disease resistance of maize (Mv 380) and on the available PK content and cellulose-decomposing activity of the soil was studied on calcarcous, loamy chernozem soil in the experimental nursery of the Research Institute for Soil Science and Agricultural Chemistry of the Hungarian Academy of Sciences. The soil contained 5% CaCO3, 3% humus, poor P and Zn supplies, moderate N and K supplies and satisfactory Mn and Cu supplies, with a PH(KCl) of 7.3. The mineral fertilisers were applied in the form of 25% calcium ammonium nitrate, 18% superphosphate and 50% potassium chloride. The fore-crop of the maize was wheat for two years, prior to which alfalfa was grown on the area for four years. The main conclusions were as follows: 1. On average approximately half the fertiliser P and one-fifth of the fertiliser K introduced into the soil could be detected in ammonium lactate-soluble form. Some 20-25% of the superphosphate P could be demonstrated in the NaHCO3-soluble P fraction obtained from the ploughed layer in the third year of the experiment. 2. The yield was regulated by the PxK supplies; N effects were not observed as it was a very dry year. As the result of excessive P there was a significant reduction in the plant density, 1000-kernel mass and kernel yield at harvest. One-sided fertilisation with P led to a kernel yield of 3.4 t/ha, while balanced P and K supplies resulted in 6.2 Vha. 3. Excess N led not to an increase in yield, but to a rise in the incidence of common smut (Ustilago maydis). This was partially counterbalanced by an improvement in the P supplies. Fusarium stalk rot infected the whole crop after excessive P application; this could be moderated in part by improving the K supplies. 4. The mineral composition of maize shoots in the 6-leaf stage gave a good reflection of the nutrient supplies in the soil. As suggested in the literature, plant analysis at this stage of development could be useful for diagnostic purposes and as the basis of fertilisation recommendations. As the P supplies increased, the P/Zn ratio rose to above 200, indicating the onset of Zn deficiency. 5. The greatest modifications in the mineral composition of the grain and stalk at harvest were also caused by P fertilisation. The P/Zn ratio of the grain increased 2.5 times and rose to above 200, while the stalk P/Zn ratio exhibited a 15-times increase, from 22 on the control soil to 330. On this plot a violent storm prior to harvest caused the whole stand to lodge. 6. The amino acid composition of the grain yield remained relatively constant since the N effects were negligible. A moderate increase in the P supplies caused a slight increase in the quantity of essential amino acids. 7. The cellulose-decomposing activity was significantly reduced in the 1st and 2nd years by the application of a large quantity of KCl to the wheat forecrop; this reduction was moderated or eliminated by an improvement in the P supplies. Positive NxP interactions were dominant in the third year, under maize. The 3-month exposure time under wheat led to 52-55% decomposition, while the 4-month exposure under maize resulted in only 26% decomposition, since the soil dried out and the two wheat years produced unfavourable, poor quality organic matter with a wide C/N ratio. 8. PxK interactions were generally dominant in the nutrient uptake. The uptake of P, Zn and Mn was determined chiefly by the P supplies. At harvest the quantity of P and Mn incorporated into the aboveground yield was 71% greater than in the control, while the Zn uptake dropped to 45% on plots overfertilised with P. The clement requirements of maize for 1 t grain + the corresponding stalks were as follows: 22 kg N, 12 kg K2O, 11 kg P2O5, 4 kg Ca, 2 kg Mg, 390 g Fe, 76 g Mn, 36 g Zn and 11 g Cu. 9. On this soil increasing the ammonium lactate-soluble P2O5 content to more than 120-180 mg/kg or the K2O content to above 200-250 mg/kg will not improve either the yield, the mineral and amino acid compositions, or the cellulose-decomposing activity of the soil.
