ACTIVE N-2 FIXATION IN SEVERAL FAIDHERBIA-ALBIDA PROVENANCES

For tree legumes, Faidherbia albida is among those with low symbiotic capability, and for which significant improvement is needed. An experi ment was conducted in the greenhouse, using the N-15 isotope dilution technique to measure differences in the proportion (%Ndfa) and total N fixed in seven F. albida provenances grown in an Arenosol soil in Sen egal. Total dry matter and N yield values were not significantly diffe rent among the seven provenances. In contrast, significant variability was measured in N-2 fixation, with %Ndfa ranging from 0% in two prove nances to 38% in the Kabrousse provenance. Also, total N fixed was hig hest in Kabrousse, 0.44 g N plan t(-1), compared with the 0 to 0.26 g plant(-1) fixed ill the other provenances. Based on these results, Kab rousse was selected for further examination in the field, where still higher %Ndfa values were obtained, 54, 58, and 54% at 3, 6, and 15 mon ths after transplanting (MAT), respectively. These are higher than the commonly reported values of %Ndfa for F. albida, and indicate the pot ential of screening as a tool for obtaining higher N-2 fixation in NFT s. Total N fixed, unlike %Ndfa, which remained fairly constant during the three harvest periods, increased from 0.54 at 3 MAT to 1.41 g N pl an t(-1) at 15 MAT.