In 1999-2002 a strict field experiment was established in split-block design with control object at the Mochełek Experimental Station of the Faculty of Agriculture, University of Technology and Agriculture. Plants of traditional yellow lupin cultivar ‘Polo’ were sprayed with Topflor 15 SC (15% flurprimidol), which is a pirymidine growth regulator. Two dates of Topflor application, once – at the beginning of plant budding and at the beginning of flowering, twice – at the beginning of plant budding and flowering constituted the first factor. Topflor was applied at three doses – 0.15; 0.30 and 0.45 dm^3.ha^-1, which constituted the second factor. There was observed neither a significant effect of the date nor of the dose of Topflor application on yellow lupin seed yield and structural yield components. Topflor affected neither the plant height nor the straw yield. The seed structure according to their thickness as well as protein content in seeds were affected neither by the date of application nor the dose of Topflor. Only a significant increase in the value of yellow lupin harvest index and seed weight in pods developed on branches were a result of a favorable effect of Topflor.

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