The overall objective of this thesis work, in the Yucatán peninsula (México), was to establish a system with mixed woody species (leguminous/non-leguminous) to investigate the extent to which they increase nitrogen uptake and growth. The study tested the hypothesis that such mixtures may stimulate of N₂ fixation from the atmosphere and the transfer of N from leguminous to non-leguminous plants. Three woody species were selected: Leucaena leucocephala (legume), Moringa oleifera (non-legume) and Guazuma ulmifolia (non-legume). More than 80% of planted seedlings survived and grew rapidly. Total biomass (fodder) production was 1.9-7.7 ton ha^-1 for monocrops and 6-9 ton ha^-1 for the mixtures. Nitrogen yield in the fodder was higher in the Leucaena+Guazuma mixture (285 kg N ha^-1), followed by Leucaena monocrop and Leucaena+Moringa mixture (244 and 183 kg N ha^-1, respectively). The δ¹⁵ N of samples from non-fixing species ranged from 2.7 to 3.2‰ (mean 3.0 ± 0.45‰). The δ¹⁵ N of L. leucocephala (0.8‰) was significantly lower, indicating that nitrogen fixation occurred in the Leucaena plants. The % Ndfa in the Leucaena mixtures ranged from 58 to 72% while in the Leucaena monocrop it was 69%, at 11 months old. Moringa leaves decomposed most rapidly, followed by Leucaena+Moringa, and, was best described by a double exponential model. The combination of Leucaena+Guazuma decomposed more slowly and pure Leucaena leaves decomposed at an intermediate rate. Over 16 weeks, Leucaena+Moringa released 65-75% of the initial N, Leucaena+Guazuma released 46-63%, and Leucaena leaves alone released, on average, 54% of their N. Lignin+polyphenols and tannins had a strong negative correlation with the rate of nitrogen release. The alteration of the decomposition and N release patterns observed when mixing plant materials of different quality provides good prospects for improving synchrony between N availability and plant N uptake.