Yield Components and Nutritive Value of Black Locust and Mimosa in Arkansas, USA D.M. Burner 1, D.J. Carrier 2, D.P. Belesky 3, D.H. Pote 1, A.Ares 4, and E.C. Clausen 2 1 USDA-ARS, Booneville, AR; 2 University of Arkansas, Fayetteville; 3 USDA-ARS, Beaver, WV; 4 Oregon State University, Corvallis MATERIALS & METHODS Study conducted in , trees were 3-yr-old at initiation. Spacing 0.9 x 0.9 m (12,300 trees ha -1 ). Harvested four trees per plot in July, August, September 2004 and Measurements: Stalk number Leaf dry mass Stalk basal diameter Mass leaf -1 Shoot dry mass Biomass (shoot + leaf) Number of leavesLeaf and bark mimosine (mimosa) Leaf IVDMD, TNC, N, N digestibility Leaf and bark in vitro, cellular toxicity Leaf and bark robinin (black locust) RCB with 3 replications ANOVA was by mixed linear model Harvest date within year was repeated measure Means compared by Tukey’s HSD, P < 0.05 ABSTRACT Black locust (Robinia pseudoacacia) and mimosa (Albizia julibrissin) could be used to provide summer browse. Black locust exceeded mimosa for every yield component (foliage mass tree -1, leaves shoot -1, shoots tree -1, shoot mass tree -1, basal area, and biomass tree -1 ) except mass leaf -1. Projected foliar yields were 1900 and 1600 kg foliage ha -1 for black locust and mimosa, respectively, assuming a population of trees ha -1. Mimosa foliage had greater IVDMD, TNC, and N digestibility than black locust. Mimosa foliage exceeded the nutritional N requirements of growing cattle and goats, but protein supplementation would be needed for growing goats grazing black locust foliage. Concentrations of robinin and mimosine were below detectable limits in black locust and mimosa, respectively. The extract of black locust bark, but not foliage, was toxic to bioassayed monkey cells. Either black locust or mimosa could provide moderate quantities of high quality, rotationally grazed forage for cattle or goats during summer months when herbaceous forage may in short supply. OBJECTIVE Determine foliar yield components and nutritive value (in vitro digestibility [IVDMD], total nonstructural carbohydrate [TNC], N, robinin, and mimosine) of transplanted trees pollarded at 50 cm. INTRODUCTION Black locust (subfamily Faboideae) and mimosa (subfamily Mimosaceae) are tree species in Fabaceae that could be used for livestock browse in the USA and other countries. Both species are invasive in some ecosystems, and their browse is highly preferred by goats (Luginbuhl and Mueller, 1999). The feed value of black locust leaves has been debated for some time mainly because of the presence of anti-quality components. Black locust is toxic to horses but not to goats (Cheeke, 1992). It is not known if black locust is toxic to cattle or sheep. Less is known about the nutritive value of mimosa than black locust. Mimosa leaves have less neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude protein (CP), and is less preferred by goats than black locust (Addlestone et al. 1999). Data are limited on secondary metabolites in either species. The non-toxic flavonoid robinin (kaempferol-3-O-robinoside-7-O-rhamnoside), a complex of isomeric forms of a triglycoside, occurs in Robinia flowers, but presence in leaves is not documented. Robinin has antioxidant properties that benefit human health, and could be a value-added flavonoid extracted prior to biofuel conversion (Lau et al. 2005). Mimosine [β-N-(3-hydroxy-4-pyridone)-α-aminopropionic acid] is a toxic alkaloid present in leaves of Leucaena spp. In L. leucocephala, mimosine decreases in concentration with leaf age, from 45 g kg -1 in 1-wk-old to 2 g kg -1 in 10-wk-old leaves (Tangendjaja et al. 1986). Mimosa does not appear to have been tested for mimosine despite anecdotal evidence of its presence. RESULTS  Black locust grew more rapidly than mimosa during 2-yr establishment period.  Leaf mass tree -1 was low for mimosa in it was hotter and drier in July-August 2005 than 2004 (Fig. 1).  Projected yields were 1900 kg leaves ha -1 for black locust, and 1600 kg leaves ha -1 for mimosa based on tree density.  Mimosa had consistently more IVDMD than black locust (Fig. 2).  Black locust had more leaf N than mimosa (31.2 and 27.1 g kg -1 ), but N digestibility of black locust (49.6 to 57.3%) was much less than that of mimosa (84.4 to 92.6%)  Black locust had about half the leaf TNC as mimosa (27.8 and 59.7 g kg -1 ).  Robinin in black locust was below the detectable limit of 0.01 mg mL -1.  Mimosine in mimosa was below the detectable limit of 0.03 mg mL -1.  Black locust bark extract was cytotoxic to cultured cells since the 1:8 dilution inhibited cell viability (Fig. 3). At higher concentrations, extract color might have interfered with the MTT assay. Leaf and bark extracts of mimosa were not toxic to cultured monkey cells. REFERENCES Addlestone BJ, Mueller JP, Luginbuhl J-M (1999) The establishment and early growth of three leguminous tree species for use in silvopastoral systems of the southeastern USA. Agrofor Syst 44: Cheeke PR (1992) Black locust forage as an animal feedstuff. pp In: Hanover JW et al. (eds), Proc Int Conf. Black Locust Biol, Culture, Utiliz, June 1991, E. Lansing, Michigan. Lau CS, Carrier DJ, Beitle RR, Howard LR, Lay JO, Liyanage R, Clausen EC (2005) A glycoside flavonoid in kudzu (Pueraria lobata): Identification, quantification, and determination of antioxidant activity. Appl Biochem Biotech. 123: Luginbuhl J-M, Mueller JP (1999) Growth, leaf biomass, chemical composition and goat browsing preference of four fodder tree species. J Anim Sci 77, Suppl.1:24. Tangendjaja B, Lowry JB, Wills RBH (1986) Changes in mimosine, phenol, protein and fibre content of Leucaena leucocephala leaf during growth and development. Aust J Exp Agric 26: Table 1. Leaf-shoot comparisons for black locust and mimosa (P < 0.05). Trait Black locust Mimosa Leaves shoot -1 (no.) Leaf mass tree -1 (g) Shoots tree -1 (no.) Shoot mass tree -1 (g) Biomass tree -1 (g) Basal area tree -1 (mm 2 ) Figure 2 Figure 1 Figure 3 Mimosa Black locust Manuscript was accepted for publication in Agroforestry Systems.