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Seasonal Changes in the Herbage Mass and Quality of Legume-Bahiagrass Pastures


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SEASONAL CHANGES IN HERBAGE MASS AND QUALITY OF LEGUME-BAHIAGRASS PASTURES By MARIA YOLANDA CASTELO IPIALES A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003

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Copyright 2003 By Maria Yolanda Castelo Ipiales

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Dedicated to my husband, Jose Luis; my father, Teofilo, and my mother, Aida.

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ACKNOWLEDGMENTS The author wishes to express her sincere thanks and appreciation to Dr. Martin Adjei (chair of her supervisory committee) for all his help and guidance throughout the fieldwork and graduate program. Appreciation is also extended to Drs. Carrol Chambliss, Lynn Sollenberger, John Arthington, and Nick Place (members of the supervisory committee) for their advice. The author acknowledges the help given to her during the research by the personnel at the Range Cattle REC in Ona, Florida. Special acknowledgement is due to the authors husband, Jose Luis, for his invaluable help and love. Finally, sincere appreciation is extended to the authors family for their understanding and encouragement. iv

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TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES............................................................................................................vii LIST OF FIGURES...........................................................................................................ix ABSTRACT.........................................................................................................................x CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................4 Characterization of Species..........................................................................................4 Bahiagrass (Paspalum notatum Flgge)................................................................4 Aeschynomene Evenia (Aeschynomene evenia C. Wright)...................................6 Shaw Creeping Vigna (Vigna parkeri Baker).......................................................7 Grass-Legume Mixtures...............................................................................................8 Forage Quality............................................................................................................10 Grazing Systems.........................................................................................................11 Grazing Management..........................................................................................11 Continuous Stocking...........................................................................................12 Rotational Stocking.............................................................................................13 Grazing Intensity.................................................................................................13 Herbage Allowance.............................................................................................14 Nutritive Value...........................................................................................................16 3 MATERIALS AND METHODS...............................................................................18 General Description of the Experimental Area..........................................................18 Experimental Procedures............................................................................................18 Legume-grass Mixture.........................................................................................18 Pasture Establishment..........................................................................................19 Treatment and Experimental Design...................................................................19 Pasture Samples..........................................................................................................20 Grazing Experiment.............................................................................................20 Botanical Composition........................................................................................21 Chemical Composition........................................................................................21 v

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Animal Performance...................................................................................................22 Statistical Analysis......................................................................................................24 4 RESULTS AND DISCUSSION.................................................................................26 Forage Responses.......................................................................................................26 Herbage Mass of Sward Components.................................................................26 Bahiagrass....................................................................................................26 Evenia...........................................................................................................27 Creeping vigna.............................................................................................27 Botanical Composition........................................................................................27 Evenia-bahiagrass.........................................................................................27 Creeping vigna-bahiagrass...........................................................................28 Density.........................................................................................................28 Crude Protein.......................................................................................................28 Bahiagrass....................................................................................................28 Evenia...........................................................................................................29 Creeping vigna.............................................................................................30 In Vitro Organic Matter Digestibility..................................................................30 Bahiagrass....................................................................................................30 Evenia...........................................................................................................31 Creeping vigna.............................................................................................31 Tissue Mineral Composition...............................................................................32 Bahiagrass....................................................................................................32 Evenia...........................................................................................................32 Creeping vigna.............................................................................................33 Animal Performance...................................................................................................33 5 SUMMARY AND CONCLUSIONS.........................................................................45 APPENDIX........................................................................................................................47 LIST OF REFERENCES...................................................................................................56 BIOGRAPHICAL SKETCH.............................................................................................62 vi

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LIST OF TABLES Table page 3.1. Millimeters of rainfall by month in 2001, 2002, and 61-yr average at the Range Cattle REC................................................................................................................25 4.1. Monthly HM (kg ha-) of evenia stems and leaves (leaves and stems <3 mm) in year 2001..............................................................................................................40 4.2. In vitro organic matter digestibility (g kg-) of the bahiagrass component for treatments and month in 2001..................................................................................41 4.3. Monthly tissue chemical composition of the bahiagrass component in 2001 and 2002..........................................................................................................................42 4.4. Tissue chemical composition of evenia leaves and stems in year 2001...................43 4.5. Tissue chemical composition of creeping vigna in year 2002.................................44 A.1. Herbage mass (kg ha-) of the bahiagrass component for pasture treatments by month in 2001...........................................................................................................47 A.2. Herbage mass (kg ha-) of the bahiagrass component for pasture treatments by month in 2002...........................................................................................................47 A.3. Mean CP (g kg-) of the bahiagrass component for pasture treatments by month in 2001...........................................................................................................48 A.4. Mean CP (g kg-) concentration of the bahiagrass component for pasture treatments by month in 2002....................................................................................48 A.5. Seasonal changes in (CP g kg-) concentration in evenia and creeping vigna plants in 2002...........................................................................................................49 A.6. In vitro organic matter digestibility (g kg-) of the bahiagrass component for treatments and month in 2002..................................................................................50 A.7. In vitro organic matter digestibility (g kg-) of evenia stems (> 3 mm) in 2001......50 A.8. Seasonal changes on IVOMD (g kg-) of evenia and creeping vigna plants in 2002......................................................................................................................51 vii

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A.9. Tissue chemical composition of the bahiagrass component for treatments in 2001 and 2002......................................................................................................52 A.10. Tissue chemical composition of evenia in 2002......................................................52 A.11. Monthly HM, SR, and cumulative ADG with a variable herbage allowance in 2001......................................................................................................................53 A.12. Monthly total HM, herbage accumulation (HA), SR, and cumulative ADG with a constant herbage allowance of 10 kg DM (100 kg BW) dfor evenia-bahiagrass (EB), creeping vigna-bahiagrass (CVB) and pure bahiagrass (B) pastures in 2002........................................................................................................54 viii

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LIST OF FIGURES Figure page 4.1. Monthly HM of the bahiagrass component across treatments in 2001.Means (bars) with different letters above them are different by PDIFF (P<0.05)...............35 4.2. Monthly HM of the bahiagrass component across treatments in 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05)...............36 4.3. Mean CP of the bahiagrass component across treatments in 2001. Means (bars) with different letters above them are different by PDIFF (P<0.05).........................37 4.4. Mean CP concentration in the bahiagrass component across treatments in 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05)...38 4.5. Mean CP concentration in evenia leaves and stems in 2001. Means within a plant part with a different letter above the bar are different by PDIFF (P<0.05)..............38 4.6. Mean in vitro organic matter digestibility (IVOMD) of the bahiagrass component across treatments in year 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05)....................................................................................39 4.7. In vitro organic matter digestibility (IVOMD) of evenia leaves (leaves and stems <3 mm) in 2001. Means (bars) with different letters above them are different by PDIFF (P<0.05)........................................................................................................39 4.8. In vitro organic matter digestibility (IVOMD) of creeping vigna in 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05)...............40 ix

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science SEASONAL CHANGES IN THE HERBAGE MASS AND QUALITY OF LEGUME-BAHIAGRASS PASTURES By Maria Yolanda Castelo Ipiales December 2003 Chair: Martin B. Adjei Cochair: Carrol G. Chambliss Major Department: Agronomy Animal production in the tropical and subtropical regions is dependent on pastures. Low average daily gains (ADG) by cattle on permanent grass pastures during the summer may be overcome with protein supplementation or by including legumes in the pasture system. Florida has 1 million hectares of bahiagrass (Paspalum notatum Flugge), a warm-season perennial grass. Aeschynomene evenia (Aeschynomene evenia C. Wright) is a prolific summer, short-lived, perennial with good persistence from seedling recruitment. Shaw creeping vigna (Vigna parkeri Baker) is a summer perennial legume that has been persistent in pastures at Ona, FL. The purpose of this work was to 1) measure herbage mass and nutritive value and 2) to determine comparative growth responses of yearling cattle to variably stocked, continuously grazed evenia-bahiagrass, creeping vigna-bahiagrass, and pure bahiagrass pastures. Yearling steers were variably stocked based on herbage allowance; were placed on evenia-bahiagrass and pure bahiagrass pastures from September to December 2001; and on evenia-bahiagrass, x

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creeping vigna-bahiagrass, and pure bahiagrass pastures from May to November 2002. The contribution of evenia to the total herbage mass in 2001 was 11%. Herbage mass (HM), in vitro organic matter digestibility (IVOMD), and crude protein (CP) of bahiagrass were not different between pastures in 2001 but changed through time, 4000 to 3350 kg haHM, 70 to 61 g kgfor CP, and 409 to 307 g kgfor IVOMD. Evenia leaves had greater nutritive value than stems. Crude protein of evenia stems (86 to 58 g kg-) and leaves decreased as the season progressed (190 to 160 g kg-). The IVOMD of evenia leaves and stems did not change over time, averaging 545 g kgand 240 g kg-. In 2002, the contribution of evenia and creeping vigna to total HM was 4 and 6%, respectively. Herbage mass, CP, and IVOMD of bahiagrass in 2002 were not different among pasture systems averaging 2620 kg ha-, 77 g kg-, and 404 g kgrespectively; but did change over time, increasing from 1710 to 3310 kg hafor HM, and decreasing CP from 91 to 69 g kg-, and IVOMD increasing from 307 to 409 g kg-. The CP of creeping vigna and evenia were not different over time in 2002, averaging 193 and 162 g kgrespectively. The IVOMD of creeping vigna plants increased during the season from 631 to 726 g kgand the IVOMD of evenia plants remained the same throughout the season, with a mean of 537 g kg-. In 2001, the seasonal ADG and gain per hectare of steers (320 kg) over an 86-d period were not different (P<0.05) between evenia-bahiagrass (0.09 kg dand 9 kg ha-), and pure bahiagrass (0.16 kg dand 15 kg ha-). In 2002, seasonal ADG and gain per hectare of steers (230 kg) over a 168-d period were not different (P<0.05) among evenia-bahiagrass (0.09 kg dand 21.5 kg ha-), creeping vigna-bahiagrass (-0.04 kg dand -7.5 kg ha-), and pure bahiagrass (-0.01 kg dand -1.5 kg ha-). xi

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CHAPTER 1 INTRODUCTION The major use of tropical grasslands throughout the world is for the production of domestic livestock. Forages contribute more than 90% of the feed energy consumed by herbivorous livestock worldwide. Animal production in tropical and subtropical regions is dependent on pastures (i.e., upon the quality and quantity of forage available throughout the year). In Floridas beef industry, managers are concerned with calf weaning weight, heifer development, and cow condition at breeding. The tropical perennial grasses used as summer pastures in Florida (e.g., bahiagrass and bermudagrass) do not always have adequate nutrient composition to meet the needs of grazing animals. These grasses are often high in fiber, especially when mature, and high-producing cattle are unable to consume them in adequate quantities to meet their requirements for crude protein (CP) and total digestible nutrients (TDN) (Moore et al., 1991). Low average daily gain by cattle on permanent grass pastures during the summer may be overcome with protein supplementation or by inclusion of legume in the pastures. Legumes are valuable components in forage mixtures. Some of their contributions are ability to fix atmospheric N (which decreases the dependence on fertilizer N); increasing the protein and digestibility of the diet grazed by animals; and extending the grazing season. However, a major difficulty in promoting grass-legume mixtures in the tropics has been identifying legumes that are adapted to the prevailing environmental conditions, 1

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compatible with aggressive grass species, and able to withstand heavy grazing (Ibrahim and Mannetje 1998). Bahiagrass (Paspalum notatum Flgge) is a warm-season perennial grass, native to South America, that was introduced into the USA in 1913 by the Florida Agricultural Experimental Station (Scott, 1920). It is grown throughout Florida and in the Coastal Plain and Gulf Coast regions of the southern USA. Florida has 1 million hectares of bahiagrass. Forage quality of most warm-season perennial grasses, especially Pensacola bahiagrass usually decreases during the summer rainy season from June through September (Mislevy and Martin 2001). Aeschynomene evenia (Aeschynomene evenia C. Wright) is a prolific summer, short-lived, perennial legume adapted to moist sites throughout Florida with good persistence from seedling recruitment. Kretschmer et al. (1994) summarized research findings regarding this legume. Data indicate that evenia is water tolerant and produces seed and green foliage throughout the year, barring frost. When no frost occurs, plants overwinter and initiate regrowth from basal buds the next spring. Shaw creeping vigna (Vigna parkeri Baker cv. Shaw) is a summer perennial legume native to higher elevation and better-watered grassland areas of equatorial East Africa. It was introduced into Australia in 1954, but did not gain much recognition there until 1975 when it was noticed that earlier-sown test plots had spread into pastures. The Australians tested and released the cultivar known as Shaw. Dr. Buddy Pitman, who did all of the early evaluation work at Ona, planted Shaw at the Range Cattle REC in 1981. Of 19 legumes tested in that first study, Shaw was the most persistent under grazing in a mixture with bahiagrass (Kalmbacher and Adjei, 2001). 2

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Thus, potential may exist to integrate evenia or creeping vigna into Florida pastures. The purpose of this work was to evaluate livestock performance on, and describe forage attributes of mixtures of, these two legumes with bahiagrass. The specific objectives of this research were to 1) determine comparative growth response of yearling cattle to continuously stocked evenia-bahiagrass, Shaw creeping vigna-bahiagrass, and pure bahiagrass pastures; and 2) measure the forage nutritive value of these pastures. 3

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CHAPTER 2 LITERATURE REVIEW Characterization of Species Bahiagrass (Paspalum notatum Flgge) Bahiagrass is native to South Brazil, Uruguay, the Chaco region of North Argentina, and northwestern Paraguay (Quarin et al., 1984; Tischler et al., 1990). The common bahiagrass was introduced to the USA from Brazil in 1913 by the Bureau of Plant Industry at the Florida Agricultural Experimental Station, Gainesville (Scott, 1920). In North America, bahiagrass can be found from southern California to eastern Texas, from southern Florida to New Jersey, and from central Tennessee to Arkansas (Chese, 1929; Watson & Burton, 1985). In Florida, 1 million hectares are planted. Bahiagrass is a thick sod-forming, deep-rooted, warm-season perennial grass (Watson and Burton 1985) that persists under frequent grazing (Adjei et al., 1989). Bahiagrass is adapted to climatic conditions throughout the state. It can be grown on well-drained sandy soil as well as the moist, poorly drained flatwoods of peninsular Florida (Chambliss and Sollenberger, 1991). According to the South American Center of Diversity, cultivars of bahiagrass are tolerant to disease, drought, frost, grazing, high pH, laterite, low pH, salt, and slope (Duke, 1978). In the southeastern USA, growth rates are highest between March and October (Chambliss, 1991). Previous research has demonstrated that bahiagrass makes 86% of its growth during the six warmest months of the year in peninsular Florida (Beaty 4

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5 et al., 1980; Mislevy and Everett, 1981). The fertilization program suggested by the University of Florida for grazed bahiagrass in central and south Florida is 55 kg of N per hectare applied each spring (Kalmbacher and Wade, 2003). The cultivar Pensacola was developed in Florida from Georgia stock, and is thought to have come from South or Central America. It is more cold tolerant, has narrow blades and smaller seeds, and is more responsive to fertilizer than common bahiagrass. Its seed germination is excellent (approximately 80%), with full stands and ground cover in 8 to 12 wk. It is adapted throughout the southeastern Coastal Plain and Florida (Duke, 1983). Like other bahiagrasess, it has a fibrous root system capable of growing to a depth of 2 meters or more (Chambliss and Sollenberger, 1991). Pensacola forms a dense, thick sod that can keep weeds out and is very disease resistant, with mole crickets (Scapteriscus sp.) and armyworms (Spodoptera sp.) being the major pest problems. When mature, Pensacola bahiagrass is extremely fibrous, unpalatable, and low in nutritive value (Jones, 1971). In North Florida, more early-season and late-season production can be obtained from the Pensacola types than from other bahiagrass cultivars (Chambliss and Sollenberger, 1991). Moore et al. (1969) have shown that Pensacola bahiagrass falls in quality as it matures. Crude protein and the digestibility of organic matter and cellulose decreased with increasing age. Bahiagrass CP at 4 wk averaged 98 g kgand at 10 wk ranged from 77 to 82 g kg-; in vitro organic matter digestibility (IVOMD) ranged from 504 to 540 g kgat 4 wk and 475 to 534 g kgat 10 wk (Arthington and Brown, 2-yr average; unpublished data).

