Abstract

The presence of arboreal legumes in silvopastoral systems (SPS) may affect litter production and quality, and the characteristics and distribution of soil organic matter (OM). Senescent leaves from two tree legumes [Gliricidia sepium(Jacq.) Kunth ex. Walp. (Gliricidia) andMimosa caesalpiniifoliaBenth. (Sabia)] in SPS withUrochloa decumbensStapf. R. Webster (signalgrass), and from signalgrass pasture in monoculture (Signalgrass), were collected when still attached to the plant and incubated on the ground during 0, 4, 8, 16, 32, 64, 128, and 256 days. Response variables included the disappearance of dry matter (DM), OM, C, N, lignin, acid detergent insoluble nitrogen, and C:N and lignin:N ratio. Single negative exponential models were adjusted to estimate the relative decomposition rate (k). The decomposition rate (k) of DM, OM, and C was greater for Gliricidia and Signalgrass (P < 0.05) compared to Sabia, incorporating 801 g kg DMtotal-1, 850 g kg OMtotal-1, and between 840 and 860 g kg C-total(-1). Gliricidia showed greater N release rate compared to Sabia and Signalgrass, with an estimated disappearance of 23, 4, and 6 mg N g DM(-1)for Gliricidia, Sabia, and Signalgrass, respectively. Tree legumes showed lesserkfor C:N ratio and greater for lignin concentration (P < 0.05). Gliricidia had greater release of nutrients to the soil, while Sabia had slower decomposition rates, but with the potential to form a more stable OM because of more recalcitrant compounds left behind. Thekof Signalgrass was limited by the lesser N concentration and high C:N ratio in the litter, contributing to immobilization of N during litter decomposition.