Foliar application of fertilizers containing biostimulators can influence yield and the uptake and accumulation of NO₃^- by plants. The aim of the research was to determine the influence of foliar nutrition with ‘Pentakeep V’ and diverse doses of nitrogen fertilization on yield, plant nitrogen metabolism and nutritional quality of spinach. The experiment design included two sub-blocks with and without foliar nutrition. Plants with foliar nutrition were sprayed twice with 0.02% w/v ‘Pentakeep V’ fertilizer (3000 dm³ water per 1 ha). In each sub-block soil nitrogen fertilization (in the form of ammonium nitrate) was applied in following combinations: 1 – control (without N), 2 – 50% N dose prior to seed sowing (25 mg N∙dm^-3 of soil), 3 – 100% N dose prior to seed sowing (50 mg N∙dm^-3 of soil). The interaction between foliar nutrition and nitrogen fertilization had a significant effect on the content of: nitrates(V), soluble oxalates and ascorbic acid in spinach leaves. The effect of tested factors on the content of nitrates(V) and ascorbic acid was additionally modified by the weather conditions in both years of research. Foliar application of ‘Pentakeep V’ resulted in decreased concentration of soluble oxalates in control plants (without N) as well as higher amount of these compounds in plants fertilized with 100% of N dose. No significant effect of tested interaction was observed in the case of yield and the content of: dry matter, nitrates(III), ammonium ions, free amino acids, N-total, soluble sugars and phenolic compounds in spinach leaves.

25-36