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6 Grazing trials at the Range Cattle REC have indicated little difference in livestock performance among Pensacola, Tifton-9, and Argentine bahiagrasess. Five-year average live weight gains ranged from 218 kg hato 252 kg hafor Argentine and Pensacola, respectively (Hodges et al., 1976). Aeschynomene Evenia (Aeschynomene evenia C. Wright) Evenia is found in South America and the Caribbean. It was introduced to Florida and planted on limited acreage (Sollenberger, 2002). It is a short-lived perennial legume that will survive mild winters in south Florida. It tolerates waterlogged soil and is very competitive with bahiagrass (Kalmbacher, 1996). Evenia is day-neutral and begins to flower and set seed in July rather than in late-September as is the case for common aeschynomene (Aeschynomene americana). Thus evenia may be more reliable at reseeding than aeschynomene (Kalmbacher et al., 2002). The nutritive value of evenia is similar to common aeschynomene, but unlike common aeschynomene, it has a characteristic smell and is not immediately palatable to cattle. Cattle need time to adapt to this legume and they will only graze small plants (Chambliss and Kalmbacher, 2000). It also gets more woody than common aeschynomene. Evenia is more vigorous, more persistent, and requires less management than common aeschynomene (Pate, 2001). The growing season is from April to November and it produces more fall forage than common aeschynomene (Sollenberger, 2002). Mislevy and Martin (2001) reported that whole-plant CP of evenia was 224, 198, and 206 g kgin 30, 60, and 90-cm tall plants, respectively. The IVOMD for the same experiment was 625, 581, and 571 g kg-, respectively, when plants were clipped at a 10-cm stubble height. Kalmbacher et al. (2002) reported a range in leaf CP from 215 to 308 g kg-and stem CP of 67.9 g kg-. In vitro organic matter digestibility in leaves ranged

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7 from 329 to 505 g kgand was 274 g kgin stems. In vitro organic matter digestibility of stems did not change over time. Studies by Kretschmer et al. (1994) indicate plant populations of evenia were >50% after 5 yr of clipping. Forage nutritive value of the top 30 cm of plants averaged 265 and 671 g kgCP and IVOMD, respectively, in a space-planted nursery. Shaw Creeping Vigna (Vigna parkeri Baker) Creeping vigna is indigenous to Uganda, Kenya, and Tanzania (Verdcourt, 1970). It was introduced by N. H. Shaw from the Veterinary Farm, Entebbe, Uganda, and was registered in Canberra, Australia, on 3 Dec. 1958. The cultivar Shaw, released in 1984, is recognized as the premier summer legume for dairy pastures in coastal southern Queensland and northern New South Wales, but its widespread commercial use is constrained by seed availability (Loch, 2002). Creeping vigna is a perennial herb, with both twining and prostrate stems, the latter often developing nodal roots and forming dense mats. Creeping vignas growing points and dormant buds are protected from heavy grazing when they are grown with grasses. Pitman and Kretschmer (1984) found that close grazing provided a competitive advantage for creeping vigna since it spread considerably during the growing season through elongation of short stolons, which rooted at the nodes. Creeping vigna will grow on a range of soils, from sands to heavier, but well-drained, red clays, especially on hill slopes, and can tolerate moderately low fertility and pH if fertilized with P and Mo (Humphreys and Partridge, 1995). Creeping vigna is a promising forage legume, but problems have been encountered with stand establishment and low tolerance to water stress (ODonnell et al., 1992)

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8 No grazing trials have been conducted to generate animal performance data on creeping vigna based pastures on the far North coast of Australia. However, farmers with commercial creeping vignabased pastures report improved livestock performance. Creeping vigna contributes to pasture digestibility and protein levels in late summer and autumn, when dry matter digestibility commonly drops below 600 g kg -and protein levels fall to 70 g kg-. The Commonwealth Scientific & Industrial Research Organization (CSIRO) has measured uncorrected in vitro dry matter digestibility of creeping vigna at 650 g kg(leaf) and 550 g kg(stem). Leaf digestibility does not change greatly throughout the season (Bede, 2002). Like most legumes, creeping vigna has high nutritive value. Australian literature has reported leaf and stem CP at 250 and 120 g kg-, respectively, with TDN at 610 and 550 g kg-, respectively. A study at the Range Cattle REC by Pitman in 1981 showed that out of 19 legumes tested, creeping vigna was the most persistent under grazing in a mixture with bahiagrass (Pitman and Kretschmer, 1984). Limited and expensive seed and lack of animal performance data are the main reasons creeping vigna has not become more popular among cattlemen in Florida. Grass-Legume Mixtures In many tropical areas, N deficiency is a major limitation to pasture productivity. Tropical legumes are widespread in the American tropics, where soil N in many situations is low and provides a competitive advantage to the legumes (Pitman, 1994). A viable alternative to grass with N fertilizer is legume-grass pasture. Legume-based pastures are a good alternative for forage production. There are two major advantages compared to grasses: i) only legumes can fix significant amounts of atmospheric N and ii) legumes provide greater nutrient intake potential for ruminants thereby allowing more efficient animal production. Legumes grown with grasses have several advantages over

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9 grasses grown alone. Baylor (1974) noted that including legumes in temperate pastures usually results in increased yield, high quality, and improved seasonal distribution of forage. Legume-grass mixtures had reduced weed encroachment and erosion and led to greater stand longevity than legume or grass monocultures (Droslom and Smith, 1976). Results from Sleugh et al. (2000) suggest that including legumes with grasses can improve IVOMD, CP, neutral detergent fiber (NDF), and seasonal distribution of forage yield. The higher animal performance obtained with legumes is attributed to higher CP, digestibility, and minerals, resulting in higher intake potential (Marten, 1985). Although exceptions exist, compatible legume-grass mixtures usually yield more than any single component grown in monoculture (Roberts and Olson, 1942, Aberg et al., 1943). Alternatives to supply nutrients to cattle grazing bahiagrass in late summer include growing a legume with bahiagrass, feeding supplements, or switching to one of the specialty grasses. Burns and Standaert (1985), in an extensive review of grazing experiments in the United States, reported that steer daily gains from legume-grass were 0.14 kg dmore than from N-fertilized grass and calf daily gains were 0.15 kg d-greater on legume-grass in cow-calf experiments. Daily gains of yearling steers grazing bahiagrass without a legume averaged 0.27 kg hd -during summer but increased to 0.45 kg hdwhen grazing common aeschynomene-bahiagrass pastures (Hodges et al., 1976). However, some of the major difficulties in promoting grass-legume mixtures in the humid tropics have been identifying legumes which are adapted to the prevailing environmental conditions, are compatible with aggressive grass species, and able to withstand heavy grazing (Ibrahim and Mannetje, 1998). According to Sheaffer (1989), the risk of forage legume establishment failure is associated with small seed size and a

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10 lack of seedling vigor. Limitations in water, light, and nutrients are major constraints to legume seedling persistence. Cutting trials have shown that the erect types such as stylo (Stylosanthes guianensis), and the twining climbing types of tropical legumes, such as siratro (Macroptilium atropurpureum DC.), Desmodium intortum, and Neonotonia wightii are sensitive to the frequency and height of defoliation, and that severe defoliation can lead to rapid depletion of legume content (Jones, 1967; Whiteman, 1969). Creeping legumes such as creeping vigna are less vulnerable to grazing at high stocking rates (Bryan and Evans, 1973; Jones and Clements, 1987). The survival of some legume species and cultivars under grazing is assisted by changes in growth habit in response to defoliation. For example, creeping vigna tolerates close grazing by growing close to the ground and rooting from stolons, but twines upward around associated grasses under light grazing (Jones and Clements, 1987). Incorporating legumes into our pasture increases forage quality, increases animal performance, and reduces pasture costs per animal. Although forage legumes can require more management than grasses, their high quality can make a big difference in animal performance even if legume production is limited (Bade, 1998). Forage Quality Forages consumed by Florida livestock vary in quality due to differences in genotype, maturity, season, and management. When quality is low, forages alone may not support desired rates of animal performance (Moore and Sollenberger, 2002). Quality (energy value) of warm-season perennial grasses often just barely meets the animal's requirements, or is below requirements of the beef animal during the growing season. Crude protein levels below 70 g kgcould also limit forage intake (Milford and Minson, 1965). Typically, these grasses are highest in quality in the spring, decline from June

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11 through August, then increase to October or November and rapidly decline after a freeze (Bade, 1998). The quality of the forage in any given pasture is a function of three separate but related factors; the kinds of plants present, their stage of maturity, and the time of year. Generally, the leaves of legumes are higher in quality than the leaves of grasses; grass leaves are almost always of a higher quality than the stems of either legumes or grasses (Darrell et al., 1993). Grazing Systems A grazing system is defined as an integrated combination of animal, plant, soil, and other environmental components and the grazing method by which the system is managed to achieve specific results or goals. An inventory or estimate of how much forage is or will become available for grazing is the basis of projecting how many animals can be grazed and for how long (Vallentine, 2001). Heardy (1970) defined a number of terms as follows: the grazing season is that portion of the year during which grazing is feasible. It may be year-long or shorter depending upon environmental or other restrictions of the area to grazing livestock. Grazing period is that portion of the grazing season during which grazing takes place. Grazing Management In order to optimize the yield and quality of forage produced from pasture, they must be grazed at a frequency, intensity, timing, and duration that allow the plants to remain both healthy and continually producing large quantities of high quality green leaf material (Darrell et al., 1993).

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12 Continuous Stocking Continuous stocking is a method of livestock deployment where livestock have continuous or uninterrupted use of a unit of grazing land throughout the time period in which grazing is allowed. The disadvantage of continuous stocking is that it allows little control of the timing of grazing. Under continuous stocking, livestock should be stocked at a rate that will balance the feed requirement of the herd with the forage growth rate (Rayburn, 1992). When grazing is prescribed so that there is an adequate supply of forage available to meet or exceed the dry matter requirements of the planned number of animals, gains per animal are often equal to or greater than those obtained with the rotational stocking method. This is primarily the result of selective grazing (Emmick and Fox, 1993). An improved management strategy for increasing the harvest efficiency of pastures that are continuously stocked is to alter the number of grazing animals in response to the amount of available forage. This is generally described as a put and take or variable stocking rate style of grazing management. Although pastures that are managed using this strategy may be continuously stocked during the period of time in which grazing is allowed, the forage supply is constantly monitored and adjustments to the stocking rate made by increasing or decreasing the number of grazing animals in response to the available forage supply (Emmick and Fox, 1993). With continuous stocking, the taller more productive plant species tend to decline in productivity and abundance. With the rotational stocking method, these plants can remain productive and persistent for many years (Darrell et al., 1993).

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13 Rotational Stocking Rotational stocking is where livestock are moved between pastures during the grazing season, concentrating their feeding on one pasture for a few days and then moving to a new field that is ready to graze. The grazed paddock is allowed to rest and regrow for a suitable length of time. The time needed depends on the forage species and growing conditions (Rayburn, 1992). Rotationally stocked pastures suffer from the disadvantage of requiring greater management and they limit opportunity for animals to graze forage selectively. Research in Scotland and some other countries has shown that well managed continuous stocking of pastures can be easier to accomplish, relative to rotational grazing, and can give levels of performance in the animal that exceed those achieved with rotational or strip grazing (Buchanan-Smith and Watson, 1999). Grazing Intensity The relationship between stocking rate and live weight gain of animals has been summarized by Hart (1978). Grazing intensity (frequency and closeness of grazing) regulates the opportunity of animals to graze selectively. As grazing intensity increases due to increased stocking rate (or grazing pressure), there is less herbage available per animal, thus animals become less selective in choosing the plants and plant parts eaten in order to become satiated. Correspondingly, as stocking rate increases, the level of plant defoliation increases along with changes in sward morphology and composition (Matches et al., 1981). The optimum stocking rate will always be somewhere between that which maximizes individual animal performance and that which maximizes animal performance per hectare (Clifford, 1998). Stocking rate refers to the forage demand per unit of land area for a specified length of time (Clifford, 1998). Stocking rate is considered the most important variable in

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14 grazing management; unless it is near the proper level, regardless of other grazing practices, the objectives of grazing management will not be met (Walker, 1995). Over the short term, a heavy stocking rate may lower forage quality by removing green foliage and forcing animals to consume more dead, standing forage (Lyons and Machen, 2001). Seasonal and total forage dry matter production and nutritive value should be matched with livestock requirements. The most efficient means of matching warm-season perennial forage with livestock is by the use of a variable stocking rate (Rouquette, 1993). A number of factors include animal species, size and physiological stage, size of the pasture or ranch, and number of grazeable hectares (Lyons and Machen, 2001). Increasing stocking rates on pastures decreases quantity available for each grazing animal. This will decrease the opportunity for selectivity by the animal, and in stocker animals, decrease the average daily gain. Gain per hectare, however, is increased by heavier stocking as long as forage quantity is present (Bade, 1998). Stocking rate recommendations should be based more on potential forage intake than on numbers of animals (Lyons and Machen, 2001). Herbage Allowance Herbage allowance is defined as the amount of dry forage allowed per 100 kg animal body weight daily (Adjei et al., 1980). Herbage allowance affects the quality of the diet that the animals can select, because the animal must select its diet from among a variety of different plants and plant parts of varying quality (Clifford, 1998). Smith and Whiteman (1985), in an experiment conducted in the Solomon Islands, using rotational stocking with an allowance of only 10 kg of DM kgLW d for a 28-d period, measured a maximum live weight gain of 400 g d-. On the same natural pastures (main species present Axonopus compressus, C. pubescens, M. pudica, and Calopogonium mucunoides;

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15 minor species: P. conjugatum, D. heterophyllum, D. canum, P. phaseoloides, Synedrella nodiflora, Borreria sp., Peperomia pellucida, and Mikania s.p). in a continuously stocked grazed experiment, Watson and Whiteman (1981) found that a maximum live weight gain occurred when an allowance of up to 10 kg of DM kgLW dwas given. Grazing management involves constant evaluation of total herbage mass (HM), the period during which estimated HM will be utilized, and the stocking rate (SR) required for such utilization. The rotational stocking method is defined by a specified period of grazing (GP) alternated with a specified period of rest (RP) within a grazing cycle. Based on the GP and RP, a specific number of cycles are completed within the grazing season. The bulk of forage produced on a paddock in a rotational system is consumed during the GP and forage accumulation during the RP must depend on reserve carbohydrates and residual leaf area. The daily herbage allowance method (Adjei et al., 1980) for rotational stocking is calculated by dividing the total expected HM by the GP and expressing the result as a percentage of the animal stocking rate. The converse can be used to determine animal stocking rate (kg BW ha-) for an assigned herbage allowance and estimated total HM. For a continuous stocking method, there are no defined periods of grazing and rest and the GP is actually equal to the grazing season. To be sustainable, the system must maintain sufficient HM and herbage accumulation rate at all times to support the number of assigned grazing animals. It is conceivable to spread the total estimated HM (instantaneous HM + expected herbage accumulation) at each point in the grazing season to cover the remainder of the season when calculating stocking rate at the assigned daily herbage allowance under the continuous stocking method. Subsequent adjustments in the

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16 stocking rate are then made periodically based on the concept of spreading total HM to cover the remaining time in the grazing season. Williams and Hammond (1999) have described a continuous intensive stocking method in which stocking density was temporarily increased by 75% during periods of rapid forage accumulation and the excess forage reserved as a potential for hay production. This was done to improve animal performance by matching herbage accumulation rate with forage utilization and preventing accumulation of low quality forage. Nutritive Value Animal production is a function of the daily intake of digestible dry matter and therefore depends on both the quantity of food eaten and the digestibility of the feed (Holmes et al., 1966). Forage nutritive value is often described as chemical composition and digestibility. Deficiencies of dietary protein depress intake of dry matter. In tropical grasses, CP below 70 g kgmay depress dry matter intake (Milford and Minson, 1965). Crude protein in N-fertilized bahiagrass in April ranged from120 to 150 g kg DM, and CP of unfertilized grass ranged from 90 to 120 g kgDM (Kalmbacher and Wade, 2003). Minson (1980) stated the range for CP concentration of bahiagrass is often near the 60 to 80 g kgDM. Some legumes have a higher nutritive value than grasses that result in better animal performance. Legumes contain five times the Ca, 30 to 50% more P, and twice the Mg of grasses (Evers, 2001). Animals have certain nutritive requirements based on class, age, and expected performance (gain, milk, etc.). In general, the younger the animal or the greater the expected performance level, the greater is the requirement for forage to be of high quality (Rouquette, 1993)

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17 Digestibility declines as lignin concentration increases, but the relationship between lignin concentration and digestibility varies among species (McLeod and Minson, 1974). In tropical grasses as lignin concentration increases digestibility decreases, in legumes this relationship may be less consistent. As the pasture sward matures, tropical legumes generally have greater dry matter digestibility (DMD) and voluntary intake than the associated grass (Playne and Haydock, 1972). Legume grazing can increase daily gains of cattle during the late summer and fall period (Hodges, 1978).

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CHAPTER 3 MATERIALS AND METHODS General Description of the Experimental Area The experiment was conducted from September through December 2001 and from May through November 2002 at the Range Cattle Research and Educational Center (REC), Ona, which is part of the Institute of Food and Agricultural Sciences, University of Florida. The center is located 82 55' W and 27 26'N in south central Florida (Hardee county). Climatological data shows that the average monthly minimum temperature is 11C. Frosts are most likely to occur in December, January, and February. The 61-yr mean annual precipitation is 1362 mm. The months of June through September receive the highest rainfall, and April/May the lowest rainfall (Table 3.1). Because of this rainfall pattern, frequent and shortto long-term flooding occurs on pastures in summer and severe droughts in the spring. The soils are described as Pomona fine sand (sandy, siliceous, hyperthermic Ultic Haplaquod). Experimental Procedures Legume-grass Mixture The legume-grass mixtures selected for the experiment were evenia and creeping vigna, both with bahiagrass cv. Pensacola. Bahiagrass was selected because it is the most important pasture grass cultivated in Florida. It is drought tolerant, grazing persistent, adapted to flooded soils, and grows in mixtures with most tropical legumes. Evenia has high protein levels and is generally adapted to the moist flatwoods areas in the state. 18

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19 Creeping vigna shows persistence under grazing, high nutritional value, and compatibility with aggressive grasses such as bahiagrass. Pasture Establishment Legumes were planted into established bahiagrass pastures. For legume establishment, we used close grazing (5-cm stubble height) by cattle before and immediately after sod-seeding until legume seedlings were about 8 cm tall. Then, cattle were withdrawn from pastures, and the legume was allowed to grow and become established. Legumes were sod-seeded with a no-till seeder at 12.4 kg hafor evenia on 1 June 2001 and 5.1 kg hafor creeping vigna on 31 May 2001. Evenia was reseeded at 11.2 kg haon 29 April 2002. Legume seeds did not receive any mechanical or chemical treatment, rhizobial inoculum, or fertilizer during establishment in 2001, because some common aeschynomene normally occurs in these areas. In December 2001, soil samples were taken and analyzed. In Spring 2002, pastures were limed to pH 5.5 according to soil test recommendations and received a uniform application of 15 kg haP, and 56 kg haK (336 kg haof 0-10-20) plus micronutrients: total Ca 3.3 g kg-, S (combined) 1.00 g kg-, Chlorine-not more than 20.00 g kg-, B 0.05 g kg-, soluble Cu 0.50 g kg-, soluble Fe 0.50 g kg-, soluble Mn 0.50 g kg-, Zn 0.50 g kg-, derived from triple superphosphate, superphosphate, manganese sulfate, copper sulfate, iron sulfate, zinc sulfate, and sodium borate. No N was applied because we depended on the legumes to fix atmospheric N. Treatment and Experimental Design The treatments compared in this study were 1) evenia-bahiagrass, 2) creeping vigna-bahiagrass, and 3) pure bahiagrass. Pastures were arranged in a randomized complete block design. Each treatment was replicated twice in 2-ha pastures and the total number of experimental units was six. The replications represented the blocks. Pastures

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20 were stocked continuously at a variable SR (based on herbage allowance) with growing steers. The variables measured were HM, botanical composition and density, IVOMD, CP, tissue chemical composition (P, K, Ca, Mg, Zn, Mn, Cu and Fe), cattle average daily gain (ADG), and gain per hectare. Pasture Samples Grazing Experiment In 2001, the experimental period was from September to December (86 d). The grazing season for warm season forages is from May to November, but grazing started late due to the slow establishment of the legumes. Only the evenia-bahiagrass and pure bahiagrass pastures were sampled in 2001 because the creeping vigna pastures were not well established. In 2002, the experimental period was from May to December (168 d) and the evenia-bahiagrass, creeping vigna-bahiagrass, and pure bahiagrass pastures were sampled. Forage samples were taken from pastures in September, October, and November 2001 and in May, June, July, August, September, and October 2002. The direct method was used to estimate herbage mass. Forage from six, 0.5-m quadrats with representative herbage mass were clipped to a 2.5-cm stubble from each pasture on each sampling date with an electric sheep wool shears powered by a generator. In pastures with grass-legume mixture, legume and grass were placed in separate bags at harvest. Pastures were sampled at 28-d intervals. The samples were dried at 60 C to constant weight (48-72 h) in a forced-air oven. Herbage mass (kg DM ha-) was calculated as measures of available forage in pasture determined from the mean dry weight.

