Abstract

Nitrogen (N₂) fixation by Pterocarpus lucens in a natural semi arid ecosystem, in Ferlo, Senegal was estimated using ¹⁵N natural abundance (∂¹⁵N) procedure. Other non-fixing trees accompanying P. lucens in the same area were also investigated as control. Results showed an important variation of ∂¹⁵N in leaves between the nitrogen-fixing tree (P. lucens) and reference plants, whereas no significant differences were recorded in amount of nitrogen (%). The relative ∂¹⁵N values (‰) were higher in non-fixing plants than in fixing plants considered. Calculations of %Ndfa gave rates ranging between 26% and 49%. The values of %Ndfa depend largely on soil and the reference plants. The contribution of nitrogen derived from fixation in leaves reached 28.9 kg.N/ha and 10.8 kg.N/ha in ferruginous and in sandy soil respectively.

Key words: Pterocarpus lucens, ¹⁵N natural abundance, semi arid lowland, biological nitrogen fixation, natural ecosystem