Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2007
Publication Date: 1/1/2008
Citation: Burner, D.M., Pote, D.H., Carrier, D.J., Belesky, D.P., Ares, A., Clausen, E.C. 2008. Yield components and nutritive value of Robinia pseudoacacia and Albizia julibrissin in Arkansas, USA. Agroforestry Systems. 72(1):51-62.
Interpretive Summary: Available supplies of conventional grass and legume forages can become limiting during hot, dry summer periods, necessitating expensive, supplemental hay feeding to livestock. Common but unconventional forages, such as deep-rooted tree legumes, can improve the feed deficit for certain livestock production systems. We clipped black locust and mimosa tress at 20” height to stimulate shoot production and measured leaf and woody stem yields; leaf feed value, presence of secondary compounds, and cellular toxicity. Black locust surpassed mimosa in most yield parameters, but mimosa surpassed black locust in leaf feed value. Black locust bark, but not leaves, caused cell toxicity. Mimosa leaves and bark caused no cellular toxicity. Either species could be utilized for forage, although black locust should not be fed to horses. Black locust is primarily recommended for goats, which are highly productive browse species and are not harmed by the toxic compounds found in the bark, but supplemental protein might be needed for maximum weight gain. There is insufficient information to recommend black locust for other livestock species. This study supports our previous report in which we demonstrated the summer productivity of black locust. These results are of interest to other scientists, extension personnel, and ranchers because they show that either black locust or mimosa could provide moderate quantities of high quality, rotationally grazed forage for goats during summer months when conventional forages are in short supply.
Technical Abstract: Ranchers need alternative livestock feeds when herbaceous forages become limiting in summer. Our objectives were to determine: 1) leaf and stem biomass components, 2) nutritive value (in vitro dry matter digestibility [IVDMD], total nonstructural carbohydrate [TNC], N and N digestibility) of leaves for animal browse, 3) concentration of the secondary metabolites robinin and mimosine, and 4) in vitro leaf and bark toxicity for black locust (Robinia pseudoacacia L.) and mimosa (Albizia julibrissin Durz.), respectively, pollarded at 50 cm in Arkansas, USA. Black locust exceeded mimosa for every yield component (leaf mass/tree, leaves/shoot, shoots/tree, shoot mass/tree, stem basal area, and biomass/tree) except mass/leaf. Projected yields were 1900 and 1600 kg leaves/ha. Mimosa leaves had greater IVDMD, TNC, and N digestibility than black locust. Mimosa leaves exceeded the nutritional N requirements of growing cattle (Bos taurus L.) and goats (Capra hircus L.), but protein supplementation would be needed for growing goats grazing black locust leaves. Concentrations of secondary metabolites robinin and mimosine were below detectable limits in black locust and mimosa, respectively. The extract of black locust bark, but not leaves, was toxic to bioassayed African green monkey (Cercopithecus aethiops L.) cells. Either black locust or mimosa could provide moderate quantities of high quality, rotationally grazed forage for goats during summer months when herbaceous forage may in short supply.