Abstract

Tree legumes such as Gliricidia sepium (Jacq.) Kunth ex Walp. (Gliricidia) and Mimosa caesalpiniifolia Benth. (Sabia) are important options to enhance drought tolerance of livestock systems and improve the diet of grazing animals. This study assessed productive and nutritional potential of Gliricidia or Sabia in a silvopastoral system (SPS) with signalgrass [Urochloa decumbens (Stapf) R.D Webster]. Treatments were the two SPS allocated in a randomized complete block (three replications). Trees were harvested four times, with 6-month intervals between harvests. Response variables included all dendrometry measurements, dry matter of tree components, chemical composition, delta N-15, delta C-13, and N derived from the atmosphere (Ndfa). Sabia had greater basal diameter (7.6 +/- 1.2 vs. 6.0 +/- 1.2 cm; P = 0.045), shaft length (7.5 +/- 0.2 vs. 5.5 +/- 0.2 cm; P = 0.002), Lorey's height (7.2 +/- 0.3 vs. 5.9 +/- 0.3 cm; P = 0.023), tree volume (0.3 +/- 0.1 vs. 0.2 +/- 0.1 m(3); P = 0.014), intermediate branches (14 +/- 0.8 vs. 8 +/- 0.8 Mg DM/ha; P = 0.004), total leaf biomass (3053 +/- 236 vs. 1829 +/- 236 kg DM/ha; P = 0.029), dry matter concentration (427 +/- 0.4 vs. 252 +/- 0.4 g/kg; P = 0.021), lignin (233 +/- 0.7 vs. 145 +/- 0.7 g/kg DM; P = 0.001), and acid detergent insoluble nitrogen (272 +/- 1.2 vs. 168 +/- 1.2 g N/kg; P = 0.004). Gliricidia presented greater crude protein (250 +/- 0.7 vs. 187 +/- 0.7 g/kg DM; P = 0.003), more enriched delta C-13 (-34 +/- 0.2 vs. -35 +/- 0.2 parts per thousand; P = 0.006), and Ndfa (65 +/- 4 vs. 47 +/- 4 %; P = 0.041). Sabia demonstrated continued growth and potential to incorporate nutrients into the soil. Gliricidia had greater potential for biological N-2 fixation. Both tree legumes have potential for use in SPS. Gliricidia is recommended when the livestock production is the major goal. Sabia is recommended when timber production is the most desirable activity.