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21 In 2002, herbage accumulation (HA) was estimated by using three exclosure cages, which were installed on each pasture. Each cage was 1m in size. The cages were paired with three of the outside cage samples and moved to a new location in the pasture every 28 d after harvesting inside and outside the cages to estimate herbage accumulation. The areas selected for the placement of the cages and harvested outside of cages were paired to represent average forage mass in the pastures. Botanical Composition Botanical composition of the pastures was determined as percentage by weight from the same samples used to estimate herbage mass. Botanical composition was calculated as the summation of component herbage mass (over grazing cycles) x 100 and divided by the summation of total herbage mass. The persistence of the legume was determined by conducting vegetation analysis on the grass-legume pastures over time. Data were collected in September 2001. For the year of 2002, legume stand density in pastures was measured in May, June, July, August, and October. A 1-m quadrat was used to estimate the plant density. Eight line transects were laid evenly across each pastures on a zigzag pattern. Along each transect, the quadrat was dropped at approximately 6-m intervals to provide eight points for sampling. This gives a potential for 64 (8*8) occurrences. When the quadrat was dropped at each point, the number of evenia or creeping vigna plants inside the quadrat was counted. Chemical Composition The grass and legume components were ground to pass through a 1-mm screen in a Wiley Mill. Before grinding, evenia samples from year 2001 were separated into edible (leaves and small stems < 3 mm diameter) and non-edible sections (stems > 3 mm), because plants were big and stemmy. Evenia plants from year 2002 were not separated

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22 into edible and non-edible parts because plants were small (stems < 3 mm diameter). Analyses for IVOMD and CP were performed at the Forage Evaluation Support Laboratory of the University of Florida. The IVOMD of the grass and legume was determined by a Tilley and Terry (1963) procedure as modified by Moore and Mott (1974). The CP concentration was determinate by a micro-Kjeldahl procedure. Tissue minerals were extracted from samples using the ashing/0.3025 M HCl extraction method. Tissue P, K, Ca, Mg, Zn, Mn, Cu, Fe concentrations were determined at the Analytical Research Laboratory of the University of Florida using the Inductively Coupled Argon Plasma Spectroscopy method (Thermo Jarrell Ash ICAP 61E, Franklin, MA). Animal Performance Daily herbage allowance was used to adjust the number of animals per paddock every 28 d following HM estimation. Stocking rate (kg BW ha-) d-was calculated by dividing each herbage fraction (the herbage mass or herbage accumulation [kg DM ha-]) by the appropriate number of days that forage component would be utilized, and then divided by assigned herbage allowance (kg DM [100 kg animal BW]-d-). In 2001, the herbage allowance used was 5, 8, and 10 kg DM (100 kg animal BW) dfor the months of September, October, and November, respectively. Variable herbage allowance was used because we want to determine the desirable level to be use in subsequent years of study. The estimated HM was spread to cover the remaining period of the grazing season, because we were unsure of the growt rates of bahiagrass during this period, and we did not want to run out of forage because we want to keep animals until December, and estimated HM was spread over 90 d in September, 60 d in October and 30 d in November (Appendix Table A.11).

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23 In 2002, a constant herbage allowance of 10 kg DM (100 kg animal BW) dwas utilized. In 2002, both estimated HM and herbage accumulation were used when calculating SR. Stocking rate of the pasture was calculated as the sum of the SR for estimated HM and carrying capacity for herbage accumulation. The SR for the HM fraction, in May, June and July, was estimated on a 30-d cycle, based on the concept of continuous intensive stocking (Williams and Hammond, 1999). However, from August to October, the estimated HM was spread over the remaining grazing season, 90 d in August, 60 d in September, and 30 d in October. The SR for the herbage accumulation fraction, was calculated based on a 30-d usage of HA throughout the trial (Appendix Table A.12). Three crossbred steers (Brahman x British) and three Brangus steers were assigned as testers to each pasture in 2001 and 2002, respectively. Put-and-take animals were added and removed every 28 d as needed to maintain the assigned herbage allowance. Average tester weights at the start of the experimental period were 350 and 230 kg in 2001 and 2002, respectively. Steers were 21 and 12 mo of age in 2001 and 2002, respectively, at the start of the trials. Individual animal weights (tester and put-and-takes) were taken at 28-d intervals (no shrunk steers weights) and were used to guide the addition or removal of put and take animals from pastures based on the assigned herbage allowance. The seasonal ADG was calculated as the difference between the final and initial weight of testers divided by the days of grazing season. The cumulative ADG for each month was calculated as the difference between weight of testers at the end of a month and initial weight of testers (weight at beginning of grazing season) divided by the number of days that animals had been on the pasture up to that point.

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24 Seasonal carrying capacity was calculated using both testers and put and take animals, and it was expressed in kg of live weight per hectare per day. Animal days per hectare were determined using all animals but were adjusted for the weight of the average tester. Seasonal gain per hectare was calculated as the product of ADG and animal days per hectare. Minerals were supplemented to steers ad libitum. The mineral supplement used was FRS Mineral manufactured by Lakeland Animal Nutrition, (Lakeland, FL) with the following mineral composition: Ca max. 14 g kgmin. 12 g kg-, P min. 9 g kg-, NaCl max. 24 g kg-, min. 12 g kg-, K min. 0.20 g kg-, Mg min. 0.30 g kg-, S min. 0.20 g kg-, Co min. 50 mg kg-, Cu min. 1500 mg kg-, I min. 210 mg kg-, Mn min. 500 mg kg-, Se min. 40 mg kg-, Zn min. 3000 mg kg-, F not more than 800 mg kg-, and vitamin A (min. 180000 IU/lb). Statistical Analysis The data were analyzed using least-square analysis of variance (SAS, PROC mixed). The design was a randomized complete block design with two replicates. The model included treatment (evenia-bahiagrass, creeping vigna-bahiagrass, and pure bahiagrass), month, and replicates. Analysis of variance was used to determine treatment differences in IVOMD, CP, chemical composition, ADG, and gain ha-. The PDIFF method was used for mean separation.

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25 Table 3.1. Millimeters of rainfall by month in 2001, 2002, and 61-yr average at the Range Cattle REC. ________________________________________________________________________ Month 2001 2002 61-year average ________________________________________________________________________ Jan 9 47 57 Feb 1 158 65 Mar 161 11 81 Apr 24 65 64 May 33 33 94 Jun 269 352 215 Jul 362 281 218 Aug 257 311 205 Sep 451 139 185 Oct 61 62 80 Nov 4 120 49 Dec 12 179 50 Total 1643 1756 1362

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CHAPTER 4 RESULTS AND DISCUSSION Forage Responses Herbage Mass of Sward Components Bahiagrass In 2001, there was no treatment x month interaction for bahiagrass component HM (P>0.05, Appendix Table A.1). Mean HM of the bahiagrass component was not different between treatments, and averaged 4150 kg ha(P>0.05, Appendix Table A.1). Mean HM of bahiagrass across treatments was greater (P<0.05) in October (4900 kg ha-) than September or November (Fig. 4.1). Bahiagrass HM increased from September to October and then decreased by November. This decline in HM corresponded to decreasing day length and temperature, because bahiagrass growth decreases as days become shorter. In 2002, there was no treatment x month interaction for bahiagrass HM (P>0.05, Appendix Table A.2). Mean HM of bahiagrass was not different among treatments, and averaged 2620 kg ha(P>0.05, Appendix Table A.2) A difference (P<0.05) in bahiagrass HM among months was detected; September (3320 kg ha-) had greater HM than June (1710 kg ha-) that had the lowest HM (Fig. 4.2). This was due to heavier stocking rate in anticipation of rapid forage regrowth, but growth was slower than expected. HM of bahiagrass in 2001 showed greater values, compared with those obtained in 2002 because grazing started late in 2001 when bahiagrass had accumulated to a greater extent than in 2002. HM of bahiagrass in 2002 was low because grazing started early no 26

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27 N fertilizer was applied to the pasture, and there was little contribution of N from the legume to the pastures. Evenia In 2001, HM of evenia stems was greatest (P<0.05) in September and October (380 and 270 kg ha-, Table 4.1), than in November, as a result of forage accumulation prior to grazing. Plants were bigger and evenia tends to be stemmy and woody. Following the start of grazing, the amount of evenia stems decreased. In the first month, the leaf/stem ratio was 1:1 but as times went on the percentage of evenia leaves increased, because of plant regrowth and branching into small stems. Evenia leaf mass was not different among months and averaged 290 kg ha(P>0.05, Table 4.1). In 2002, HM of evenia did not change over time averaging 100 kg ha(P>0.05). Creeping vigna In 2001, the creeping vigna-bahiagrass pasture was not sampled because it was not well established. In 2002, HM of creeping vigna did not change over time averaging 190 g kg(P>0.05). Botanical Composition Evenia-bahiagrass In 2001, total HM of the pasture (bahiagrass 4440 kg haand evenia 540 kg ha-) was 4960 kg ha-, the contribution of bahiagrass represented 89% and evenia represented 11%. In 2002, total HM of the pasture (bahiagrass 2490 kg haand evenia 100 kg ha-) was 2590, the contribution of bahiagrass to total HM represented 96% and evenia represented 4%. In 2001, grazing started in September, so evenia was well established at the start of grazing. In 2002, grazing started in May, and evenia plants although established, were still small and it is possible that steers kept eating the small evenia

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28 plants, not allowing them to grow. Therefore the contribution of evenia to total HM in 2002 was less than 2001. Creeping vigna-bahiagrass In 2002, total HM of the pasture (bahiagrass 2850 kg haand creeping vigna 190 kg ha-) was 3040 kg ha-, the contribution of bahiagrass represented 94% and evenia represented 6%. Vigna did establish well during the second year but growth was low to the ground. Density For the year 2001, only one plant count was made in September, in the evenia-bahiagrass treatment. The density of evenia was 12 plants m-. In year 2002, legumes were counted four times during the grazing period, May, June, August, and October. Density did not change over time (P>0.05), averaging 6 evenia plants mand 13 vigna plants m-. Crude Protein Bahiagrass In 2001, CP concentration in the bahiagrass component was highest (P<0.05) in September at 70 g kgand declined with time probably as a result of accumulation of mature forage (Fig. 4.3). No treatment x month interaction was detected (P>0.05, Appendix Table A.3). Crude protein of the bahiagrass component across treatments was not different with a mean of 65 g kg(P>0.05, Appendix Table A.3). Low bahiagrass CP in the pastures resulted from no N fertilizer application and probably very little contribution of N from either evenia or creeping vigna. In 2002, there was no treatment x month interaction in CP on the bahiagrass component (P>0.05, Appendix TableA.4). Crude protein concentration of the bahiagrass

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29 component across treatments was not different with a mean of 77 g kg(P>0.05, Appendix Table A.4). Crude protein concentration in bahiagrass was greater (P<0.05) in June and July with 86 and 91 g kg(Fig. 4.4). During May, rainfall was low, so HM of bahiagrass in June and July was low, and the CP was more concentrated and that probably explains the greater CP concentrations reported in this period. These bahiagrass CP levels in this experiment fall within the range of values (77-98 g kg-) reported by Arthington and Brown (Unpublished data). Evenia In 2001, evenia plants were separated into edible (leaves and stems <3 mm) and non-edible (stems> 3 mm) parts. Crude protein concentration in the edible part of evenia plants changed (P<0.05) over time, decreasing from 190 (September) to 160 g kg(November). The non-edible part was affected by month (P<0.05) decreasing from 84 (September) to 59 g kg(November) (Fig. 4.5). Crude protein of the edible part of the legume was low compared with the CP concentration in evenia leaves reported by Kalmbacher et al. (2002; CP ranged from 215 to 308 g kg-). This was probably due to the inclusion of stems <3 mm in the edible fraction. Kalmbacher et al. (2002) reported that CP of evenia stems averaged 67.9 g kgand did not change over time. In the current study, CP of stems >3 mm was different over time, being greater at the first sampling date (September) and then declining by the end of the grazing season, as a consequence of plant maturity. In 2002, CP in evenia was not different over time averaging 162 g kg(Appendix Table A.5). Crude protein of evenia was low compared with the 215 g kgin evenia plants that were 30-cm tall (Mislevy and Martin, 2002). Evenia plants sampled were shorter than 30 cm, and they had more stems than leaves at the time, and this could be the reason why CP was lower for evenia

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30 plants than those reported in the literature. Creeping vigna In 2002, CP of creeping vigna was not different (P>0.05) over months, averaging 193 g kg(Appendix Table A.5). Australian literature has reported leaf and stem CP of creeping vigna at 250 and 120 g kgrespectively, (Bede, 2002), the average of which is similar to CP of whole creeping vigna plants in this study. In Vitro Organic Matter Digestibility Bahiagrass In 2001, an interaction between treatment and month was found (P<0.05) for the bahiagrass component IVOMD. In both treatments, IVOMD of the bahiagrass component was greatest in September and decreased progressively in November. The IVOMD of the bahiagrass component from the bahiagrass-evenia mixture was lower compared with the bahiagrass component from the bahiagrass alone pastures in September (Table 4.2). The IVOMD between treatments was not different in October with a mean of 365 g kg(P>0.05, Table 4.2) but by November the IVOMD of the bahiagrass component from the pure bahiagrass pasture treatment was lower than the bahiagrass component from the mixture. The decrease in digestibility of the bahiagrass component occurred because plants became mature, tissue became lignified with time, and the quality of the grass went down. In 2002, there was no a treatment x month interaction for the bahiagrass component IVOMD (P<0.05, Appendix Table A.6). The IVOMD of the bahiagrass component among treatments was not different averaging 404 g kg(P>0.05, Appendix Table A.6). Across treatments, IVOMD of the bahiagrass component was different (P>0.05) through time, reaching 444 g kgin July, and then as the plants became mature decreasing to 360

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31 g kgin October (Fig 4.6). Arthington and Brown (unpublished data) reported bahiagrass IVOMD values in the range of 540 to 475 g kgunder clipping frequency of 4 to 10 wk, respectively, and with N fertilizer. Evenia In 2001, IVOMD of the non-edible part of evenia was not different (P>0.05) through time, with an average mean of 240 g kg(Appendix Table A.7). The IVOMD of the edible part of the legume was greater (P<0.05), in September (561 g kg-) and then decreased by November (489 g kg-) (Fig. 4.7). The IVOMD of the edible part of evenia reported in this study was greater than that of evenia leaves (239 to 505 g kg-) as reported by Mislevy and Martin (2001). Evenia plants sampled in 2002 were not separated into edible and non-edible parts because all plants were small. Plants were analyzed as a whole. The IVOMD of evenia plants remained the same throughout the season with a mean of 537 g kg(P>0.05, Appendix Table A.8). This IVOMD was low compared with the IVOMD of 613 g kg in 30-cm high evenia plants reported by Mislevy and Martin (2001). Evenia plants analyzed for IVOMD in this study contained more stems than leaves, which explains why the results were lower than those reported in the literature. Creeping vigna In 2002, IVOMD increased from 634 g kg(June) to 726 g kg(October) (Fig. 4.8). The IVOMD reported in this study, was greater than that from Australia where uncorrected in vitro dry matter digestibility was 650 g kgin the leaf and 550 g kgin the stem (Bede, 2002).

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32 Tissue Mineral Composition Bahiagrass In 2001, the concentrations of P, Ca, K, Mg, Zn, Mn, Fe, and Cu in the bahiagrass component were not different between treatments (P>0.05, Appendix, Table A.9). Concentration changed over time (P<0.05) for most minerals. Phosphorus (2.0 g kg-) and Mg (3.9 g kg-) concentrations were not different over time, but Ca, K, Zn, Mn, Fe, and Cu concentrations varied. Calcium and Mn concentration increased from September to November, and concentrations of K and Zn decreased from September to November (Table 4.3). In 2002, mineral concentration of the bahiagrass component from the three treatments was not different (P>0.05, Appendix Table A.9). Mineral concentration in the bahiagrass component was different (P<0.05) across months, as P, Ca, K, Zn, Mn, Fe, and Cu tended to decrease as the grazing season progressed, but Mg tended to increase as the season ended (Table 4.3). Evenia In 2001, the P (3.3 g kg-), Ca (7.2 g kg-), K (15.3 g kg-), Zn (47.2 mg kg-), Mn (186.2 mg kg-) and Fe (70.8 mg kg-) concentrations in evenia leaves did not change (P>0.05, Table 4.4) throughout the season. Tissue Mg and Cu concentrations were different among months (P<0.05, Table 4.4), with a range of 2.3 to 3.8 g kgand 13.0 to 19.0 mg kg-, respectively. The concentration of both minerals tended to decrease towards the end of the season. In 2001, P (2.3 g kg-), Ca (4.4 g kg-), K (9.7 g kg-), Mg (1.3 g kg-), Zn (38.8 mg kg-), and Mn (60.3 mg kg-) concentrations in evenia stems were not different (P>0.05, Table 4.4) through the months. Iron and Cu concentrations varied (P<0.05, Table 4.4).

