A repce (Brassica napus L.) tápláltsági állapotának megítélése növényanalízissel | Estimation of the nutrient status of rape (Brassica napus L.) by means of plant analysis

The effect of different N, P and K levels and their combinations on the element composition and major nutrient ratios of rape (variety Yet Neuf) was investigated in the 11 ᵗʰ year of a long-term fertilization experiment set up on calcareous chernozem soil. Correlations were also sought between the NO ₃-N reserves of the 0–60 cm soil layer and the N% of the rosette-stage shoot, the total plant N% and the seed yield/oil %. The diagnostic limit values used to estimate the nutrient status of rape were checked and new recommendations were elaborated for the extension service. The ploughed layer of the experimental soil contained 3% humus, 5% CaCO ₃ and 20% clay, and was poorly supplied with P and Zn but moderately well supplied with N and K. The experiment included 4N×4P×4K = 64 treatments in 2 replications, giving a total of 128 plots. Fertilizers were applied in the form of 25% calcium ammonium nitrate, superphosphate and potassium chloride. The groundwater was located at 13–15 m depth and the area was drought-sensitive. The major results were as follows: Satisfactory N supplies are indicated by a 4–5% N content in the rosette-stage shoot or in fully developed leaves at the beginning of flowering, in agreement with the optimum values given in the literature. With an improvement in the N supplies there was also an increase in the cation content (Ca, Mg, Na) of the plant organs. The NO ₃-N content of the rosette-stage shoot changes by an order of magnitude as a function of the supplies and is excellently suited for diagnostic purposes. The optimum range of N supplies is indicated by 5–10 mg/g (i.e. an NO ₃-N concentration of 5–10 ‰ in the dry matter). The ratio of NO ₃-N in plant N content increased from 4 to 20% with extreme N supply as compared to the control. Satisfactory P supplies for rape are reflected by 0.6–0.7% P contents in the rosette-stage shoot or 0.4–0.5% in the leaves at flowering. Improved P supplies led to a significant increase in the Na concentration and a reduction in the Zn and Cu concentrations in the plant organs. The P-Zn antagonism may lead to latent Zn deficiency on soils with good P supplies, according to the limit values in the literature. Some of the nutrient ratios fluctuated between wide limits, providing a sensitive reflection of the balanced nature and quality of plant nutrition. This could serve to make the extension service recommendations more reliable. In the case of N/P, which is the most important ratio, a value of 8–10 in the rosette-stage shoot or 10–12 in the leaves at flowering could be a satisfactory guideline. In agreement with data in the literature, values ranging from 50–150 could be optimum for the P/Zn ratio, both in the rosettestage shoot and in the leaves at flowering. A common optimum cannot be given for the P/Cu ratio, since in the leaves at flowering this ratio is reduced to approximately a third of that measured in the rosette-stage shoot. Guidelines could be 500–1500 in the leaves and 2000–3000 in the shoot, but the present experiments were not suitable for the accurate determination of the optimum P/Cu ratio. The optimum N/K ratio for balanced N and K supplies can be estimated as 0.8–1.2 in the rosette-stage shoot and 1.2–1.6 in the leaves at flowering. The optimum K/P ratio was around 6–8 in all the aboveground vegetative plant organs. In spring the tested soil needed to have NO ₃-N reserves amounting to 100–150 kg/ha if the rosette-stage shoot was to have a N content of around 5%, to ensure maximum seed yields. A linear negative correlation was found between the N% of rosettestage shoot and the oil content of the seed yield. An excess of N enhances the protein content at the expense of the oil yield. Early plant analysis can be used to predict quality. On this soil the optimum PK supply for rape is 150–200 mg/kg AL-soluble P ₂O ₅ or K ₂O in the ploughed layer. Sufficient N supply is around 100 kg/ha N, or 100–150 NO ₃-N reserve in the 0–60 cm soil layer before sowing or in spring. These data may serve as guides for Hungarian extension service.