African Journal of Biotechnology Vol. 1 (1), pp. 17-22, November 2002

ISSN 1684-5315  © 2002 Academic Journals  

Biological nitrogen fixation in Crotalaria species estimated using the ¹⁵N isotope dilution method

R.T. Samba¹, S.N. Sylla², M. Neyra¹, M. Gueye³, B. Dreyfus⁴ and I. Ndoye^2*

¹Laboratoire de Microbiologie des Sols IRD/ISRA/UCAD, B.P. 1386, Dakar-Sénégal

²Département de Biologie Végétale, Université Cheikh Anta Diop, B.P. 5005 Dakar, Sénégal / Laboratoire de Microbiologie des Sols IRD/ISRA/UCAD, B.P. 1386, Dakar-Sénégal

³MIRCEN-Centre IRD/ISRA/UCAD Laboratoire de Microbiologie des Sols, B.P. 1386, Dakar-Sénégal

*Corresponding author; e-mail: Ibrahima.Ndoye@ird.sn

Accepted 16 October 2002

A greenhouse experiment was conducted to measure nitrogen fixation in three Crotalaria species : C. ochroleuca, C. perrottetii and C. retusa growing in Senegal by using ¹⁵N direct isotope dilution technique. Two non-fixing plants, Senna obtusifolia and Senna occidentalis served as reference plants. The amount of nitrogen fixed two months after planting was obtained using the average of the two reference plants. The atom % ¹⁵N excess in the Crotalaria species was significantly lower than that of the reference plants, indicating that significant nitrogen fixation occurred in the three plants. Significant differences were observed between the Crotalaria species; C. ochroleuca yielded more dry matter weight and total nitrogen than did C. perrottetti and C. retusa. The % nitrogen derived from atmosphere (%Ndfa) in leaves and stems was also higher in C. ochroleuca. There was no significant difference in %Ndfa in the whole plant between the three Crotalaria species (47% to 53%). In contrast, interspecific variability was observed based on the %Ndfa. C. ochroleuca significantly exhibited the higher amount of total nitrogen fixed, equivalent to 83 kg of nitrogen fixed per hectare. Based on these data, it was concluded that C. ochroleuca could be used in multiple cropping systems in Senegal for making more nitrogen available to other plants.

Key words: Crotalaria spp, isotope dilution, ¹⁵N, nitrogen fixation, reference plant.