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33 Iron increased from 24 mg kgin September to 72.5 mg kgin November. On the other hand, Cu concentration was 23 mg kgin September, decreasing to 12.5 mg kgin November. Evenia DM samples collected from May to June 2002, were not sufficient for mineral analysis. The concentration of minerals in evenia plants was not different (P>0.05) among months. Average values for minerals were P (3.8 g kg-), Ca (5.7 g kg-), K (13.3 g kg-), Mg (2.4 g kg-), Zn (39.7 mg kg-), Mn (59.3 mg kg-), Fe (60.7 mg kg-), and Cu (10.7 mg kg-) (Appendix Table A.10). Creeping vigna There was not enough creeping vigna samples in June for mineral concentration analysis. Concentration of most minerals in creeping vigna was different among months (P<0.05, Table 4.5). Manganese (72.2 mg kg-), Mg (4.4 g kg-) and Fe (117.5 mg kg-) were not different across months but P (1.6-4.0 g kg-), Ca (7.7-12.6 g kg-), K (13.0-26.5 g kg-), Zn (27.0-51.5 mg kg-) and Cu (8.5-30.5 mg kg-) differed among months. Generally, creeping vigna sampled in May had a low concentration of the minerals. This concentration increased through July and by August concentration had started to decrease. Animal Performance In 2001, the seasonal ADG and gain per hectare of 320-kg long yearling steers over the 86-d grazing period between evenia-bahiagrass (0.09 kg dand 9 kg ha-), and pure bahiagrass (0.16 kg dand 15 kg ha-) were not different (P<0.05). In 2002, seasonal ADG and gain per hectare of 230-kg yearling steers over the 168-d grazing period were not different (P<0.05) among evenia-bahiagrass (0.09 kg dand 21.5 kg ha-), creeping vigna-bahiagrass (-0.04 kg dand -7.5 kg ha-), and pure bahiagrass (-0.01 kg dand -1.5

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34 kg ha-). Animal performance in both years was poor. Stocking rate was adjusted every month according an assigned herbage allowance in order to ensure sufficient quantity forage for animals at all times during the grazing season. We consider that the quantity of forage was not a contributing factor to low animal performance. It is likely that poor animal performance was a result of poor forage quality. Forage CP and IVOMD declined substantially toward the end of the grazing season, and the cumulative ADG also decreased. (Appendix Table A.11 and A.12). Milford and Minson (1965) reported that CP concentration below 70 g kgcould limit forage intake. In the present study, bahiagrass CP was below 70 g kg-, which might have limited forage intake and as a consequence reduced the ADG. Despite the fact that legumes provided forage of higher nutritive value, ADG was not improved compared with bahiagrass alone, because the proportion of the legume DM on pasture was low. Additionally, although nutritive value of creeping vigna was high, IVOMD was 631 to 726 g kgand CP was 193 g kg-, it was suspected that the young calves were unaccustomed to it and refused to consume adequate amounts. The ADGs reported in this study were very small compared with those obtained in a previous study by Kalmbacher (1996) who observed that ADG of steers over a 112-d period was not different between evenia-bahiagrass (0.68 kg h d-) and bahiagrass alone (0.54 kg hd-). In another study, Kalmbacher et al. (2002) reported that ADG was the same for bahiagrass alone (0.39 kg hd-) and evenia-bahiagrass (0.45 kg hd-). Thus, in both instances the inclusion of the legume did not improve ADG over pure grass, but steers gained weight in Kalmbachers study probably because animals were mature heifers. In the current study, steers were 21 months of age (350 kg BW) in 2001 and 12

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35 months of age (230 kg BW) in 2002. The steers apparently consumed forage that was mainly sub maintenance and not sufficient for weight gain towards the end of the season. 0100020003000400050006000Sept.Oct.Nov.MonthHerbage mass (kg ha) bac Figure 4.1. Monthly HM of the bahiagrass component across treatments in 2001. Means (bars) with different letters above them are different by PDIFF (P<0.05).

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36 0500100015002000250030003500MayJuneJulyAug.Sept.Oct.MonthHerbage mass (kg ha) aaabcc Figure 4.2. Monthly HM of the bahiagrass component across treatments in 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05).

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37 565860626466687072Sept.Oct.Nov.MonthCP (g kgDM) abc Figure 4.3. Mean CP of the bahiagrass component across treatments in 2001. Means (bars) with different letters above them are different by PDIFF (P<0.05).

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38 0102030405060708090100MayJuneJulyAug.Sept.Oct.MonthCP (g kgDM) bbbbaa Figure 4.4. Mean CP concentration in the bahiagrass component across treatments in 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05). 020406080100120140160180200Sept.Oct.Nov.MonthCP (g kgDM) Leaves Stemsaababb Figure 4.5. Mean CP concentration in evenia leaves and stems in 2001. Means within a plant part with a different letter above the bar are different by PDIFF (P<0.05).

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39 0100200300400500MayJuneJulyAug.Sept.Oct.MonthIVOMD (g kgOM ) abcbbc Figure 4.6. Mean in vitro organic matter digestibility (IVOMD) of the bahiagrass component across treatments in year 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05). 440460480500520540560580600Sept.Oct.Nov.MonthIVOMD (g kgOM ) aab Figure 4.7. In vitro organic matter digestibility (IVOMD) of evenia leaves (leaves and stems <3 mm) in 2001. Means (bars) with different letters above them are different by PDIFF (P<0.05).

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40 580600620640660680700720740MayJuneJulyAug.Sept.Oct.MonthIVOMD (g kgOM ) ababbaac Figure 4.8. In vitro organic matter digestibility (IVOMD) of creeping vigna in 2002. Means (bars) with different letters above them are different by PDIFF (P<0.05). Table 4.1. Monthly HM (kg ha-) of evenia stems and leaves (leaves and stems <3 mm) in year 2001. ________________________________________________________________________ Month Leaves Stems ________________________________________________________________________ Sep 290 a 380 a Oct 270 a 270 a Nov 300 a 110 b Mean 290 250 ________________________________________________________________________ Means within a column with different superscripts are different by PDIFF (P<0.05)

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41 Table 4.2. In vitro organic matter digestibility (g kg-) of the bahiagrass component for treatments and month in 2001. ________________________________________________________________________ Treatment Month Evenia-bahiagrass Bahiagrass ________________________________________________________________________ Sept. 398 B a + # 420 A a Oct. 368 A b 361 A b Nov. 317 A c 296 B c Mean 361 359 ________________________________________________________________________ + Means within a column with different lower case letters are different by PDIFF (P<0.05) # Means within a row with different upper case letters are different by PDIFF (P<0.05)

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42 Table 4.3. Monthly tissue chemical composition of the bahiagrass component in 2001 and 2002. _______________________________________________________________________ P Ca K Mg Zn Mn Fe Cu _______________________g kg-_______ ____________mg kg-________________ 2001 Sep 2.1a* 2.1b 9.2a 3.8a 23.0a 134.5b 42.5a 12.0b Oct 1.9a 2.1b 9.7a 3.9a 24.5a 144.5b 40.0a 16.0a Nov 2.0a 2.5a 5.5b 4.1a 18.5b 196.5a 56.0b 12.5b Mean 2.0 2.2 8.1 3.9 22.0 158.5 46.2 13.5 2002 May 2.6b 3.8a 14.9b 2.5c 25.5b 108.0a 53.5b 13.0b Jun 3.2a 3.7a 13.1c 2.8b 35.0a 118.5a 72.5a 20.5a Jul 2.7b 2.2c 17.0a 2.2e 26.0b 61.0b 68.0ac 4.5c Aug 2.3c 2.2c 13.7c 2.4ce 18.5c 48.5c 55.5bc 2.5d Sep 2.3c 2.2c 11.6d 2.8bd 17.5c 44.0c 47.0b 2.5d Oct 2.4c 2.5b 11.4d 3.0ad 18.0c 42.5c 44.0b 3.5c Mean 2.6 2.8 13.6 5.2 23.4 70.4 46.4 7.8 ________________________________________________________________________ Means within a column and year followed by different letters are different by PDIFF (P<0.05)

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43 Table 4.4. Tissue chemical composition of evenia leaves and stems in year 2001. ________________________________________________________________________ P Ca K Mg Zn Mn Fe Cu _______________________ g kg-____________ ________ mg kg-_______________ Leaves Sep 3.0a 9.3a 15.0a 3.8a 48.5a 213.0a 62.5a 19.0a Oct 3.5a 5.4a 16.2a 2.3b 49.5a 186.5a 63.0a 13.5b Nov 3.4a 6.9a 14.7a 2.7c 43.5a 159.0a 87.0a 13.0b Mean 3.3 7.2 15.3 2.9 47.2 186.2 70.8 15.2 Stems Sep 2.1a 4.9a 9.6a 1.3a 42.5a 59.5a 24.0b 23.0a Oct 2.4a 3.9a 10.7a 1.1a 41.0a 84.0a 39.0b 19.5a Nov 2.3a 4.5a 8.8a 1.4a 33.0a 37.5a 72.5 12.5b Mean 2.3 4.4 9.7 1.3 38.8 60.3 45.2 18.3 ________________________________________________________________________ Means within a column and plant section followed by different letters are different by PDIFF (P<0.05)

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44 Table 4.5. Tissue chemical composition of creeping vigna in year 2002 ________________________________________________________________________ Month P Ca K Mg Zn Mn Fe Cu _____________________ g kg-__________ ______________ mg kg-____________ May 1.6b 12.6a 13.0b 3.7a 27.0b 95.5a 109.5a 8.5b Jul 4.0a 10.4a 26.5a 4.9a 51.5a 90.0a 151.0a 19.0b Aug 3.8a 7.7b 22.9a 4.8a 36bc 49.5a 121.5a 18.5b Sep 3.7a 8.0b 16.8b 4.9a 40.5ac 56.0a 113.0a 30.5ab Oct 3.8a 6.8b 15.5b 3.5a 50.0a 70.0a 92.5a 17.5b Mean 3.4 9.1 18.9 4.4 41.0 72.2 117.5 18.8 _______________________________________________________________________ Means within a column followed by different lower case letters are different by PDIFF (P<0.05)

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CHAPTER 5 SUMMARY AND CONCLUSIONS A grazing trial was conducted at the Range Cattle Research and Education Center, Ona of the University of Florida, from September to December 2001 and May to November in 2002 to 1) measure forage availability and nutritive value and 2) to determine comparative growth responses of yearling cattle to variably-stocked, continuously grazed evenia-bahiagrass, Shaw creeping vigna-bahiagrass, and pure bahiagrass pastures. The variables measured were: herbage mass, in vitro organic matter digestibility (IVOMD), crude protein (CP), tissue chemical composition, average daily gain (ADG), and gain per hectare. Pasture botanical composition was also measured. From the results of this experiment, we came to the following conclusions. The contribution of legumes in both years was low. A disadvantage of legumes is their slow establishment, and in the present study this happened especially with creeping vigna that did not establish in 2001. Herbage mass of the bahiagrass component was not different between pasture treatments in 2001 (4150 kg ha-) and 2002 (2720 kg h-), but it did change during the grazing season. Herbage mass of the bahiagrass component was low in 2002 because grazing started early, which prevented early season HM accumulation. Crude protein and IVOMD of the bahiagrass component were the same for all pasture treatments. Nutritive value of the bahiagrass component changed during the grazing season. Herbage CP and IVOMD of the bahiagrass component were generally 45

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46 below the average values expected for bahiagrass because no N fertilizer was applied and legume contribution to the system was poor. Evenia leaves had a greater nutritive value than the stems and creeping vigna plants had a greater nutritive value than evenia plants. More evenia forage was produced in 2001 compare with 2002. It was suspected that animals did not eat much creeping vigna in 2002 because calves were too young and unaccustomed to it. Animal performance (seasonal ADG and gain per hectare) was not different among pasture treatments. The low animal performance was a result of the low bahiagrass quality and low content of legumes in the system. Overall, forage quality was not able to cover the nutritional needs of young steers in late season. The inclusion of a legume in bahiagrass pastures did not improve overall nutritive value of the pasture sufficiently to sustain good steer performance.

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APPENDIX Table A.1. Herbage mass (kg ha-) of the bahiagrass component for pasture treatments by month in 2001. ________________________________________________________________________ Treatments Month Evenia-bahiagrass Bahiagrass Mean ________________________________________________________________________ Sep 4300 3720 4010 Oct 4990 4810 4900 Nov 3990 3110 3550 Mean 4420 3880 4150 ________________________________________________________________________ Table A.2. Herbage mass (kg ha-) of the bahiagrass component for pasture treatments by month in 2002. ________________________________________________________________________ Treatments Month Evenia-bahiagrass Creeping vigna-bahiagrass Bahiagrass Mean ________________________________________________________________________ May 2630 3040 3290 2990 Jun 1550 1780 1810 1710 Jul 2190 2070 1820 2030 Aug 3130 3470 2840 3150 Sep 3090 3830 3030 3320 Oct 2340 2910 2380 2540 Mean 2490 2850 2530 2620 ________________________________________________________________________ 47

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48 Table A.3. Mean CP (g kg-) of the bahiagrass component for pasture treatments by month in 2001. ________________________________________________________________________ Treatments Month Evenia-bahiagrass Bahiagrass Mean ________________________________________________________________________ Sep 71 69 70 Oct 61 60 61 Nov 69 60 65 Mean 67 63 65 ________________________________________________________________________ Table A.4. Mean CP (g kg-) concentration of the bahiagrass component for pasture treatments by month in 2002. ________________________________________________________________________ Treatments Month Evenia-bahiagrass Creeping vigna-bahiagrass Bahiagrass Mean ________________________________________________________________________ May 77 69 74 73 Jun 95 76 88 86 Jul 95 79 99 91 Aug 75 75 75 75 Sep 67 64 75 69 Oct 73 65 74 71 Mean 80 71 81 77 _______________________________________________________________________

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49 Table A.5. Seasonal changes in (CP g kg-) concentration in evenia and creeping vigna plants in 2002 ________________________________________________________________________ Month Evenia Creeping vigna ________________________________________________________________________ May 198 Jun 172 140 Jul 149 253 Aug 161 196 Sep 186 173 Oct 141 198 Mean 162 193 ________________________________________________________________________ No data is reported for evenia in May 2002 because evenia was not present in samples collected.

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50 Table A.6. In vitro organic matter digestibility (g kg-) of the bahiagrass component for treatments and month in 2002. _______________________________________________________________________ Treatments Month Evenia-bahiagrass Creeping vigna-bahiagrass Bahiagrass Mean ________________________________________________________________________ May 423 389 391 401 b* Jun 388 346 402 379 c Jul 469 404 459 444 a Aug 424 408 425 419 b Sep 429 406 431 422 b Oct 385 336 359 360 c Mean 419 381 411 404 _______________________________________________________________________ Means within a column with different superscripts are different by PDIFF (P<0.05) Table A.7. In vitro organic matter digestibility (g kg-) of evenia stems (> 3 mm) in 2001. _______________________________________________________________________ Month Stems _________________________________________________________________ Sep 277 Oct 218 Nov 226 Mean 240 ________________________________________________________________________

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51 Table A.8. Seasonal changes on IVOMD (g kg-) of evenia and creeping vigna plants in 2002. ________________________________________________________________________ Month Evenia Creeping vigna ________________________________________________________________________ May ---700 June 577 631 July 481 667 Aug. 465 657 Sept. 598 688 Oct. 563 726 Mean 537 678

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52 Table A.9. Tissue chemical composition of the bahiagrass component for treatments in 2001 and 2002. ________________________________________________________________________ P Ca K Mg Zn Mn Fe Cu ______________________________g kg__________ _________mg kg-_________ 2001 Evenia-bahiagrass 2.1 2.3 8.6 3.9 22.0 128.5 123.0 12.5 Bahiagrass 1.9 2.2 7.7 4.0 21.5 159.0 45.5 14.5 Mean 2.0 2.3 8.2 3.9 21.8 158.8 84.2 13.5 2002 Evenia-bahiagrass 2.7 2.7 13.9 2.6 24.5 72.0 55.5 8.0 Creeping vigna2.3 2.8 13.3 2.5 21.5 65.5 60.5 7.0 bahiagrass Bahiagrass 2.7 2.8 13.6 2.6 24.5 74.5 54.0 8.0 Mean 2.6 2.8 13.6 2.6 23.5 70.7 56.7 7.7 ________________________________________________________________________ Table A.10. Tissue chemical composition of evenia in 2002. ________________________________________________________________________ Month P Ca K Mg Zn Mn Fe Cu ________________________g kg-______ ___________mg kg-_________________ Aug 3.5 5.0 14.5 1.9 36.5 44.5 57.5 11.0 Sep 4.0 7.1 14.4 3.2 45.0 84.5 80.0 10.5 Oct 3.8 5.1 11.0 2.1 37.5 49.0 44.5 10.5 Mean 3.8 5.7 13.3 2.4 39.7 56.7 61.7 10.7 ______________________________________________________________________

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Table A.11. Monthly HM, SR, and cumulative ADG with a variable herbage allowance in 2001. ____________________________________________________________________________________________________________ Month HM Herbage allowance Calculated SR Applied SR Cumulative ADG kg hakg DM (100 kg BW ha)dkg BW hakg BW hakg d____________________________________________________________________________________________________________ Sept. Evenia-bahiagrass 4580 5 1020 910 0.84 Bahiagrass 3720 5 830 780 0.82 Oct. Evenia-bahiagrass 5270 8 1090 1000 0.53 53 Bahiagrass 4820 8 1000 930 0.47 Nov. Evenia-bahiagrass 3980 10 1327 1010 0.09 Bahiagrass 3120 10 1040 935 0.16 ____________________________________________________________________________________________________________

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Table A.12. Monthly total HM, herbage accumulation (HA), SR, and cumulative ADG with a constant herbage allowance of 10 kg DM (100 kg BW) dfor evenia-bahiagrass (EB), creeping vigna-bahiagrass (CVB) and pure bahiagrass (B) pastures in 2002. ____________________________________________________________________________________________________________ Month HM SR for HM HA SR for HA Calculated SR Applied SR Cumulative ADG kg hakg BW hakg hakg BW hakg BW hakg BW hakg d____________________________________________________________________________________________________________ May EB 2630 880 / / 880 700 0.51 CVB 3040 1013 / / 1013 775 0.64 B 3290 1100 / / 1100 880 0.67 June EB 1550 517 712 237 755 750 0.42 54 CVB 1780 593 372 124 717 840 0.37 B 1810 603 712 104 707 880 0.45 July EB 2190 730 970 325 1055 700 0.31 CVB 2100 700 930 310 1010 620 0.21 B 1820 605 810 270 880 620 0.28 ____________________________________________________________________________________________________________ No HM data reported since grazing season started in May and no herbage accumulation data was available at that time.

