Early nitrogen fixation and utilization in Albizia lebbeck, Leucaena leucocephala, and Gliricidia sepium using nitrogen (15N) labelling.
High nitrogen (N2)-fixing potential is a desirable characteristic for any candidate hedgerow tree,. Thus a study was conducted to evaluate Albizia lebbeck as a N2-fixing tree in comparison to Gliricidia sepium and Leucaena leucocephala, which are currently used in alley cropping. Nitrogen fixation and utilization were assessed in a screenhouse 4 months after planting seeds inoculated with Rhizobium, using the 15N dilution technique with Senna siamea (Cassia siamea) as the non N2-fixing reference. A. lebbeck accumulated significantly more N than L. leucocephala, but G. sepium was intermediate. This superiority in N yield was mainly due to its abundant nodule dry weight production which accounted for up to 10.8% of its total N. This was equivalent to 2.5- and 6-fold that of G. sepium and L. leucocephala nodules, respectively. A. lebbeck had a bigger but significantly (P≤0.05) lower number of nodules per plant than G. sepium, but it did not differ from L. leucocephala. A. lebbeck was the best N2 fixer with 44% Ndfa [nitrogen derived from atmosphere], equivalent to 533 mg N per plant. G. sepium followed with 28% Ndfa and L. leucocephala with 18% Ndfa corresponding to 321 and 191 mg N fixed, respectively. However, the relatively higher N2 fixation in A. lebbeck was not translated into higher N or dry matter yields. As A. lebbeck fixed more N, it depended less on soil N (49.8%) than did L. leucocephala (72.5% Ndfs [nitrogen derived from soil]) and G. sepium (63.9% Ndfs) and less on fertilizer N as well. Thus, A. lebbeck appears to be a potential hedgerow species for alley cropping purpose.