EFFET DU SOUFRE ET DE L’AZOTE SUR LA FIXATION SYMBIOTIQUE D’AZOTE CHEZ LES PLANTULES DE LUZERNE (Medicago Sativa L.)

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Abstract
The effect of the addition of sulphur and nitrogen on the aerial mass, root mass, nodulation and nitrogenase activity was studied on alfalfa cv. Saranac seedlings inoculated with a very efficient strain of Rhizobium meliloti. The aerial mass, root mass and a nodulation index increase with the addition of increasing concentrations of nitrogen and sulphur. The rate of increase of aerial mass and the nodulation index with sulphur are not constant over the range of the concentrations studied. Sulphur and nitrogen appeared to have a very important multiplicative effect on aerial mass and root mass. In the absence of sulphur, nitrogen did not affect nitrogenase activity. The aerial mass and the nodulation index are strongly correlated to the root mass and nitrogenase activity. However, nitrogenase activity and the root mass were not significantly correlated.