Legume proportion affects bahiagrass–rhizoma peanut mixture production and nutritive value and legume composition of cattle diets

Abstract

Our objectives were to (1) quantify the effects of legume proportion on herbage accumulation (HA) and nutritive value of pasture mixtures compared with grass monocultures receiving typical or no N fertilizer application and (2) compare animal selection measures in legume–grass mixed pastures using microhistological and δ13C techniques applied to fecal samples. We evaluated HA and nutritive value in 2 grazing systems: (1) mixtures of Florigraze rhizoma peanut (Arachis glabrata Benth.) and Pensacola bahiagrass (Paspalum notatum Flügge) (MIX-SYS; 6 to 78% legume, grazed to a 15-cm stubble height at 42-d grazing intervals and ~7-d residence periods) and (2) bahiagrass monocultures receiving no N or 50 kg of N/ha per year (BG-SYS and BGN-SYS, grazed to 10-cm stubble height at 21-d grazing intervals with ~7-d residence periods) over 2 yr. Animal [~220 kg, 12-mo-old Brahman (Bos indicus) × Angus (Bos taurus) heifers] diet selection in MIX-SYS was quantified using microhistological and δ13C techniques applied to fecal samples. Herbage in vitro digestible OM (IVDOM) and CP concentrations increased linearly with increasing legume proportion in MIX-SYS up to ~45%, but MIX-SYS HA decreased linearly with increasing legume proportion. Treatment MIX-SYS had greater average HA [5,920 ± 271 (SE) kg/ha vs. 4,890 ± 236 kg/ ha for monocultures] and nutritive value than BG-SYS and BGN-SYS (CP of 12.9 ± 0.7% and IVDOM of 55.8 ± 1.0% for MIX-SYS vs. 9.1 ± 0.4% and 50.7 ± 1.5%, respectively, for monocultures). Results of microhistological and δ13C techniques applied to fecal samples were highly and positively correlated with sward canopy legume proportion, but fecal δ13C tracked legume proportion in the pasture more closely than the microhistological technique. Benefits of legumes to HA and nutritive value were observed at low legume participation, but they did not increase proportionally as legume percentage increased above ~45%. These results support a conclusion that relatively small proportions of legumes have measurable positive effects on important grassland characteristics.