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In Florida, rhizoma peanut (RP; Arachis glabrata Benth.), a tropical legume, combines the attributes of excellent nutritive value, competitive ability with tropical grasses, and high animal performance. The objective of this study was to determine the effects of spring N fertilization (0 vs 35 kg/ha) and summer stocking rate (1.5 and 2.5 bulls/ha) on herbage mass, nutritive value, herbage allowance, and diet botanical composition of grazed RP-grass swards and their interaction with growth and development of bulls (Senepol, and Brahman or Angus). The study was conducted in 1995 and 1996 at the USDA, ARS, Subtropical Agriculture Research Station in Brooksville, FL. Nitrogen was applied in April of each year, and all pastures were stocked with 1.5 bulls/ha until approximately July of each year, when stocking rate was increased on half the pastures to 2.5 bulls/ha. Herbage mass (HM, kg/ ha), herbage allowance (HA, kg/kg BW), nutritive value (CP and in vitro organic matter digestibility [IVOMD]), and diet botanical composition (fecal microhistological) readings were determined. Animal measurements included total and seasonal (spring vs summer), ADG, hip height (cm), scrotal circumference (SC, cm), and plasma urea nitrogen (PUN, mg/dL). Herbage mass (3.0 [+ or -] 0.12 Mg/ha and 3.4 + 0.13 Mg/ha in 1995 and 1996, respectively) was not affected by nitrogen fertilization or stocking rate but was affected by season (P [is less than] 0.05) due to increased plant growth rate associated with summer rainfall. Stocking rate did affect herbage availability, but it never fell below 3 kg/kg BW, indicating herbage availability was never limiting. Crude protein (200 to 140 g/kg) and IVOMD (650 to 540 g/kg) were not affected by treatment, but declined (P [is less than] 0.001) from spring until fall. Treatments also had no effect on diet botanical composition. Summer ADG averaged about 0.2 kg/d lower than spring ADG, due, in part, to seasonal declines in nutritive value. Because herbage allowance was never limiting, full-season ADG was not affected by stocking rate or N fertilization and averaged 0.61 [+ or -] 0.03 and 0.60 [+ or -] 0.02 kg/d in 1995 and 1996, respectively. There were season x breed interactions (P [is less than] 0.05) for ADG due to greater declines during the summer for Angus than for Senepol or Brahman. There were no differences in final BW, SC, BCS, hip height, or PUN due to treatments, but breed differences were noted (P [is less than] 0.05) for all measures except BCS. Key Words: Fertilization, Food Preferences, Stocking Density

Atmospheric [CO.sub.2] and temperature may significantly modify plant production. Grasslands occupy in excess of 25% of the Earth's land area, but grassland species have received limited attention from researchers studying climate change. A 3-yr study was conducted to determine the effects of elevated atmospheric [CO.sub.2] and temperature on dry matter (DM) harvested from the [C.sub.3] legume `Florigraze' rhizoma peanut (RP, Arachis glabrata Benth.) and the Ca grass `Pensacola' bahiagrass (BG, Paspalum notatum Flugge). Both species were field grown in Millhopper fine sand (loamy siliceous Grossarenic Paleudult) in temperature-gradient greenhouses under different [CO.sub.2] (360 and 700 µmol [mol.sup.-1]) and temperature conditions (baseline [B], B+1.5, B+3.0, and B+4.5 ° C, where B equaled ambient temperature). Plots (2 by 5 m) were harvested three times in 1996 and four times each in 1997 and 1998. Analyzed across years, yield increased 25% for RP (P = 0.02) and tended to increase for BG (15%; P = 0.18) with the near doubling of [CO.sub.2], but there was species by [CO.sub.2] interaction (P = 0.06) as a result of the greater response to [CO.sub.2] by the [C.sub.3] legume. There was a positive effect of increasing temperature on yield of both species. Averaged across species, yield increased 11% in 1996, 12% in 1997, and 26% in 1998 as temperature increased from B to B+4.5 ° C. Under well-watered conditions in this experiment, elevated [CO.sub.2] increased DM harvested of a [C.sub.3] legume and tended to increase that of a [C.sub.4] grass, while the yield response to increasing temperature was positive for both species., ATMOSPHERIC [CO.sub.2] has steadily increased from preindustrial concentrations of 280 µmol [mol.sup.-1] and is predicted to double by the end of the 21st century (Barnola et al., 1994; Keeling and [...]

