EARLY NITROGEN-FIXATION AND UTILIZATION IN ALBIZIA LEBBECK, LEUCAENA-LEUCOCEPHALA, AND GLIRICIDIA-SEPIUM USING NITROGEN (N-15) LABELING

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 currently used in alley cropping. Nitrogen fixation and utilization were assessed in a screenhouse at four months after planting by the N-15 dilution technique using Senna 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 Gliricidia and Leucaena nodules, respectively. A. lebbeck had bigger but significantly (P less than or equal to 0.05) lower number of nodules per plant than G. sepium, but it did not differ from Leucaena. Albizia was the best N2 fixer with 44% Ndfa 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 Albizia 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 Leucaena (72.5% Ndfs) and Gliricidia (63.9% Ndfs) and less on fertilizer N as well. Thus A. lebbeck appears to be a potential hedgerow species for alley cropping purpose.