No available data on the amount of nitrogen fixed by nodule bacteria (Rhizobium galegae) living in symbiosis with goat’s rue (Galega orientalis Lam.) encouraged the present authors to undertake applicable examinations. In 2004 in a multi-year field experiment (cultural soil) there was determined the amount of nitrogen from the reduction of N₂ with the isotopic dilution method. It was possible due to the application of ¹⁵N at the dose of 2 g per 1 m² in a form of CO (¹⁵NH₂)₂ enriched with 12.12 at %¹⁵N to goat’s rue and maize at the beginning of the vegetation period. The samples of goat’s rue were taken at the following stages: budding, flowering, end of flowering and full ripeness. The leaf, stem and pod yields were determined and the total nitrogen at %¹⁵N was defined as well as the amount of N fixed from the air was calculated. The mean yield of goat’s rue leaves reached 8.6 t·ha^-1 of dry matter, of stems – 6.4 t·ha^-1 of dry matter, and pods – 0.2 t·ha^-1 of dry matter. The content of nitrogen in respective plant parts was as follows: in leaves – 32.7 g·kg^-1, stems – 16.1 g·kg^-1 and in pods 45.0 g·kg^-1. The amount of nitrogen fixed by goat’s rue aboveground parts was 312.3 kg N·ha^-1, which accounted for 89.2% of total nitrogen.

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