The subject of the experimental research referred to a two-factor field experiment carried on at the Experimental Station in Czyrna near Krynica over a period from 2010 to 2013. The first factor included two farming systems: conventional and organic. The second factor comprised the crops grown in pure stands (oats and spring vetch grown separately) and in mixed stands (oats mixed with spring vetch). The objective of the experiment was to determine both the yielding of oats in pure stands and of oats with spring vetch in mixed stands, and the response of those mixture components to the cultivation in mixed stands. Based on the results of the experiment, it was concluded that the yield of oats grains and seeds of crops sown in pure stands and in stands mixed with spring vetch decreased by 12% under the organic farming system. The total yield of oats grains and spring vetch seeds decreased along with the decrease in the content of oats in the mixture. The growing of oats and spring vetch in mixed stands under the conventional system of farming resulted in the better yielding of oats compared to the yield of oats under the organic farming. The mixtures of oats and spring vetch were found to better utilize the habitat conditions in their mixed stands compared to those grown separately in pure stands.