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55 Table A.12. continued ____________________________________________________________________________________________________________ Month HM SR for HM HA SR for HA Calculated SR Applied SR Cumulative ADG kg hakg BW hakg hakg BW hakg BW hakg BW hakg d___________________________________________________________________________________________________________ Aug. EB 3130 350 1710 570 920 700 0.21 CVB 3480 390 970 325 710 620 0.16 B 2840 320 1380 460 780 620 0.12 Sept. EB 3090 515 1340 450 960 825 0.12 CVB 3830 640 1020 340 980 685 0.04 B 3030 505 880 295 800 660 0.03 Oct. EB 2340 780 240 80 860 800 0.09 CVB 2910 970 20 7 980 660 -0.04 B 2380 795 340 115 905 630 -0.10 __________________________________________________________________________________________________________

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58 Humphreys, L.R., and I.J. Partridge. 1995. A guide to better pastures for the tropics and subtropics. NSW Agriculture. Ibrahim, M.A., and L. Mannetje. 1998. Compatibility, persistence and productivity of grass-legume mixtures in the humid tropics of Costa Rica. Tropical Grassland. 32: 96-104. Jones, D.W. 1971. Bahiagrass in Florida. Cooperative Extension Service Institute of Food and Agricultural Sciences, Univ. Fla. Circular 321A. Jones, R.J. 1967. The effects of some grazed tropical grass-legume mixtures and nitrogen fertilized grass on total soil nitrogen, organic carbon and subsequent yields of Sorghum vulgare. Aust. J. Exp. Agric. Anim. Husb. 7:66-71. Jones, R.M., and R.J. Clements. 1987. Persistence and productivity of Centrosema virginianum and Vigna parkerri cv. Shaw under grazing on the coastal lowlands of South-east Queensland. Trop. Grassl. 21:55-64. Kalmbacher, R.S. 1996. Aeschynomene evenia. The Florida Cattleman and Livestock Journal. 61:9. Kalmbacher, R.S., and M. Adjei. 2001. Shaw Creeping Vigna. The Florida Cattleman and Livestock Journal. 66:1. Kalmbacher, R. S., and M. Wade. 2003. Value of spring fertilization of bahiagrass. University of Florida, Gainesville. http://edis.ifas.ufl.edu July 2003. Kalmbacher, R.S., F.M. Pate, and F.G. Martin. 2002. Grazing evaluation of bahiagrass with evenia aeschynomene and stylosanthes. Soil Crop Sci. Soc. Florida Proc. 61:10-15. Kretschmer, A.E., Jr. W.D. Pitman, R.C. Bullock, and T.C. Willson. 1994. Aeschynomene evenia. C Wright (Aeschynomene evenia), a perennial legume for grazing in South Florida. Soil and Crop Sci. Soc. Fla. Proc. 53:52-59. Loch, D.S. 2002. Seed production of Creeping vigna. http://www.rirde.gov.au/comp01/pasture1.html#HS-1A Lyons, R.K., and R.V. Machen. 2001. Stocking rate: the key grazing management decision. Texas Agricultural Extension Service. The Texas A&M University System. L-54006-01. Marten, G.C. 1985. Nutritional value of the legume in temperate pastures of the United States. p. 204-212. In R. F. Barnes et al. (ed.) Forage legumes for energy efficient animal production. Proc. Trilateral Workshop, Palmerston North, NZ., 30 Apr.-4 May 1984. USDA, Washington, DC.

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59 Matches, A.G., F.A. Martz, D.A. Sleper, and M.T. Krysowaty. 1981. Selecting levels of herbage allowance to compare forages for animal performance. p. 331-339. In J.L. Wheeler and R. D. Mochrie (ed.) Forage evaluation: Concepts and techniques. CSIRO, Melbourne. McLeod, M.N., and D.J. Minson. 1974. The accuracy of predicting dry matter digestibility of grasses from lignin analysis by three different methods. J. Sci. Fd Agric. 25: 907-911. Milford, R., and D.J. Minson. 1965. Intake of tropical pasture species. Proc. IX Int. Grassl. Cong., Sao Paulo, Brazil pp 815-822. Mislevy, P., and P.H. Everett. 1981. Subtropical grass species response to different irrigation and harvest regimes. Agron. J. 73:601-604. Mislevy, P., and F.G. Martin. 2001. Harvest management of evenia aeschynomene. Soil Crop Sci. Soc. Fla. Proc. 60:120-124. Minson, D.J. 1980. Nutritional differences between tropical and temperature pastures. p. 143-157. In F.H.W. Morley (ed.). Grazing animals. Elsevier Scientific Publishing Co., Amsterdam, Holland. Moore, J.E., G.L. Ellis, C.E. Rios, and M. Koger. 1969. Estimates of the voluntary intake and nutrient digestibility of bahiagrass pasture by grazing steers. Soil and Crop Sci. Soc. Fla. Proc. 29:168-175. Moore, J.E., W.E. Kunkle, and W.F. Brown. 1991. Forage quality and the needs for protein and energy supplements. p. 11-123. In Proceedings of the Beef Cattle Short Course, Animal Science Department, University of Florida, Gainesville, Florida. Moore, J.E. and L.E. Sollenberger. 2002. Forage Quality. University of Florida. Cooperative Extension Service. SS-AGR-93. O'Donnell, D.M., J.J. Sylvia, J.E. Rechcigl, and W.D. Pitman. 1992. Inoculation of Vigna parkeri with mycorrhizal fungi in an acid Florida spodosol. Tropical Grasslands 26:120-129. Pate, F. 2001. Planting summer legumes in bahiagrass pastures. Peace River Farmer and Rancher. 4:8. Pitman, W.D. 1994. Tropical pasture development. Encyclopedia of Agricultural Science. 4:395-403. Pitman, W.D., and A.E. Kretschmer, Jr. 1984. Persistence of selected tropical pasture legumes in peninsular Florida. Agron. J. 76:993-996.

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60 Playne, M.J., and K.P Haydock. 1972. Nutritional value of Townsville stylo (Stylosanthes humilis) and of spear grass (Heterocarpon contortus)dominant pastures fed to sheep. 1. Effects of plant maturity. Aust. J. Exp. Agric. Anim. Husb. 12: 365-372. Quarin, C.L., B.L. Burton, and G.W. Burton. 1984. Cytology of intra and interspecific hybrids between two cytotypes of Paspalum notatum and P. cromyorrhizon. Bot. Gaz. 145:420-426. Rayburn, E.B. 1992. Grazing systems. West Virginia University, Extension Service. http://www.caf.wvu.edu/~forage/5712.htm January 2002. Roberts, J.L., and F.R. Olson. 1942. Interrelationships of grass and legumes grown in association. Agron. J. 34:695-701. Rouquette, F.M. 1993. Grazing management systems for optimum pasture utilization. p 103 In 42nd Annual Florida Beef Cattle Short Course Proceedings; 57 May 1993; Gainesville, FL. University of Florida (Gainesville): Animal Science Department. Scott, J.M. 1920. Bahiagrass. University of Florida Agricultural Experiment Station, Gainesville, FL. Sheaffer, C.C. 1989. Legume establishment and harvest management in the USA. p. 277-291. In G.C. Marten et al. (ed.) Persistence of forage legumes. ASA. CSSA, and SSSA. Madison, WI. Sleugh B., K.J. Moore, R.J. George, and E.C. Brummer. 2000. Binary legume-grass mixtures improve forage yield, quality and seasonal distribution. Agron. J. 92:24-29. Smith, M.A., and P.C. Whiteman. 1985. Animal production from rotationally-grazed natural and sown pastures under coconuts at three stocking rates in the Solomon Islands. J. Agric. Sci. (Cambridge) 104:173-180. Sollenberger, L.E. 2002. Forage Science and range management lab outlines. AGR 4231. The Florida Book Store Custom Publishing Department. University of Florida. Gainesville, FL. Tischler, C.R., P.W. Voigt, and B. L. Burton. 1990. Evaluation of Paspalum germoplasm, for variation in leaf wax and heat tolerance. Euphytica 50:73-79. Vallentine, J.F. 2001. Grazing management. Second Edition. Academic Press. San Diego, California. Verdcourt, B. 1970. Studies in the leguminosae-Papilionoideae for the flora of tropical East Africa: IV. Kew Bulletin 24:507-569. Walker, J.W. 1995. Grazing management and research now and in the next millennium: A viewpoint. J. Range Mgt. 48:350-357.

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61 Watson S.E., and Whiteman P.C. 1981. Grazing studies on the Guadalcanal Plains, Solomon Islands 2. Effects of pasture mixtures and stocking rate on animal production and pasture components. J. Agric. Sci. (Cambridge) 97:353-364. Watson, V.H., and B.L. Burton. 1985. Bahiagrass, carpetgrass and dallisgrass. p. 225-233. Forages: The Science of Grassland Agriculture. Iowa State University Press, Ames, IA. Whiteman, P.C. 1969. The effects of close grazing and cutting on the yield, persistence and nitrogen content of four tropical legumes with Rhodes grass at Stamford, South-Eastern Queensland. Aust. J. Exp. Agric. Anim. Husb. 9:287-294. Williams, M.J., and A.C. Hammond. 1999. Rotational vs. continuous intensive stocking management of bahiagrass pasture for cows and calves. Agron. J. 91:11-16.

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BIOGRAPHICAL SKETCH Maria Yolanda Castelo Ipiales was born September 12, 1976 in Quito, Pichincha province, Ecuador. She graduated from Colegio Frances High School, Quito, Ecuador in 1994. From January 1995 to May 1999, she attended the Escuela Agricola Panamericana, El Zamorano, in Honduras; and received the Ingeniero Agronomo degree with a major in plant protection. From January 2000 to June 2001 she participated in the Minnesota Agricultural Student Trainee (MAST) program from the University of Minnesota. She entered graduate school at the University of Florida in August 2001. She is a candidate for the Master of Science degree, with a major in agronomy and a minor in agricultural education and communication. 62


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Title: Seasonal Changes in the Herbage Mass and Quality of Legume-Bahiagrass Pastures
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SEASONAL CHANGES IN HERBAGE MASS AND QUALITY OF
LEGUME-BAHIAGRASS PASTURES















By

MARIA YOLANDA CASTELO IPIALES


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA
2003

































Copyright 2003

By

Maria Yolanda Castelo Ipiales


































Dedicated to my husband, Jose Luis; my father, Teofilo, and my mother, Aida.















ACKNOWLEDGMENTS

The author wishes to express her sincere thanks and appreciation to Dr. Martin

Adjei (chair of her supervisory committee) for all his help and guidance throughout the

fieldwork and graduate program. Appreciation is also extended to Drs. Carrol Chambliss,

Lynn Sollenberger, John Arthington, and Nick Place (members of the supervisory

committee) for their advice. The author acknowledges the help given to her during the

research by the personnel at the Range Cattle REC in Ona, Florida.

Special acknowledgement is due to the author's husband, Jose Luis, for his

invaluable help and love. Finally, sincere appreciation is extended to the author's family

for their understanding and encouragement.
















TABLE OF CONTENTS
page

A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES ....................................................... ............ .............. .. vii

LIST OF FIGURES ......... ............................... ........ ............ ix

A B ST R A C T .......... ..... ...................................................................................... x

CHAPTER

1 IN TRODU CTION ................................................. ...... .................

2 LITER A TU R E REV IEW ............................................................. ....................... 4

C haracterization of Species ........................................ .................. .. ............... 4
Bahiagrass (Paspalum notatum Flugge) ...............................................................4
Aeschynomene Evenia (Aeschynomene evenia C. Wright)............... ...............6
Shaw Creeping Vigna (Vignaparkeri Baker) .............. ...................... ...........7
G rass-L egum e M ixtures ............................................................... ....................... 8
F orag e Q u ality ................................................................10
Grazing Systems ................. ..... .................................11
Grazing M anagem ent ........... ........... ......... .................................. 11
C ontinuou s Stocking .................................................... ........ .................12
R otational Stocking .......... ........................... ........ ...... .. ........ .... 13
Grazing Intensity .................................. .. .. ...... ........... ... 13
H erbage A llow ance ........................ .. ....................... ...... .. .......... 14
N u tritiv e V a lu e ..................................................................................................... 1 6

3 M ATERIALS AND M ETHOD S ........................................ ......................... 18

General Description of the Experimental Area .......................................................18
Experim ental Procedures ...................................................................................... 18
L egu m e-grass M ixtu re............................................ ....................................... 18
P asture E stablishm ent........ .................................................. ...... ............. 19
Treatment and Experimental Design..... .......... ........................................ 19
Pasture Sam ples ................................................................... ........... 20
G razing Experim ent ............................................... .... .... .. ............ 20
B otanical C om position .............................................. .............................. 21
Chem ical Com position ......................................................... ............... 21


v









A nim al P perform an ce ............................................................................. .. ......22
Statistical Analysis............... ....................... ......... 24

4 RESULTS AND DISCU SSION ........................................... .......................... 26

Forage Responses .................. ....... ............... ...............26
Herbage M ass of Sward Components ...................................... ............... 26
B ah iag ra ss ..............................................................2 6
E venia................................................... 27
C reep in g v ig n a .............................. ........................ .. ........ .... ............2 7
B otanical C om position ............................................... ............................. 27
Evenia-bahiagrass .......... ..... ................................................. 27
Creeping vigna-bahiagrass ........................................ ........ ............... 28
D e n sity ................................................................................................... 2 8
C ru d e P ro te in ................................................................................................. 2 8
B ah iag ra ss ..............................................................2 8
E venia................................................... 29
Creeping vigna ............................................. ........30
In V itro Organic M atter D igestibility ................................................................30
B ah iag ra ss ..............................................................3 0
E venia................................................... 3 1
Creeping vigna ................................. ............................ .......31
Tissue M ineral C om position ....................................................... 32
B ah iag ra ss ..............................................................3 2
E venia................................................... 32
C re ep in g v ig n a ....................................................................................... 3 3
A n im al P perform an ce ............................................................................................. 3 3

5 SUMMARY AND CONCLUSIONS .............................................................. 45

A P P E N D IX ......................................................................................................4 7

L IST O F R E FE R E N C E S ............................................................................... 56

B IO G R A PH IC A L SK E T C H ....................................................................................... 62















LIST OF TABLES


Tablege

3.1. Millimeters of rainfall by month in 2001, 2002, and 61-yr average at the Range
C battle R E C ..........................................................................2 5

4.1. Monthly HM (kg ha-) of evenia stems and leaves (leaves and stems <3 mm)
in year 2001 ..................................... ................................. .......... 40

4.2. In vitro organic matter digestibility (g kg-') of the bahiagrass component for
treatm ents and m onth in 2001............................................................................. ..41

4.3. Monthly tissue chemical composition of the bahiagrass component in 2001 and
2 0 02 .................................................................................4 2

4.4. Tissue chemical composition of evenia leaves and stems in year 2001 .................43

4.5. Tissue chemical composition of creeping vigna in year 2002 ..............................44

A. 1. Herbage mass (kg ha-) of the bahiagrass component for pasture treatments by
m month in 2001 .................................... ............................... .......... 47

A.2. Herbage mass (kg ha-') of the bahiagrass component for pasture treatments by
m onth in 2002 ................................................... ................. 47

A.3. Mean CP (g kg-') of the bahiagrass component for pasture treatments by
m month in 2001 .................................... ............................... .......... 48

A.4. Mean CP (g kg-) concentration of the bahiagrass component for pasture
treatm ents by m onth in 2002 .................................. ............... ............... 48

A.5. Seasonal changes in (CP g kg-) concentration in evenia and creeping vigna
p lan ts in 2 0 0 2 ...................................................................... 4 9

A.6. In vitro organic matter digestibility (g kg-') of the bahiagrass component for
treatm ents and m onth in 2002. ............................................................................ 50

A.7. In vitro organic matter digestibility (g kg-') of evenia stems (> 3 mm) in 2001......50

A.8. Seasonal changes on IVOMD (g kg-') of evenia and creeping vigna plants
in 2002 .............. ..... ........ ......................... ....... .................. 51









A.9. Tissue chemical composition of the bahiagrass component for treatments
in 2001 and 2002. .......................................................................52

A. 10. Tissue chemical composition of evenia in 2002. ............. ........................ ......... 52

A. 11. Monthly HM, SR, and cumulative ADG with a variable herbage allowance
in 2001 ..................................... .................. ................ ........... 53

A. 12. Monthly total HM, herbage accumulation (HA), SR, and cumulative ADG with a
constant herbage allowance of 10 kg DM (100 kg BW) d-' for evenia-bahiagrass
(EB), creeping vigna-bahiagrass (CVB) and pure bahiagrass (B)
p astu res in 2 0 0 2 ................................................. .................. 54















LIST OF FIGURES


Figure page

4.1. Monthly HM of the bahiagrass component across treatments in 2001.Means
(bars) with different letters above them are different by PDIFF (P<0.05)...............35

4.2. Monthly HM of the bahiagrass component across treatments in 2002. Means
(bars) with different letters above them are different by PDIFF (P<0.05)...............36

4.3. Mean CP of the bahiagrass component across treatments in 2001. Means (bars)
with different letters above them are different by PDIFF (P<0.05).........................37

4.4. Mean CP concentration in the bahiagrass component across treatments in 2002.
Means (bars) with different letters above them are different by PDIFF (P<0.05)...38

4.5. Mean CP concentration in evenia leaves and stems in 2001. Means within a plant
part with a different letter above the bar are different by PDIFF (P<0.05)..............38

4.6. Mean in vitro organic matter digestibility (IVOMD) of the bahiagrass component
across treatments in year 2002. Means (bars) with different letters above them are
different by PD IFF (P<0.05). ........................................... ............................ 39

4.7. In vitro organic matter digestibility (IVOMD) of evenia leaves (leaves and stems
<3 mm) in 2001. Means (bars) with different letters above them are different by
P D IF F (P < 0 .0 5) .................................................... ................ 3 9

4.8. In vitro organic matter digestibility (IVOMD) of creeping vigna in 2002. Means
(bars) with different letters above them are different by PDIFF (P<0.05)...............40















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

SEASONAL CHANGES IN THE HERBAGE MASS AND QUALITY OF
LEGUME-BAHIAGRASS PASTURES
By

Maria Yolanda Castelo Ipiales

December 2003

Chair: Martin B. Adjei
Cochair: Carrol G. Chambliss
Major Department: Agronomy

Animal production in the tropical and subtropical regions is dependent on pastures.

