Study was conducted in Donatowo near Śrem in 2004 and 2005. Field experiment was carried out at a randomised block design in four repetitions. The experimental factors were phosphorus and potassium fertilization applied at various doses with the constant nitrogen level of 180 kg N·ha^-1. Seed yields obtained in the experiment were high and significantly differed only from the absolute control. Winter rapeseed grown on soil with very high phosphorus content and average potassium content did not respond to fertilization with those nutrients. High yields also depended on good weather conditions at the critical stages of nutrient uptake. Analysis of the correlation between seed yield and the element content in rapeseed leaves at the rosette stage showed that the yield mostly depended on the nitrogen content. Moreover, the evaluation of plant nutrition carried out at the critical stage with a professional program designed for plant material interpretation showed that in the first, as well as in the second year of the experiment, calcium, phosphorus, and potassium were yield-limiting elements. In spite of a very high phosphorus content and average potassium content in the soil, plants did not uptake adequate amounts of potassium, and phosphorus content in the plants reached nearly the minimum of good supply. The highest content of oil was noted in seeds harvested from the control plot (46.7% to 49.63%).

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