In the period of 2004-2005 researches were done at the Agricultural Experimental Station in Bałcyny (53^o35’ N; 19^o51’ E) of the University of Warmia and Mazury to determine the results of conversion of oat growing from the conventional system to the organic one. In the first crop rotation it was cultivated according to the principles of the conventional cropping system, applying mineral fertilizers and pesticides. In the second one, a two-year period of conversion of crops to the organic system was realized. In the conventional cropping and in the plot being converted to the organic one naked-grain oat cultivar was sown in the fields after winter wheat. In the conventional crop rotation, as mean from 2 years, 4.81 t∙ha^-1 of oat grain was obtained. The conversion of its growing to organic system decreased the yield by 28.7%. The decrease in grain yield was accompanied by the worsening of all the morphometric elements of the crops and yield structure. The content of protein and P in oat grain in the field of cropping converted to organic system was lower, whereas the contents of K and Mg were higher than those in the field with conventional cropping. The content of Ca was identical in oat grains coming from the two cropping systems.

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