Dynamics of nodulation,nitrogen fixation,nitrogen use and biomass yield over time in pot-grown Leucaena leucocephala (Lam.) de Wit

The dynamics of nodulation, N₂-fixation and N use in Leucaena leucocephala cv. K28 over time was investigated in a screenhouse at 4, 8, 12 and 16 months after planting (MAP) using the ¹⁵N-labelling method. Leucaena had a consistently increasing pattern of nodulation, dry biomass and nitrogen yield. A sharp rise in nodulation was observed between 12 and 16 MAP, whereas for biomass, N accumulation and N₂-fixation, and N₂-fixation, an upward surge occurred between 4 and 12 months. Nodulation, N accumulation, N₂-fixation and biomass yield all peaked at 16 MAP. Along with the steady increase in N₂-fixation throughout the 16-month growth period, 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 N₂ fixed plant^-1 at 4, 8, 12 and 16 MAP, respectively. Nitrogen assimilation from soil and fertilizer decreased inversely to the increase in symbiotic nitrogen fixation with time.