An analysis was carried out into yielding capacity and nutritive value of pure and mixed sowings of leguminous and graminoid crops cultivated under conditions of steppe and forest-steppe zones of Western Siberia. Investigations were conducted in 2013-2015. As to climatic resources, the forest-steppe zone is a moderately warm, insufficiently moistened agroclimatic region; the steppe zone is a sharply continental climatic region with hot summer and cold winter. The indices of competitive ability and biological efficiency of annual legume-and-grass mixtures were determined depending on component ratio. As compared with the pure sowings, the mixtures yielded to them in productivity by 13-15%, but they were more plastic to weather conditions. There was established the optimum ratio of gramineous and leguminous components in mixtures equal to 70:40 % from a total seeding rate. The best crops for mixtures were found to be oats and barley, the use of wheat having reduced the total yielding capacity by 10-14%. The mixed sowings possessing a high biological productivity potential were characterized by considerable fluctuations in yields. In dry years, gramineous component formed up to 90% of yield, and 10% were for leguminous one. Under conditions of wet year, a part of leguminous component made up 40-55% of the mixture yield. The ixtures exceeded the pure sowings of oats and barley in digestible protein availability by 23-28 g per fodder unit. The zootechnic standard is reached, when the mixture yield contains 15% of leguminous component.