Effect of fertilization on the content of macronutrients in fruits of milk thistle (Silybum marianum L. Gaertn.)

Milk thistle was grown on a substrate with the texture of light soil, slightly acid in reaction and moderately abundant in available phosphorus, potassium and nitrogen. The effect of incremental nitrogen fertilization (0.0, 1.0, 2.0, 3.0 g N per pot) against the background of constant PK fertilization (P – 1.0, K – 1.5 g per pot) on the content of macronutrients in fruits of two forms of milk thistle, a cultivar called Silma and a population line bred in Poland, was tested in the first trial; the influence of boron fertilization was assessed in the second series and the impact of forms of magnesium fertilizers (MgCl2 and MgSO4) was analyzed in the third variant of the experiment. The variety-specific traits had a significant effect on the content of nitrogen, phosphorus and potassium, but did not affect the concentrations of calcium, magnesium and sodium. The content of nitrogen in achenes of the population plant was 26.38 g N kg–1 d.m., compared to 25.16 g N kg–1 d.m. determined for cv. Silma. Fruits of the population line also contained significantly more phosphorus and potassium (by app. 17%), whereas the levels of sodium, calcium and magnesium did not differ in a statistically significant way between the two types of the plant. The highest nitrogen (27.62 g kg–1 d.m.) and phosphorus (8.78 g kg–1 d.m.) concentrations were obtained by applying 2 g N per pot. Sulphur introduced to soil in the form of magnesium sulphate raised the content of nitrogen in achenes of both forms of milk thistle.