Low average daily gains (ADG) by cattle on permanent grass pastures during the summer

may be overcome with protein supplementation or by including legumes in the pasture

system. Florida has 1 million hectares of bahiagrass (Paspalum notatum Flugge), a

warm-season perennial grass. Aeschynomene evenia (Aeschynomene evenia C. Wright) is

a prolific summer, short-lived, perennial with good persistence from seedling

recruitment. "Shaw" creeping vigna (Vignaparkeri Baker) is a summer perennial legume

that has been persistent in pastures at Ona, FL. The purpose of this work was to 1)

measure herbage mass and nutritive value and 2) to determine comparative growth

responses of yearling cattle to variably stocked, continuously grazed evenia-bahiagrass,

creeping vigna-bahiagrass, and pure bahiagrass pastures. Yearling steers were variably

stocked based on herbage allowance; were placed on evenia-bahiagrass and pure

bahiagrass pastures from September to December 2001; and on evenia-bahiagrass,









creeping vigna-bahiagrass, and pure bahiagrass pastures from May to November 2002.

The contribution of evenia to the total herbage mass in 2001 was 11%. Herbage mass

(HM), in vitro organic matter digestibility (IVOMD), and crude protein (CP) of

bahiagrass were not different between pastures in 2001 but changed through time, 4000

to 3350 kg ha- HM, 70 to 61 g kg-' for CP, and 409 to 307 g kg- for IVOMD. Evenia

leaves had greater nutritive value than stems. Crude protein of evenia stems (86 to 58 g

kg-') and leaves decreased as the season progressed (190 to 160 g kg-'). The IVOMD of

evenia leaves and stems did not change over time, averaging 545 g kg- and 240 g kg-'. In

2002, the contribution of evenia and creeping vigna to total HM was 4 and 6%,

respectively. Herbage mass, CP, and IVOMD of bahiagrass in 2002 were not different

among pasture systems averaging 2620 kg ha-', 77 g kg-' and 404 g kg-' respectively; but

did change over time, increasing from 1710 to 3310 kg ha-' for HM, and decreasing CP

from 91 to 69 g kg-', and IVOMD increasing from 307 to 409 g kg-'. The CP of creeping

vigna and evenia were not different over time in 2002, averaging 193 and 162 g kg-'

respectively. The IVOMD of creeping vigna plants increased during the season from 631

to 726 g kg- and the IVOMD of evenia plants remained the same throughout the season,

with a mean of 537 g kg-'. In 2001, the seasonal ADG and gain per hectare of steers (320

kg) over an 86-d period were not different (P<0.05) between evenia-bahiagrass (0.09 kg

d-' and 9 kg ha-'), and pure bahiagrass (0.16 kg d' and 15 kg ha-'). In 2002, seasonal ADG

and gain per hectare of steers (230 kg) over a 168-d period were not different (P<0.05)

among evenia-bahiagrass (0.09 kg d-' and 21.5 kg ha-'), creeping vigna-bahiagrass (-0.04

kg d- and -7.5 kg ha-'), and pure bahiagrass (-0.01 kg d-' and -1.5 kg ha-').














CHAPTER 1
INTRODUCTION

The major use of tropical grasslands throughout the world is for the production of

domestic livestock. Forages contribute more than 90% of the feed energy consumed by

herbivorous livestock worldwide. Animal production in tropical and subtropical regions

is dependent on pastures (i.e., upon the quality and quantity of forage available

throughout the year).

In Florida's beef industry, managers are concerned with calf weaning weight, heifer

development, and cow condition at breeding. The tropical perennial grasses used as

summer pastures in Florida (e.g., bahiagrass and bermudagrass) do not always have

adequate nutrient composition to meet the needs of grazing animals. These grasses are

often high in fiber, especially when mature, and high-producing cattle are unable to

consume them in adequate quantities to meet their requirements for crude protein (CP)

and total digestible nutrients (TDN) (Moore et al., 1991).

Low average daily gain by cattle on permanent grass pastures during the summer

may be overcome with protein supplementation or by inclusion of legume in the pastures.

Legumes are valuable components in forage mixtures. Some of their contributions are

ability to fix atmospheric N (which decreases the dependence on fertilizer N); increasing

the protein and digestibility of the diet grazed by animals; and extending the grazing

season. However, a major difficulty in promoting grass-legume mixtures in the tropics

has been identifying legumes that are adapted to the prevailing environmental conditions,









compatible with aggressive grass species, and able to withstand heavy grazing (Ibrahim

and Mannetje 1998).

Bahiagrass (Paspalum notatum Fliugge) is a warm-season perennial grass, native to

South America, that was introduced into the USA in 1913 by the Florida Agricultural

Experimental Station (Scott, 1920). It is grown throughout Florida and in the Coastal

Plain and Gulf Coast regions of the southern USA. Florida has 1 million hectares of

bahiagrass. Forage quality of most warm-season perennial grasses, especially 'Pensacola'

bahiagrass usually decreases during the summer rainy season from June through

September (Mislevy and Martin 2001).

Aeschynomene evenia (Aeschynomene evenia C. Wright) is a prolific summer,

short-lived, perennial legume adapted to moist sites throughout Florida with good

persistence from seedling recruitment. Kretschmer et al. (1994) summarized research

findings regarding this legume. Data indicate that evenia is water tolerant and produces

seed and green foliage throughout the year, barring frost. When no frost occurs, plants

overwinter and initiate regrowth from basal buds the next spring.

Shaw creeping vigna (Vignaparkeri Baker cv. Shaw) is a summer perennial

legume native to higher elevation and better-watered grassland areas of equatorial East

Africa. It was introduced into Australia in 1954, but did not gain much recognition there

until 1975 when it was noticed that earlier-sown test plots had spread into pastures. The

Australians tested and released the cultivar known as Shaw. Dr. Buddy Pitman, who did

all of the early evaluation work at Ona, planted Shaw at the Range Cattle REC in 1981.

Of 19 legumes tested in that first study, Shaw was the most persistent under grazing in a

mixture with bahiagrass (Kalmbacher and Adjei, 2001).









Thus, potential may exist to integrate evenia or creeping vigna into Florida

pastures. The purpose of this work was to evaluate livestock performance on, and

describe forage attributes of mixtures of, these two legumes with bahiagrass.

The specific objectives of this research were to 1) determine comparative growth

response of yearling cattle to continuously stocked evenia-bahiagrass, Shaw creeping

vigna-bahiagrass, and pure bahiagrass pastures; and 2) measure the forage nutritive value

of these pastures.
















CHAPTER 2
LITERATURE REVIEW

Characterization of Species

Bahiagrass (Paspalum notatum Fliigge)

Bahiagrass is native to South Brazil, Uruguay, the Chaco region of North

Argentina, and northwestern Paraguay (Quarin et al., 1984; Tischler et al., 1990). The

common bahiagrass was introduced to the USA from Brazil in 1913 by the Bureau of

Plant Industry at the Florida Agricultural Experimental Station, Gainesville (Scott, 1920).

In North America, bahiagrass can be found from southern California to eastern Texas,

from southern Florida to New Jersey, and from central Tennessee to Arkansas (Chese,

1929; Watson & Burton, 1985). In Florida, 1 million hectares are planted. Bahiagrass is a

thick sod-forming, deep-rooted, warm-season perennial grass (Watson and Burton 1985)

that persists under frequent grazing (Adjei et al., 1989). Bahiagrass is adapted to climatic

conditions throughout the state. It can be grown on well-drained sandy soil as well as the

moist, poorly drained flatwoods of peninsular Florida (Chambliss and Sollenberger,

1991).

According to the South American Center of Diversity, cultivars of bahiagrass are

tolerant to disease, drought, frost, grazing, high pH, laterite, low pH, salt, and slope

(Duke, 1978). In the southeastern USA, growth rates are highest between March and

October (Chambliss, 1991). Previous research has demonstrated that bahiagrass makes

86% of its growth during the six warmest months of the year in peninsular Florida (Beaty









et al., 1980; Mislevy and Everett, 1981). The fertilization program suggested by the

University of Florida for grazed bahiagrass in central and south Florida is 55 kg of N per

hectare applied each spring (Kalmbacher and Wade, 2003).

The cultivar 'Pensacola' was developed in Florida from Georgia stock, and is

thought to have come from South or Central America. It is more cold tolerant, has narrow

blades and smaller seeds, and is more responsive to fertilizer than common bahiagrass. Its

seed germination is excellent (approximately 80%), with full stands and ground cover in

8 to 12 wk. It is adapted throughout the southeastern Coastal Plain and Florida (Duke,

1983). Like other bahiagrasess, it has a fibrous root system capable of growing to a depth

of 2 meters or more (Chambliss and Sollenberger, 1991). Pensacola forms a dense, thick

sod that can keep weeds out and is very disease resistant, with mole crickets

(Scapteriscus sp.) and armyworms (Spodoptera sp.) being the major pest problems.

When mature, Pensacola bahiagrass is extremely fibrous, unpalatable, and low in

nutritive value (Jones, 1971). In North Florida, more early-season and late-season

production can be obtained from the Pensacola types than from other bahiagrass cultivars

(Chambliss and Sollenberger, 1991).

Moore et al. (1969) have shown that Pensacola bahiagrass falls in quality as it

matures. Crude protein and the digestibility of organic matter and cellulose decreased

with increasing age. Bahiagrass CP at 4 wk averaged 98 g kg-1 and at 10 wk ranged from

77 to 82 g kg-1; in vitro organic matter digestibility (IVOMD) ranged from 504 to 540 g

kg-1 at 4 wk and 475 to 534 g kg-1 at 10 wk (Arthington and Brown, 2-yr average;

unpublished data).









Grazing trials at the Range Cattle REC have indicated little difference in livestock

performance among Pensacola, Tifton-9, and Argentine bahiagrasess. Five-year average

live weight gains ranged from 218 kg ha-1 to 252 kg ha-1 for Argentine and Pensacola,

respectively (Hodges et al., 1976).

Aeschynomene Evenia (Aeschynomene evenia C. Wright)

Evenia is found in South America and the Caribbean. It was introduced to Florida

and planted on limited acreage (Sollenberger, 2002). It is a short-lived perennial legume

that will survive mild winters in south Florida. It tolerates waterlogged soil and is very

competitive with bahiagrass (Kalmbacher, 1996). Evenia is day-neutral and begins to

flower and set seed in July rather than in late-September as is the case for common

aeschynomene (Aeschynomene americana). Thus evenia may be more reliable at

reseeding than aeschynomene (Kalmbacher et al., 2002). The nutritive value of evenia is

similar to common aeschynomene, but unlike common aeschynomene, it has a

characteristic smell and is not immediately palatable to cattle. Cattle need time to adapt to

this legume and they will only graze small plants (Chambliss and Kalmbacher, 2000). It

also gets more "woody" than common aeschynomene. Evenia is more vigorous, more

persistent, and requires less management than common aeschynomene (Pate, 2001). The

growing season is from April to November and it produces more fall forage than common

aeschynomene (Sollenberger, 2002).

Mislevy and Martin (2001) reported that whole-plant CP of evenia was 224, 198,

and 206 g kg-' in 30, 60, and 90-cm tall plants, respectively. The IVOMD for the same

experiment was 625, 581, and 571 g kg-', respectively, when plants were clipped at a 10-

cm stubble height. Kalmbacher et al. (2002) reported a range in leaf CP from 215 to 308

g kg-'and stem CP of 67.9 g kg-' In vitro organic matter digestibility in leaves ranged









from 329 to 505 g kg-' and was 274 g kg-' in stems. In vitro organic matter digestibility of

stems did not change over time.

Studies by Kretschmer et al. (1994) indicate plant populations of evenia were >50%

after 5 yr of clipping. Forage nutritive value of the top 30 cm of plants averaged 265 and

671 g kg-' CP and IVOMD, respectively, in a space-planted nursery.

Shaw Creeping Vigna (Vignaparkeri Baker)

Creeping vigna is indigenous to Uganda, Kenya, and Tanzania (Verdcourt, 1970).

It was introduced by N. H. Shaw from the Veterinary Farm, Entebbe, Uganda, and was

registered in Canberra, Australia, on 3 Dec. 1958. The cultivar Shaw, released in 1984, is

recognized as the premier summer legume for dairy pastures in coastal southern

Queensland and northern New South Wales, but its widespread commercial use is

constrained by seed availability (Loch, 2002). Creeping vigna is a perennial herb, with

both twining and prostrate stems, the latter often developing nodal roots and forming

dense mats. Creeping vigna's growing points and dormant buds are protected from heavy

grazing when they are grown with grasses. Pitman and Kretschmer (1984) found that

close grazing provided a competitive advantage for creeping vigna since it spread

considerably during the growing season through elongation of short stolons, which rooted

at the nodes.

Creeping vigna will grow on a range of soils, from sands to heavier, but well-

drained, red clays, especially on hill slopes, and can tolerate moderately low fertility and

pH if fertilized with P and Mo (Humphreys and Partridge, 1995). Creeping vigna is a

promising forage legume, but problems have been encountered with stand establishment

and low tolerance to water stress (O'Donnell et al., 1992)









No grazing trials have been conducted to generate animal performance data on

creeping vigna based pastures on the far North coast of Australia. However, farmers with

commercial creeping vigna- based pastures report improved livestock performance.

Creeping vigna contributes to pasture digestibility and protein levels in late summer and

autumn, when dry matter digestibility commonly drops below 600 g kg -'and protein

levels fall to 70 g kg-'. The Commonwealth Scientific & Industrial Research Organization

(CSIRO) has measured uncorrected in vitro dry matter digestibility of creeping vigna at

650 g kg-' (leaf) and 550 g kg-' (stem). Leaf digestibility does not change greatly

throughout the season (Bede, 2002). Like most legumes, creeping vigna has high

nutritive value. Australian literature has reported leaf and stem CP at 250 and 120 g kg-,

respectively, with TDN at 610 and 550 g kg-', respectively. A study at the Range Cattle

REC by Pitman in 1981 showed that out of 19 legumes tested, creeping vigna was the

most persistent under grazing in a mixture with bahiagrass (Pitman and Kretschmer,

1984). Limited and expensive seed and lack of animal performance data are the main

reasons creeping vigna has not become more popular among cattlemen in Florida.

Grass-Legume Mixtures

In many tropical areas, N deficiency is a major limitation to pasture productivity.

Tropical legumes are widespread in the American tropics, where soil N in many

situations is low and provides a competitive advantage to the legumes (Pitman, 1994). A

viable alternative to grass with N fertilizer is legume-grass pasture. Legume-based

pastures are a good alternative for forage production. There are two major advantages

compared to grasses: i) only legumes can fix significant amounts of atmospheric N and ii)

legumes provide greater nutrient intake potential for ruminants thereby allowing more

efficient animal production. Legumes grown with grasses have several advantages over









grasses grown alone. Baylor (1974) noted that including legumes in temperate pastures

usually results in increased yield, high quality, and improved seasonal distribution of

forage. Legume-grass mixtures had reduced weed encroachment and erosion and led to

greater stand longevity than legume or grass monocultures (Droslom and Smith, 1976).

Results from Sleugh et al. (2000) suggest that including legumes with grasses can

improve IVOMD, CP, neutral detergent fiber (NDF), and seasonal distribution of forage

yield. The higher animal performance obtained with legumes is attributed to higher CP,

digestibility, and minerals, resulting in higher intake potential (Marten, 1985). Although

exceptions exist, compatible legume-grass mixtures usually yield more than any single

component grown in monoculture (Roberts and Olson, 1942, Aberg et al., 1943).

Alternatives to supply nutrients to cattle grazing bahiagrass in late summer include

growing a legume with bahiagrass, feeding supplements, or switching to one of the

specialty grasses. Bums and Standaert (1985), in an extensive review of grazing

experiments in the United States, reported that steer daily gains from legume-grass were

0.14 kg d-' more than from N-fertilized grass and calf daily gains were 0.15 kg d-'greater

on legume-grass in cow-calf experiments. Daily gains of yearling steers grazing

bahiagrass without a legume averaged 0.27 kg hd -'during summer but increased to 0.45

kg hd- when grazing common aeschynomene-bahiagrass pastures (Hodges et al., 1976).

