Arboreal Legume Litter Nutrient Contribution to a Tropical Silvopasture

Abstract

Legumes contribute to pasture sustainability through symbiotic N2 fixation, which may increase primary productivity and animal performance in low‐input systems. Litterfall is the main way of cycling nutrients from tree legumes. We quantified gliricidia [Gliricidia sepium (Jacq.) Kunth ex Walp.] and sabiá (Mimosa caesalpiniifolia Benth) litter deposition, along two 336‐d cycles, in a signalgrass (Brachiaria decumbens Stapf.) pasture. Litterfall was produced throughout the year but concentrated in the dry season. Sabiá produced slightly greater (P < 0.0001) litterfall amounts in the two cycles (10,790 kg ha−1) than gliricidia (10,420 kg ha−1) but the overall average N concentration of gliricidia (21.5 g kg−1) was greater than that of sabiá (18.8 g kg−1). Nitrogen amounts cycled through the litter were greater for gliricidia in both cycles (105 and 109 kg N ha−1) than for sabiá (87 and 98 kg N ha−1). The proportions of litter N that were derived from the atmosphere by symbiotic fixation were similar (P ≥ 0.05) in both species (55%) and varied little along the two cycles. Lignin concentration, which influences decomposition, was similar in both species, averaging 238 and 214 g kg−1 in the two cycles for gliricidia and 233 and 246 g kg−1 for sabiá. Greater N concentration, lower C/N ratio and lower lignin concentration indicate that gliricidia litter may have a faster cycling rate than sabiá litter. Sabiá could be a more promising species for soil cover and protection because of its slower litter decomposition rate.Core Ideas Litter deposition was an important pathway of N return in warm‐climate silvopasture systems. Tree legumes added significant amounts of biological nitrogen fixation to silvopasture systems. Gliricidia litter presented better quality than Mimosa litter. Proportion of litter N derived from atmosphere was significant.