Biological nitrogen fixation in four Gliricidia sepium genotypes

Abstract

A field experiment was conducted at the Coconut Research Institute in Sri Lanka to examine the biological nitrogen fixation potential of three Gliricidia sepium provenances (OFI 14/84, 17/84, 12/86) and a local landrace (designated LL), using the 15N isotope dilution method. There was marked variation in dry matter, total N, nodulation and 15N enrichment among the Gliricidia genotypes (= 0.001), and the dry matter yield of Cassia siamea (syn. Senna siamea), the non-N2 fixing reference plant was higher than for G. sepium. In all cases, highest biomass and total N were aboveground, with roots on average accounting for < 20 % of total dry matter or the total N in plants. Atom % 15N excess was highest in C. siamea, and lowest in OFI 14/84. Although atom % 15N excess was lower in Gliricidia leaves than in the other organs (all of which had similar 15N enrichments), values of % N derived from atmospheric N2 fixation ( % Ndfa) calculated for any individual organ or for the whole plant were similar. This was because the relative distribution of 15N in the different parts of the fixing plant followed the same trend as in the reference plant. There were significant differences (p = 0. 01) in N2 fixation between the Gliricidia genotypes.The values ranged from 17.8 g N tree -I (equivalent to 86 kg N ha -l at 5000 trees ha -1) in OFI 12/86 to 61.7g N tree -~ (equivalent to 309 kg N ha -1) in OFI 14/84. Although most of this variability was due to differences in both % Ndfa and total N in plant, amount of N fixed was more correlated with total N in plant (r = 0.935) than with % Ndfa (r = 0.707). On average, % Ndfa in all three G. sepium provenances and LL was about 55 % or 34.6 g N tree-l (equivalent to some 166 kg N ha-l) in the 9 months within which N2 fixation was measured. This represents a substantial contribution of N into the soil-plant system. SamplingPlants were separated into roots, stem, branches and leaves, which were chopped into 1-5 cm pieces, and then weighed fresh. A 300 g sub-sample was taken for drying at 70°C to constant weight in a forced-draft

Mixed-species plantations of Acacia mangium and Eucalyptus grandis in Brazil

“…By contrast, in the 15 N dilution experiment, there were lower discrepancies in the estimates of N 2 fixation when %Ndfa was assessed from the AE of leaves only. That finding was consistent with the low within-tree AE variability found by Parrotta et al (1994a) and Liyanage et al (1994). In such cases, the use of foliar AE instead of whole-tree AE would not be too detrimental for obtaining an accurate estimate of N derived from atmospheric N 2 .…”

“…High rates of 15 N enrichment (5-10% 15 N atom excess) are usually used in 15 N dilution experiments (Liyanage et al, 1994;Parrotta et al, 1994a,b;Guinto et al, 2000). High AE Ffinal and AE REFfinal are then observed, and can be measured with a low sensitivity mass spectrometer.…”

Enhancing legume N2 fixation through plant and soil management

“…eData derived from LeAgard et al (1990). fData for Gliricidia (Gliricidia sepium) are derived from Liyanage et al (1994). gna -data either not avialable or not appropriate.…”

Dinitrogen-fixation by three neotropical agroforestry tree species under semi-controlled field conditions

“…Recent studies based on either natural abundance of the stable 15 N isotope (Ladha et al 1993;Nygren et al 2000;Peoples et al 1996) or labelling with 15 N (Liyanage et al 1994;Peoples et al 1996;Stå hl et al 2002Stå hl et al , 2005 have shown considerably higher N 2 fixation potential of several tree species used in agroforestry. Several Inga spp.…”