However, some of the major difficulties in promoting grass-legume mixtures in the

humid tropics have been identifying legumes which are adapted to the prevailing

environmental conditions, are compatible with aggressive grass species, and able to

withstand heavy grazing (Ibrahim and Mannetje, 1998). According to Sheaffer (1989),

the risk of forage legume establishment failure is associated with small seed size and a









lack of seedling vigor. Limitations in water, light, and nutrients are major constraints to

legume seedling persistence. Cutting trials have shown that the erect types such as stylo

(.Snl,\1uinthr guianensis), and the twining climbing types of tropical legumes, such as

siratro (Macroptilium atropurpureum DC.), Desmodium intortum, and Neonotonia

wightii are sensitive to the frequency and height of defoliation, and that severe defoliation

can lead to rapid depletion of legume content (Jones, 1967; Whiteman, 1969). Creeping

legumes such as creeping vigna are less vulnerable to grazing at high stocking rates

(Bryan and Evans, 1973; Jones and Clements, 1987). The survival of some legume

species and cultivars under grazing is assisted by changes in growth habit in response to

defoliation. For example, creeping vigna tolerates close grazing by growing close to the

ground and rooting from stolons, but twines upward around associated grasses under light

grazing (Jones and Clements, 1987). "Incorporating legumes into our pasture increases

forage quality, increases animal performance, and reduces pasture costs per animal.

Although forage legumes can require more management than grasses, their high quality

can make a big difference in animal performance even if legume production is limited"

(Bade, 1998).

Forage Quality

Forages consumed by Florida livestock vary in quality due to differences in

genotype, maturity, season, and management. When quality is low, forages alone may not

support desired rates of animal performance (Moore and Sollenberger, 2002). Quality

(energy value) of warm-season perennial grasses often just barely meets the animal's

requirements, or is below requirements of the beef animal during the growing season.

Crude protein levels below 70 g kg-' could also limit forage intake (Milford and Minson,

1965). Typically, these grasses are highest in quality in the spring, decline from June









through August, then increase to October or November and rapidly decline after a freeze

(Bade, 1998).

The quality of the forage in any given pasture is a function of three separate but

related factors; the kinds of plants present, their stage of maturity, and the time of year.

Generally, the leaves of legumes are higher in quality than the leaves of grasses; grass

leaves are almost always of a higher quality than the stems of either legumes or grasses

(Darrell et al., 1993).

Grazing Systems

A grazing system is defined as an integrated combination of animal, plant, soil, and

other environmental components and the grazing method by which the system is

managed to achieve specific results or goals. An inventory or estimate of how much

forage is or will become available for grazing is the basis of projecting how many

animals can be grazed and for how long (Vallentine, 2001). Heardy (1970) defined a

number of terms as follows: the grazing season is that portion of the year during which

grazing is feasible. It may be year-long or shorter depending upon environmental or other

restrictions of the area to grazing livestock. Grazing period is that portion of the grazing

season during which grazing takes place.

Grazing Management

In order to optimize the yield and quality of forage produced from pasture, they

must be grazed at a frequency, intensity, timing, and duration that allow the plants to

remain both healthy and continually producing large quantities of high quality green leaf

material (Darrell et al., 1993).









Continuous Stocking

Continuous stocking is a method of livestock deployment where livestock have

continuous or uninterrupted use of a unit of grazing land throughout the time period in

which grazing is allowed. The disadvantage of continuous stocking is that it allows little

control of the timing of grazing. Under continuous stocking, livestock should be stocked

at a rate that will balance the feed requirement of the herd with the forage growth rate

(Rayburn, 1992). When grazing is prescribed so that there is an adequate supply of forage

available to meet or exceed the dry matter requirements of the planned number of

animals, gains per animal are often equal to or greater than those obtained with the

rotational stocking method. This is primarily the result of selective grazing (Emmick and

Fox, 1993).

An improved management strategy for increasing the harvest efficiency of pastures

that are continuously stocked is to alter the number of grazing animals in response to the

amount of available forage. This is generally described as a "put and take or variable

stocking rate style of grazing management. Although pastures that are managed using this

strategy may be continuously stocked during the period of time in which grazing is

allowed, the forage supply is constantly monitored and adjustments to the stocking rate

made by increasing or decreasing the number of grazing animals in response to the

available forage supply (Emmick and Fox, 1993). With continuous stocking, the taller

more productive plant species tend to decline in productivity and abundance. With the

rotational stocking method, these plants can remain productive and persistent for many

years (Darrell et al., 1993).









Rotational Stocking

Rotational stocking is where livestock are moved between pastures during the

grazing season, concentrating their feeding on one pasture for a few days and then

moving to a new field that is ready to graze. The grazed paddock is allowed to rest and

regrow for a suitable length of time. The time needed depends on the forage species and

growing conditions (Rayburn, 1992). Rotationally stocked pastures suffer from the

disadvantage of requiring greater management and they limit opportunity for animals to

graze forage selectively. Research in Scotland and some other countries has shown that

well managed continuous stocking of pastures can be easier to accomplish, relative to

rotational grazing, and can give levels of performance in the animal that exceed those

achieved with rotational or strip grazing (Buchanan-Smith and Watson, 1999).

Grazing Intensity

The relationship between stocking rate and live weight gain of animals has been

summarized by Hart (1978). Grazing intensity (frequency and closeness of grazing)

regulates the opportunity of animals to graze selectively. As grazing intensity increases

due to increased stocking rate (or grazing pressure), there is less herbage available per

animal, thus animals become less selective in choosing the plants and plant parts eaten in

order to become satiated. Correspondingly, as stocking rate increases, the level of plant

defoliation increases along with changes in sward morphology and composition (Matches

et al., 1981). The optimum stocking rate will always be somewhere between that which

maximizes individual animal performance and that which maximizes animal performance

per hectare (Clifford, 1998).

Stocking rate refers to the forage demand per unit of land area for a specified length

of time (Clifford, 1998). Stocking rate is considered the most important variable in









grazing management; unless it is near the proper level, regardless of other grazing

practices, the objectives of grazing management will not be met (Walker, 1995). Over the

short term, a heavy stocking rate may lower forage quality by removing green foliage and

forcing animals to consume more dead, standing forage (Lyons and Machen, 2001).

Seasonal and total forage dry matter production and nutritive value should be matched

with livestock requirements. The most efficient means of matching warm-season

perennial forage with livestock is by the use of a variable stocking rate (Rouquette,

1993). A number of factors include animal species, size and physiological stage, size of

the pasture or ranch, and number of grazeable hectares (Lyons and Machen, 2001).

Increasing stocking rates on pastures decreases quantity available for each grazing

animal. This will decrease the opportunity for selectivity by the animal, and in stocker

animals, decrease the average daily gain. Gain per hectare, however, is increased by

heavier stocking as long as forage quantity is present (Bade, 1998). Stocking rate

recommendations should be based more on potential forage intake than on numbers of

animals (Lyons and Machen, 2001).

Herbage Allowance

Herbage allowance is defined as the amount of dry forage allowed per 100 kg

animal body weight daily (Adjei et al., 1980). Herbage allowance affects the quality of

the diet that the animals can select, because the animal must select its diet from among a

variety of different plants and plant parts of varying quality (Clifford, 1998). Smith and

Whiteman (1985), in an experiment conducted in the Solomon Islands, using rotational

stocking with an allowance of only 10 kg of DM kg- LW d 1 for a 28-d period, measured

a maximum live weight gain of 400 g d'. On the same natural pastures (main species

present Axonopus compressus, C. pubescens, M. pudica, and Calopogonium mucunoides;









minor species: P. conjugatum, D. heterophyllum, D. canum, P. phaseoloides, Synedrella

nodiflora, Borreria sp., Peperomiapellucida, and Mikania s.p). in a continuously stocked

grazed experiment, Watson and Whiteman (1981) found that a maximum live weight

gain occurred when an allowance of up to 10 kg of DM kg' LW d- was given.

Grazing management involves constant evaluation of total herbage mass (HM), the

period during which estimated HM will be utilized, and the stocking rate (SR) required

for such utilization. The rotational stocking method is defined by a specified period of

grazing (GP) alternated with a specified period of rest (RP) within a grazing cycle. Based

on the GP and RP, a specific number of cycles are completed within the grazing season.

The bulk of forage produced on a paddock in a rotational system is consumed during the

GP and forage accumulation during the RP must depend on reserve carbohydrates and

residual leaf area. The daily herbage allowance method (Adjei et al., 1980) for rotational

stocking is calculated by dividing the total expected HM by the GP and expressing the

result as a percentage of the animal stocking rate. The converse can be used to determine

animal stocking rate (kg BW ha-) for an assigned herbage allowance and estimated total

HM.

For a continuous stocking method, there are no defined periods of grazing and rest

and the GP is actually equal to the grazing season. To be sustainable, the system must

maintain sufficient HM and herbage accumulation rate at all times to support the number

of assigned grazing animals. It is conceivable to spread the total estimated HM

(instantaneous HM + expected herbage accumulation) at each point in the grazing season

to cover the remainder of the season when calculating stocking rate at the assigned daily

herbage allowance under the continuous stocking method. Subsequent adjustments in the









stocking rate are then made periodically based on the concept of spreading total HM to

cover the remaining time in the grazing season.

Williams and Hammond (1999) have described a continuous intensive stocking

method in which stocking density was temporarily increased by 75% during periods of

rapid forage accumulation and the excess forage reserved as a potential for hay

production. This was done to improve animal performance by matching herbage

accumulation rate with forage utilization and preventing accumulation of low quality

forage.

Nutritive Value

Animal production is a function of the daily intake of digestible dry matter and

therefore depends on both the quantity of food eaten and the digestibility of the feed

(Holmes et al., 1966). Forage nutritive value is often described as chemical composition

and digestibility.

Deficiencies of dietary protein depress intake of dry matter. In tropical grasses, CP

below 70 g kg-' may depress dry matter intake (Milford and Minson, 1965). Crude protein

in N-fertilized bahiagrass in April ranged froml20 to 150 g kg -1DM, and CP of

unfertilized grass ranged from 90 to 120 g kg-'DM (Kalmbacher and Wade, 2003).

Minson (1980) stated the range for CP concentration of bahiagrass is often near the 60 to

80 g kg- DM. Some legumes have a higher nutritive value than grasses that result in

better animal performance. Legumes contain five times the Ca, 30 to 50% more P, and

twice the Mg of grasses (Evers, 2001). Animals have certain nutritive requirements based

on class, age, and expected performance (gain, milk, etc.). In general, the younger the

animal or the greater the expected performance level, the greater is the requirement for

forage to be of high quality (Rouquette, 1993)






17


Digestibility declines as lignin concentration increases, but the relationship

between lignin concentration and digestibility varies among species (McLeod and

Minson, 1974). In tropical grasses as lignin concentration increases digestibility

decreases, in legumes this relationship may be less consistent. As the pasture sward

matures, tropical legumes generally have greater dry matter digestibility (DMD) and

voluntary intake than the associated grass (Playne and Haydock, 1972). Legume grazing

can increase daily gains of cattle during the late summer and fall period (Hodges, 1978).














CHAPTER 3
MATERIALS AND METHODS

General Description of the Experimental Area

The experiment was conducted from September through December 2001 and from

May through November 2002 at the Range Cattle Research and Educational Center

(REC), Ona, which is part of the Institute of Food and Agricultural Sciences, University

of Florida.

The center is located 820 55' W and 270 26'N in south central Florida (Hardee

county). Climatological data shows that the average monthly minimum temperature is

110C. Frosts are most likely to occur in December, January, and February. The 61-yr

mean annual precipitation is 1362 mm. The months of June through September receive

the highest rainfall, and April/May the lowest rainfall (Table 3.1). Because of this rainfall

pattern, frequent and short- to long-term flooding occurs on pastures in summer and

severe droughts in the spring. The soils are described as Pomona fine sand (sandy,

siliceous, hyperthermic Ultic Haplaquod).

Experimental Procedures

Legume-grass Mixture

The legume-grass mixtures selected for the experiment were evenia and creeping

vigna, both with bahiagrass cv. Pensacola. Bahiagrass was selected because it is the most

important pasture grass cultivated in Florida. It is drought tolerant, grazing persistent,

adapted to flooded soils, and grows in mixtures with most tropical legumes. Evenia has

high protein levels and is generally adapted to the moist flatwoods areas in the state.









Creeping vigna shows persistence under grazing, high nutritional value, and compatibility

with aggressive grasses such as bahiagrass.

Pasture Establishment

Legumes were planted into established bahiagrass pastures. For legume

establishment, we used close grazing (5-cm stubble height) by cattle before and

immediately after sod-seeding until legume seedlings were about 8 cm tall. Then, cattle

were withdrawn from pastures, and the legume was allowed to grow and become

established. Legumes were sod-seeded with a no-till seeder at 12.4 kg ha- for evenia on 1

June 2001 and 5.1 kg ha-' for creeping vigna on 31 May 2001. Evenia was reseeded at

11.2 kg ha- on 29 April 2002. Legume seeds did not receive any mechanical or chemical

treatment, rhizobial inoculum, or fertilizer during establishment in 2001, because some

common aeschynomene normally occurs in these areas. In December 2001, soil samples

were taken and analyzed. In Spring 2002, pastures were limed to pH 5.5 according to soil

test recommendations and received a uniform application of 15 kg ha- P, and 56 kg ha- K

(336 kg ha-' of 0-10-20) plus micronutrients: total Ca 3.3 g kg-', S (combined) 1.00 g kg-',

Chlorine-not more than 20.00 g kg-', B 0.05 g kg-', soluble Cu 0.50 g kg-', soluble Fe 0.50

g kg-1, soluble Mn 0.50 g kg-', Zn 0.50 g kg-', derived from triple superphosphate,

superphosphate, manganese sulfate, copper sulfate, iron sulfate, zinc sulfate, and sodium

borate. No N was applied because we depended on the legumes to fix atmospheric N.

Treatment and Experimental Design

The treatments compared in this study were 1) evenia-bahiagrass, 2) creeping

vigna-bahiagrass, and 3) pure bahiagrass. Pastures were arranged in a randomized

complete block design. Each treatment was replicated twice in 2-ha pastures and the total

number of experimental units was six. The replications represented the blocks. Pastures









were stocked continuously at a variable SR (based on herbage allowance) with growing

steers. The variables measured were HM, botanical composition and density, IVOMD,

CP, tissue chemical composition (P, K, Ca, Mg, Zn, Mn, Cu and Fe), cattle average daily

gain (ADG), and gain per hectare.

Pasture Samples

Grazing Experiment

In 2001, the experimental period was from September to December (86 d). The

grazing season for warm season forages is from May to November, but grazing started

late due to the slow establishment of the legumes. Only the evenia-bahiagrass and pure

bahiagrass pastures were sampled in 2001 because the creeping vigna pastures were not

well established.

In 2002, the experimental period was from May to December (168 d) and the

evenia-bahiagrass, creeping vigna-bahiagrass, and pure bahiagrass pastures were

sampled. Forage samples were taken from pastures in September, October, and

November 2001 and in May, June, July, August, September, and October 2002. The

direct method was used to estimate herbage mass. Forage from six, 0.5-m2 quadrats with

representative herbage mass were clipped to a 2.5-cm stubble from each pasture on each

sampling date with an electric sheep wool shears powered by a generator. In pastures

with grass-legume mixture, legume and grass were placed in separate bags at harvest.

Pastures were sampled at 28-d intervals. The samples were dried at 60 OC to constant

weight (48-72 h) in a forced-air oven. Herbage mass (kg DM ha') was calculated as

measures of available forage in pasture determined from the mean dry weight.









In 2002, herbage accumulation (HA) was estimated by using three exclosure cages,

which were installed on each pasture. Each cage was 1m2 in size. The cages were paired

with three of the outside cage samples and moved to a new location in the pasture every

28 d after harvesting inside and outside the cages to estimate herbage accumulation. The

areas selected for the placement of the cages and harvested outside of cages were paired

to represent average forage mass in the pastures.

Botanical Composition

Botanical composition of the pastures was determined as percentage by weight

from the same samples used to estimate herbage mass. Botanical composition was

calculated as the summation of component herbage mass (over grazing cycles) x 100 and

divided by the summation of total herbage mass. The persistence of the legume was

determined by conducting vegetation analysis on the grass-legume pastures over time.

Data were collected in September 2001. For the year of 2002, legume stand density in

pastures was measured in May, June, July, August, and October. A 1-m2 quadrat was

used to estimate the plant density. Eight line transects were laid evenly across each

pastures on a zigzag pattern. Along each transect, the quadrat was dropped at

approximately 6-m intervals to provide eight points for sampling. This gives a potential

for 64 (8*8) occurrences. When the quadrat was dropped at each point, the number of

evenia or creeping vigna plants inside the quadrat was counted.

Chemical Composition

The grass and legume components were ground to pass through a 1-mm screen in a

Wiley Mill. Before grinding, evenia samples from year 2001 were separated into edible

(leaves and small stems < 3 mm diameter) and non-edible sections (stems > 3 mm),

because plants were big and stemmy. Evenia plants from year 2002 were not separated









into edible and non-edible parts because plants were small (stems < 3 mm diameter).

Analyses for IVOMD and CP were performed at the Forage Evaluation Support

Laboratory of the University of Florida. The IVOMD of the grass and legume was

determined by a Tilley and Terry (1963) procedure as modified by Moore and Mott

(1974). The CP concentration was determinate by a micro-Kjeldahl procedure.

Tissue minerals were extracted from samples using the ashing/0.3025 M HC1

extraction method. Tissue P, K, Ca, Mg, Zn, Mn, Cu, Fe concentrations were determined

at the Analytical Research Laboratory of the University of Florida using the Inductively

Coupled Argon Plasma Spectroscopy method (Thermo Jarrell Ash ICAP 61E, Franklin,

MA).

Animal Performance

Daily herbage allowance was used to adjust the number of animals per paddock

every 28 d following HM estimation. Stocking rate (kg BW ha-') d-'was calculated by

dividing each herbage fraction (the herbage mass or herbage accumulation [kg DM ha-'])

by the appropriate number of days that forage component would be utilized, and then

divided by assigned herbage allowance (kg DM [100 kg animal BW]-'d-).

