© 2000 Heron Publishing—Victoria, Canada
Influence of forage harvesting regimes on dynamics of biological dinitrogen fixation of a tropical woody legume
Pekka Nygren (1, 2), Pablo Cruz (1, 3), Anne Marie Domenach (4), Victor Vaillant (5) and Jorge Sierra (1)
1. INRA, Centre Antilles-Guyane, Unité Agropédoclimatique, Domaine Duclos,
F-97170 Petit-Bourg, Guadeloupe / 2. Tropical Silviculture Unit, Department of Forest Ecology, Box 28, FIN-00014 University of Helsinki, Finland (pekka.nygren@helsinki.fi) / 3. INRA, Centre Toulouse, Station d'Agronomie, B.P. 27, F-31326 Castanet Tolosan Cedex, France / 4. Laboratoire d'Ecologie Microbienne du Sol, UMR 5557, Université Lyon I, 43 Bd. du 11 novembre 1918, F-69622 Villeurbanne,
France / 5. INRA, Centre Antilles-Guyane, Unité des Recherches en Production Végétale, Domaine Duclos, F-97170 Petit-Bourg, Guadeloupe / Received July 29, 1998
Summary
Effects of three forage harvesting regimes—total removal of foliage and branches once (T-12) or twice a year (T-6) and 50%
removal every 2 months (P-2)—on growth and biological dinitrogen fixation of Gliricidia sepium (Jacq.) Walp were studied under subhumid tropical conditions in Guadeloupe, French Antilles. Gliricidia sepium was grown in association with the perennial C4 grass Dichantium aristatum (Poir) C.E. Hubbard in a two-storied fodder production system. The medium-term effects of pruning on N2 fixation were assessed by the 15N natural abundance method. Gmelina arborea Roxb. was used as the non-fixing reference. The trees in the T-12 regime followed the natural phenological cycle, and flowering
and podfilling at the beginning of the dry season reduced both foliage and nodule biomass. The T-6 regime impeded flowering,
and only a few flowers, on older branches, were produced in the P-2 regime. In trees in the T-12, T-6, and P-2 regimes, fixed
N comprised 54–87, 54–92, and 60–87%, respectively, of the total N in aboveground biomass, depending on sampling date. Total
annual accumulation of N in harvestable aboveground biomass was highest in trees in the T-6 regime at 313 kg ha–1, of which 204 kg ha–1 of N was fixed from the atmosphere. In all treatments, about 70% of the N exported per year from the plot in the fodder harvest
came from N2 fixation. Thus, N2 fixation makes an important contribution to the N economy of the G. sepium–D. aristatum forage production system, and greatly reduces the need for fertilizer application.
Keywords:
agroforestry, Gliricidia sepium, 15N natural abundance, nodulation, phenology, pruning.
