Nitrogen Fixation in Legume Trees : Measurement Based on 15N Techniques

Abstract

A field experiment has been conducted to measure the N2-fixation in six legume trees, namely Gliricidia sepium (F1), Sesbania sesban (F2), Caliandra tetragona (F3), Flemengia conges-7ta (F4), Acacia mangium (F5), and Leucena leucocephala (F6), using 15N techniques, e.g. the isotope dilution method. For this technique a reference tree, that is a non N2-fixing tree has to be used. In this experiment three reference trees were planted, but only one was used, which above ground growth was equal to the legume trees. The reference tree chosen was Eucalyptus alba (R1). Data obtained from this experiment show that in general the legume trees have growth then the reference trees expreesed, in dray weight of various plant parts and plants and total-N uptake (TN). At harvest some of the legume and reference tree have reached a 2.5m height. The percentage of N2-fixation (%-Fix) ranged from 50 to 70%. The highest %N-Fix was shown by Leucena leucocephala (F6) (70%N-Fix). Hight %N-Fix does not necessarily mean high N-Fix uptake (gn/tree) too. The N-Fix appears to be determined by the TN (gn/tree). The highest N-Fix was contributed by the leaves, which also has the highest percentage of total –N (%TN) compared to the orther plant parts, i.e. roots, stem, and branches.