DYNAMICS OF NODULATION, NITROGEN-FIXATION, NITROGEN USE AND BIOMASS YIELD OVER TIME IN POT-GROWN LEUCAENA-LEUCOCEPHALA (LAM) DE WIT

The dynamics of nodulation, N-2-fixation and N use in Leucaena leucoce phala cv. K28 over time was investigated in a screenhouse at 4, 8, 12 and 16 months after planting (MAP) using the N-15-labelling method. Le ucaena had a consistently increasing pattern of nodulation, dry biomas s and nitrogen yield. A sharp rise in nodulation was observed between 12 and 16 MAP, whereas for biomass, N accumulation and N-2-fixation, a n upward surge occurred between 4 and 12 months. Nodulation, N accumul ation, N-2-fixation and biomass yield all peaked at 16MAP. Along with the steady increase in N-2-fixation throughout the 16-month growth per iod, the % N derived from the atmosphere rose from 17.9% to 61.5%, 70. 1% and 74%, equivalent to 191, 1623, 2395 and 3385 mg N-2 fixed plant( -1) at 4, 8, 12 and 16 MAP, respectively. Nitrogen assimilation from s oil and fertilizer decreased inversely to the increase in symbiotic ni trogen fixation with time.