One of the aims of our experimental work to develop the soybean fertilization consultancy system was to develop reliable nutrient limit values for the use of plant analysis for diagnosticpurposes based on the results oflong-term fertilization experiments. The long-term fertilization experiment was established in 1989 on chernozem meadow soil with deep calcareous layers at four different N-, P-, and K-supply levels, respectively, in a complete treatment combination with 64 treatments. During the 11-year soybean fertilization experimental cycle, we performed plant diagnostic tests between 2003 and 2007, the main results of which can be summarized as follows.

Increasing doses of N fertilization resulted in higher N concentration of soybean leaf in the initial phase of soybean flowering (R1-R2). On soils with good P, K and Mg supply, N supply did not affect the P, K and Mg content of the leaf for most of the years. There was a strong positive correlation between leaf N and Mn concentrations, while there was a strong and very strong negative correlation between N and Zn and N and Cu, respectively. On soils with adequate P-supply, only excessive P-supply induced higher leaf Pconcentrations. Antagonism of P-Zn and P-Cu has been detectable for most of the examined years, primarily at very good or excessive levels of P-supply.

The K content of soybean leaf increased reliably up to the soil ALK2O supply level of 350 mg kg-1. Based on leaf diagnostics, K-Ca and K-Mg antagonism showed only in the case of very good, excessive K-supply in one of the years. In addition, a very good, excessive K supply sometimes caused a significant decrease in the Zn and Cu content of the leaf.

The nutrient limit values characterizing the satisfactory nutritional status of soybeans in the initial phase of flowering, based on leaf analysis are as follows: N 2.8–4.5%, P 0.35–0.50%, K 1.7–3.0%, Ca 1.2–2.0%, Mg 0.3–0.7%, S 0.2–0.4%, Fe 100–200 mg kg-1, Mn 60–130 mg kg-1, Zn 25–60 mg kg-1, Cu 4–12 mg kg-1, B 20–60 mg kg-1 and Mo 1.0–5.5 mg kg-1.

Keywords: soybean, plan analysis, nutrient content, long-term experimen