The present agricultural crop structure is dominated by grains (48%) and by technical plants (21%), detrimental to legumes that share only 11% of the cultivated arable area on Earth. If the area cultivated with legumes doubled, the necessary nitrogen fertilisers would reduce with 50% and production costs would reduce with 30%. The increase of areas cultivated with legumes would also balance the protein balance due to a larger amount of vegetal protein. The present paper points out the impact of nitrogen fertilisation on the nodulation capacity and on atmospheric nitrogen fixation in fodder peas (Pisum arvense L.). Research in the field of nitrogen fixation has pointed out the complexity of the impact of environmental nitrogen taken over by the plants on atmospheric nitrogen fixation. Legumes use nitrogen under nitric form (NO 3 - ), as a result of the oxidation of ammonium nitrogen (NH 4 + ) from the mineral fertilisers of from organic nitrogen. These two sources of nitrogen used by the plants (NO 3 - and fixed N 2 ) are strongly dependent on the plant species, on the bacterial pool and on the environmental factors. Literature presents a consolidated scientific opinion concerning the impact of mineral nitrogen on biological nitrogen fixation: an increase of the concentration of nitrate or ammonium correlates with a decrease of the legume nodulation activity (DAVIDSON and ROBSON, 1986; EAGLESHAM, 1989). Following this work resulted in the following conclusions: Research in the field of nitrogen fixation points out the complexity of the impact of the nitrogen taken over by the plants from the environment on atmospheric nitrogen fixation.Legumes use nitrogen under nitric form (NO 3 - ) as a result of the oxidation of ammonium nitrogen (NH 4 + ) from mineral fertilisers or from organic nitrogen. Nitrogen fertilisation also impact TN and RP plant content. Daily nitrogen fixation decreases from 0.60 mg/plant/day in the control variant to 0.05 mg/plant/day in the variant treated with N 100 , while the nitrogen fixation rate in relation to dry matter varies between 14.57 mg/g DM and 1.79 mg/g DM in the variant fertilised with N 100

fodder peas, nodosities, protein, fixed nitrogen.

Presentation: oral