Field experiments over 2001–2003 examined the effectiveness of magnesium-andmicroelements fertilizers in winter wheat, corn, winter rape and sugar beet depending on the date and rate of foliar application. The yield, productive effectiveness of 1 kg of Sonata fertilizer and economic effectiveness were defined for two dates, at the dose of 2, 4 and 6 kg ha-1. Foliar application of fertilizers of winter wheat took place at full tillering and the beginning of earing; corn at 6–8 leaf stage and the plant height of 50–60 cm, winter rape – at the beginning of inflorescence branch formation and the green-dense-bud stage, while sugar beet – 6–8 leaf stage and row closing. Foliar application of magnesium-and-microelements fertilizers, Sonata increased the winter wheat yield mean in research years by 100–250 kg of grain, corn yield by 50–290 kg of grain, winter rape by 110–260 kg of seeds and sugar beet by 100–1500 kg of roots per hectare. The greatest effectiveness of foliar application of fertilizers expressed as the yield increase value per 1 kg of the fertilizer applied and the value of yield increase per Polish zloty 1 of the cost of fertilizer in winter wheat cultivation occurred at the rate of 2 kg ha-1 applied at full tillering and in corn at the dose of 4 kg ha-1 at plant height of 50–60 cm. The most effective method of winter rape fertilization was the application of 2 kg of Sonata per ha at the green-dense-bud stage and sugar beet with 4 kg ha-1 at row closing.