The study aimed to evaluate the effect of soil application of the humic preparation Humistar and/or foliar application of the potassium fertilizer Drakar on biometric features, overwintering and state of nutrition, as well as the quantity and quality of winter oilseed rape yield. This study was based on a single-factorial field experiment conducted over 2006-2009 in Chrząstowo, on mesic Typic Hapludalf soil of a granulometric composition of light loam, in a randomized block design, in four replications. The effect of the following was evaluated: Humistar (12% humic acids and 3% fulvic acids), applied pre-sowing into soil, at a rate of 40 dm³∙ha^-1 (T1); Drakar (25.7% K and 3% N), applied in autumn after formation of 6 leaves (2 dm³∙ ha^-1) and in spring, at the beginning of falling petals (4 l∙ha^-1) (T2); combined application of Humistar and Drakar (T3); and the control (T4). In this study has been shown that Drakar had a positive effect on seed yield of oilseed rape. The use of this fertilizer increased the chlorophyll index in the autumn and improved overwintering in relations to the control only when the earlier application of Humistar was made. Further studies are necessary to evaluate the effect of these preparations in weak soils with low content of organic matter and nutrients.

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