Seasonally low N concentrations in `Floralta' limpograss [Hemarthria altissima (Poir.) Stapf & C.E. Hubb.] limit intake and weight gain of growing animals. This research evaluated management alternatives for increasing summer weight gains of beef replacement heifers (Bos spp.) on limpograss pastures in Florida. Soils were sandy, siliceous, hyperthermic, aeric (Smyrna series) or ultic (Pomona series) Haplaquods. During 1992 and 1993, a factorial arrangement of two pasture N fertilization rates (50 and 150 kg [ha.sup.-1]) and three diet supplements (NONE, corn [Zea mays L.] plus urea [CUI, and CU plus rumen undegradable protein [CUUP]) were studied in two replications of a completely randomized design. Supplementation with CU increased average daily gain (ADG) from 0.06 (NONE) to 0.41 kg on pastures fertilized with 50 kg N [ha.sup.-1], but there was no ADG response to CU when N rate was 150 kg [ha.sup.-1] When no supplement was fed, increasing pasture N fertilization from 50 to 150 kg [ha.sup.-1] increased ADG from 0.06 to 0.36 kg. Grass crude protein (CP; 73 vs. 56 g [kg.sup.-1]) and in vitro organic matter digestion (IVOMD; 542 vs. 509 g [kg.sup.-1]) were greater at the higher N rate. Heifer plasma urea N (PUN) concentration was low (4.2 mg d[L.sup.-1]) when no supplement was fed and pastures received 50 kg N [ha.sup.-1], suggesting that low CP was limiting ADG. These data indicate that N deficiencies of cattle grazing limpograss can be overcome by increasing rate of pasture N fertilization or by providing N supplements., WARM-SEASON PERENNIAL GRASSES used as pasture or hay in Florida often do not meet the nutrient requirements of growing ruminants (Moore, 1992). Floralta limpograss is an important perennial forage in [...]

Sand blackberry (Rubus cuneifolius Pursh) is a troublesome perennial weed in Florida rhizoma peanut (Arachis glabrata Benth.)-grass pastures. The degree to which it can be controlled by defoliation is not well understood. In 2011 and 2012, blackberry regrowth and persistence responses were assessed by clipping every 35 d to three stubble heights (8, 16, and 24 cm), with or without simultaneous removal of all leaf from remaining stubble. Blackberry dry matter harvested decreased linearly (12.8 to 8.5 g m-2) as clipping stubble height increased when remaining stubble leaf was removed, but there was a linear increase in blackberry harvested with increasing clipping stubble height (12.1 to 26.0 g m-2) if remaining stubble leaf was not removed. Across stubble heights, cumulative change in blackberry cover across the 2 yr was -15% units if stubble leaf was removed compared with +1% unit when leaf remained intact. As stubble height increased from 8 to 24 cm, blackberry cover increased linearly, both when stubble leaf was removed (-18 to 0% units, respectively) and when leaf remained intact (-12 to +17% units, respectively). In Year 1, blackberry stem density decreased 10 stems m-2 when stubble leaf was removed and 4 stems m-2 when leaf remained intact, but there was no effect of leaf removal in Year 2. Both clipping stubble height and removal of leaf mass affected blackberry regrowth and cover responses, suggesting that combining leaf removal by browsing animals with periodic close mowing will reduce blackberry cover, mass, and stem density. [ABSTRACT FROM AUTHOR]