In 2001, the herbage allowance used was 5, 8, and 10 kg DM (100 kg animal BW) 1

d- for the months of September, October, and November, respectively. Variable herbage

allowance was used because we want to determine the desirable level to be use in

subsequent years of study. The estimated HM was spread to cover the remaining period

of the grazing season, because we were unsure of the growth rates of bahiagrass during

this period, and we did not want to run out of forage because we want to keep animals

until December, and estimated HM was spread over 90 d in September, 60 d in October

and 30 d in November (Appendix Table A. 11).









In 2002, a constant herbage allowance of 10 kg DM (100 kg animal BW)1 d'l was

utilized. In 2002, both estimated HM and herbage accumulation were used when

calculating SR. Stocking rate of the pasture was calculated as the sum of the SR for

estimated HM and carrying capacity for herbage accumulation. The SR for the HM

fraction, in May, June and July, was estimated on a 30-d cycle, based on the concept of

continuous intensive stocking (Williams and Hammond, 1999). However, from August to

October, the estimated HM was spread over the remaining grazing season, 90 d in

August, 60 d in September, and 30 d in October. The SR for the herbage accumulation

fraction, was calculated based on a 30-d usage of HA throughout the trial (Appendix

Table A. 12).

Three crossbred steers (Brahman x British) and three Brangus steers were assigned

as testers to each pasture in 2001 and 2002, respectively. Put-and-take animals were

added and removed every 28 d as needed to maintain the assigned herbage allowance.

Average tester weights at the start of the experimental period were 350 and 230 kg in

2001 and 2002, respectively. Steers were 21 and 12 mo of age in 2001 and 2002,

respectively, at the start of the trials. Individual animal weights (tester and put-and-takes)

were taken at 28-d intervals (no shrunk steers weights) and were used to guide the

addition or removal of put and take animals from pastures based on the assigned herbage

allowance. The seasonal ADG was calculated as the difference between the final and

initial weight of testers divided by the days of grazing season. The cumulative ADG for

each month was calculated as the difference between weight of testers at the end of a

month and initial weight of testers (weight at beginning of grazing season) divided by the

number of days that animals had been on the pasture up to that point.









Seasonal carrying capacity was calculated using both testers and put and take

animals, and it was expressed in kg of live weight per hectare per day. Animal days per

hectare were determined using all animals but were adjusted for the weight of the average

tester. Seasonal gain per hectare was calculated as the product of ADG and animal days

per hectare.

Minerals were supplemented to steers ad libitum. The mineral supplement used was

FRS Mineral manufactured by Lakeland Animal Nutrition, (Lakeland, FL) with the

following mineral composition: Ca max. 14 g kg- min. 12 g kg-', P min. 9 g kg-', NaCl

max. 24 g kg-', min. 12 g kg-', K min. 0.20 g kg-', Mg min. 0.30 g kg-', S min. 0.20 g kg-',

Co min. 50 mg kg-', Cu min. 1500 mg kg-', I min. 210 mg kg-', Mn min. 500 mg kg-', Se

min. 40 mg kg-', Zn min. 3000 mg kg-', F not more than 800 mg kg-', and vitamin A (min.

180000 IU/lb).

Statistical Analysis

The data were analyzed using least-square analysis of variance (SAS, PROC

mixed). The design was a randomized complete block design with two replicates. The

model included treatment (evenia-bahiagrass, creeping vigna-bahiagrass, and pure

bahiagrass), month, and replicates. Analysis of variance was used to determine treatment

differences in IVOMD, CP, chemical composition, ADG, and gain ha-'. The PDIFF

method was used for mean separation.









Table 3.1. Millimeters of rainfall by month in 2001, 2002, and 61-yr average at the Range
Cattle REC.

Month 2001 2002 61-year average


Jan 9 47 57

Feb 1 158 65

Mar 161 11 81

Apr 24 65 64

May 33 33 94

Jun 269 352 215

Jul 362 281 218

Aug 257 311 205

Sep 451 139 185

Oct 61 62 80

Nov 4 120 49

Dec 12 179 50

Total 1643 1756 1362














CHAPTER 4
RESULTS AND DISCUSSION

Forage Responses

Herbage Mass of Sward Components

Bahiagrass

In 2001, there was no treatment x month interaction for bahiagrass component HM

(P>0.05, Appendix Table A. 1). Mean HM of the bahiagrass component was not different

between treatments, and averaged 4150 kg ha- (P>0.05, Appendix Table A. 1). Mean HM

of bahiagrass across treatments was greater (P<0.05) in October (4900 kg ha-) than

September or November (Fig. 4.1). Bahiagrass HM increased from September to October

and then decreased by November. This decline in HM corresponded to decreasing day

length and temperature, because bahiagrass growth decreases as days become shorter.

In 2002, there was no treatment x month interaction for bahiagrass HM (P>0.05,

Appendix Table A.2). Mean HM of bahiagrass was not different among treatments, and

averaged 2620 kg ha- (P>0.05, Appendix Table A.2)

A difference (P<0.05) in bahiagrass HM among months was detected; September

(3320 kg ha-) had greater HM than June (1710 kg ha-') that had the lowest HM (Fig. 4.2).

This was due to heavier stocking rate in anticipation of rapid forage regrowth, but growth

was slower than expected.

HM of bahiagrass in 2001 showed greater values, compared with those obtained in

2002 because grazing started late in 2001 when bahiagrass had accumulated to a greater

extent than in 2002. HM of bahiagrass in 2002 was low because grazing started early no









N fertilizer was applied to the pasture, and there was little contribution of N from the

legume to the pastures.

Evenia

In 2001, HM of evenia stems was greatest (P<0.05) in September and October (380

and 270 kg ha-', Table 4.1), than in November, as a result of forage accumulation prior to

grazing. Plants were bigger and evenia tends to be stemmy and woody. Following the

start of grazing, the amount of evenia stems decreased. In the first month, the leaf/stem

ratio was 1:1 but as times went on the percentage of evenia leaves increased, because of

plant regrowth and branching into small stems. Evenia leaf mass was not different among

months and averaged 290 kg ha-' (P>0.05, Table 4.1). In 2002, HM of evenia did not

change over time averaging 100 kg ha-' (P>0.05).

Creeping vigna

In 2001, the creeping vigna-bahiagrass pasture was not sampled because it was not

well established. In 2002, HM of creeping vigna did not change over time averaging 190

g kg- (P>0.05).

Botanical Composition

Evenia-bahiagrass

In 2001, total HM of the pasture (bahiagrass 4440 kg ha-' and evenia 540 kg ha-')

was 4960 kg ha-1, the contribution of bahiagrass represented 89% and evenia represented

11%. In 2002, total HM of the pasture (bahiagrass 2490 kg ha-' and evenia 100 kg ha-')

was 2590, the contribution of bahiagrass to total HM represented 96% and evenia

represented 4%. In 2001, grazing started in September, so evenia was well established at

the start of grazing. In 2002, grazing started in May, and evenia plants although

established, were still small and it is possible that steers kept eating the small evenia









plants, not allowing them to grow. Therefore the contribution of evenia to total HM in

2002 was less than 2001.

Creeping vigna-bahiagrass

In 2002, total HM of the pasture (bahiagrass 2850 kg ha-' and creeping vigna 190

kg ha-) was 3040 kg ha-', the contribution of bahiagrass represented 94% and evenia

represented 6%. Vigna did establish well during the second year but growth was low to

the ground.

Density

For the year 2001, only one plant count was made in September, in the evenia-

bahiagrass treatment. The density of evenia was 12 plants m-2. In year 2002, legumes

were counted four times during the grazing period, May, June, August, and October.

Density did not change over time (P>0.05), averaging 6 evenia plants m-2 and 13 vigna

plants m-2.

Crude Protein

Bahiagrass

In 2001, CP concentration in the bahiagrass component was highest (P<0.05) in

September at 70 g kg-' and declined with time probably as a result of accumulation of

mature forage (Fig. 4.3). No treatment x month interaction was detected (P>0.05,

Appendix Table A.3). Crude protein of the bahiagrass component across treatments was

not different with a mean of 65 g kg- (P>0.05, Appendix Table A.3). Low bahiagrass CP

in the pastures resulted from no N fertilizer application and probably very little

contribution of N from either evenia or creeping vigna.

In 2002, there was no treatment x month interaction in CP on the bahiagrass

component (P>0.05, Appendix TableA.4). Crude protein concentration of the bahiagrass









component across treatments was not different with a mean of 77 g kg-' (P>0.05,

Appendix Table A.4). Crude protein concentration in bahiagrass was greater (P<0.05) in

June and July with 86 and 91 g kg-' (Fig. 4.4). During May, rainfall was low, so HM of

bahiagrass in June and July was low, and the CP was more concentrated and that

probably explains the greater CP concentrations reported in this period. These bahiagrass

CP levels in this experiment fall within the range of values (77-98 g kg-') reported by

Arthington and Brown (Unpublished data).

Evenia

In 2001, evenia plants were separated into edible (leaves and stems <3 mm) and

non-edible (stems> 3 mm) parts. Crude protein concentration in the edible part of evenia

plants changed (P<0.05) over time, decreasing from 190 (September) to 160 g kg-'

(November). The non-edible part was affected by month (P<0.05) decreasing from 84

(September) to 59 g kg-' (November) (Fig. 4.5). Crude protein of the edible part of the

legume was low compared with the CP concentration in evenia leaves reported by

Kalmbacher et al. (2002; CP ranged from 215 to 308 g kg-'). This was probably due to the

inclusion of stems <3 mm in the edible fraction.

Kalmbacher et al. (2002) reported that CP of evenia stems averaged 67.9 g kg-' and

did not change over time. In the current study, CP of stems >3 mm was different over

time, being greater at the first sampling date (September) and then declining by the end of

the grazing season, as a consequence of plant maturity. In 2002, CP in evenia was not

different over time averaging 162 g kg-' (Appendix Table A.5). Crude protein of evenia

was low compared with the 215 g kg- in evenia plants that were 30-cm tall (Mislevy

and Martin, 2002). Evenia plants sampled were shorter than 30 cm, and they had more

stems than leaves at the time, and this could be the reason why CP was lower for evenia









plants than those reported in the literature.

Creeping vigna

In 2002, CP of creeping vigna was not different (P>0.05) over months, averaging

193 g kg-' (Appendix Table A.5). Australian literature has reported leaf and stem CP of

creeping vigna at 250 and 120 g kg-' respectively, (Bede, 2002), the average of which is

similar to CP of whole creeping vigna plants in this study.

In Vitro Organic Matter Digestibility

Bahiagrass

In 2001, an interaction between treatment and month was found (P<0.05) for the

bahiagrass component IVOMD. In both treatments, IVOMD of the bahiagrass component

was greatest in September and decreased progressively in November. The IVOMD of the

bahiagrass component from the bahiagrass-evenia mixture was lower compared with the

bahiagrass component from the bahiagrass alone pastures in September (Table 4.2). The

IVOMD between treatments was not different in October with a mean of 365 g kg-'

(P>0.05, Table 4.2) but by November the IVOMD of the bahiagrass component from the

pure bahiagrass pasture treatment was lower than the bahiagrass component from the

mixture. The decrease in digestibility of the bahiagrass component occurred because

plants became mature, tissue became lignified with time, and the quality of the grass went

down.

In 2002, there was no a treatment x month interaction for the bahiagrass component

IVOMD (P<0.05, Appendix Table A.6). The IVOMD of the bahiagrass component

among treatments was not different averaging 404 g kg-' (P>0.05, Appendix Table A.6).

Across treatments, IVOMD of the bahiagrass component was different (P>0.05) through

time, reaching 444 g kg- in July, and then as the plants became mature decreasing to 360









g kg- in October (Fig 4.6). Arthington and Brown (unpublished data) reported bahiagrass

IVOMD values in the range of 540 to 475 g kg- under clipping frequency of 4 to 10 wk,

respectively, and with N fertilizer.

Evenia

In 2001, IVOMD of the non-edible part of evenia was not different (P>0.05)

through time, with an average mean of 240 g kg-' (Appendix Table A.7). The IVOMD of

the edible part of the legume was greater (P<0.05), in September (561 g kg-') and then

decreased by November (489 g kg-') (Fig. 4.7). The IVOMD of the edible part of evenia

reported in this study was greater than that of evenia leaves (239 to 505 g kg-') as reported

by Mislevy and Martin (2001).

Evenia plants sampled in 2002 were not separated into edible and non-edible parts

because all plants were small. Plants were analyzed as a whole. The IVOMD of evenia

plants remained the same throughout the season with a mean of 537 g kg-' (P>0.05,

Appendix Table A.8). This IVOMD was low compared with the IVOMD of 613 g kg in

30-cm high evenia plants reported by Mislevy and Martin (2001). Evenia plants analyzed

for IVOMD in this study contained more stems than leaves, which explains why the

results were lower than those reported in the literature.

Creeping vigna

In 2002, IVOMD increased from 634 g kg-' (June) to 726 g kg-' (October) (Fig.

4.8). The IVOMD reported in this study, was greater than that from Australia where

uncorrected in vitro dry matter digestibility was 650 g kg- in the leaf and 550 g kg- in the

stem (Bede, 2002).









Tissue Mineral Composition

Bahiagrass

In 2001, the concentrations of P, Ca, K, Mg, Zn, Mn, Fe, and Cu in the bahiagrass

component were not different between treatments (P>0.05, Appendix, Table A.9).

Concentration changed over time (P<0.05) for most minerals. Phosphorus (2.0 g kg-) and

Mg (3.9 g kg-') concentrations were not different over time, but Ca, K, Zn, Mn, Fe, and

Cu concentrations varied. Calcium and Mn concentration increased from September to

November, and concentrations of K and Zn decreased from September to November

(Table 4.3).

In 2002, mineral concentration of the bahiagrass component from the three

treatments was not different (P>0.05, Appendix Table A.9). Mineral concentration in the

bahiagrass component was different (P<0.05) across months, as P, Ca, K, Zn, Mn, Fe,

and Cu tended to decrease as the grazing season progressed, but Mg tended to increase as

the season ended (Table 4.3).

Evenia

In 2001, the P (3.3 g kg-'), Ca (7.2 g kg-'), K (15.3 g kg-'), Zn (47.2 mg kg-'), Mn (186.2

mg kg-') and Fe (70.8 mg kg-') concentrations in evenia leaves did not change

(P>0.05, Table 4.4) throughout the season. Tissue Mg and Cu concentrations were

different among months (P<0.05, Table 4.4), with a range of 2.3 to 3.8 g kg- and 13.0 to

19.0 mg kg-', respectively. The concentration of both minerals tended to decrease towards

the end of the season.

In 2001, P (2.3 g kg-1), Ca (4.4 g kg-1), K (9.7 g kg-1), Mg (1.3 g kg-1), Zn (38.8 mg

kg-), and Mn (60.3 mg kg-) concentrations in evenia stems were not different (P>0.05,

Table 4.4) through the months. Iron and Cu concentrations varied (P<0.05, Table 4.4).









Iron increased from 24 mg kg-' in September to 72.5 mg kg-' in November. On the other

hand, Cu concentration was 23 mg kg-1 in September, decreasing to 12.5 mg kg- in

November.

Evenia DM samples collected from May to June 2002, were not sufficient for

mineral analysis. The concentration of minerals in evenia plants was not different

(P>0.05) among months. Average values for minerals were P (3.8 g kg-'), Ca (5.7 g kg-),

K (13.3 g kg-1), Mg (2.4 g kg-1), Zn (39.7 mg kg-1), Mn (59.3 mg kg-1), Fe (60.7 mg kg-1),

and Cu (10.7 mg kg-') (Appendix Table A. 10).

Creeping vigna

There was not enough creeping vigna samples in June for mineral concentration

analysis. Concentration of most minerals in creeping vigna was different among months

(P<0.05, Table 4.5). Manganese (72.2 mg kg-'), Mg (4.4 g kg-') and Fe (117.5 mg kg-1)

were not different across months but P (1.6-4.0 g kg-'), Ca (7.7-12.6 g kg-'), K (13.0-26.5

g kg-1), Zn (27.0-51.5 mg kg-') and Cu (8.5-30.5 mg kg-') differed among months.

Generally, creeping vigna sampled in May had a low concentration of the minerals. This

concentration increased through July and by August concentration had started to

decrease.

Animal Performance

In 2001, the seasonal ADG and gain per hectare of 320-kg long yearling steers over

the 86-d grazing period between evenia-bahiagrass (0.09 kg d-' and 9 kg ha-'), and pure

bahiagrass (0.16 kg d-' and 15 kg ha-) were not different (P<0.05). In 2002, seasonal

ADG and gain per hectare of 230-kg yearling steers over the 168-d grazing period were

not different (P<0.05) among evenia-bahiagrass (0.09 kg d-' and 21.5 kg ha-'), creeping

vigna-bahiagrass (-0.04 kg d-' and -7.5 kg ha-'), and pure bahiagrass (-0.01 kg d' and -1.5









kg ha-'). Animal performance in both years was poor. Stocking rate was adjusted every

month according an assigned herbage allowance in order to ensure sufficient quantity

forage for animals at all times during the grazing season. We consider that the quantity of

forage was not a contributing factor to low animal performance. It is likely that poor

animal performance was a result of poor forage quality. Forage CP and IVOMD declined

substantially toward the end of the grazing season, and the cumulative ADG also

decreased. (Appendix Table A. 11 and A. 12). Milford and Minson (1965) reported that

CP concentration below 70 g kg- could limit forage intake. In the present study,

bahiagrass CP was below 70 g kg-', which might have limited forage intake and as a

consequence reduced the ADG. Despite the fact that legumes provided forage of higher

nutritive value, ADG was not improved compared with bahiagrass alone, because the

proportion of the legume DM on pasture was low. Additionally, although nutritive value

of creeping vigna was high, IVOMD was 631 to 726 g kg-' and CP was 193 g kg-', it was

suspected that the young calves were unaccustomed to it and refused to consume

adequate amounts.

The ADG's reported in this study were very small compared with those obtained in

a previous study by Kalmbacher (1996) who observed that ADG of steers over a 112-d

period was not different between evenia-bahiagrass (0.68 kg h d-) and bahiagrass alone

(0.54 kg hd-'). In another study, Kalmbacher et al. (2002) reported that ADG was the

same for bahiagrass alone (0.39 kg hd-') and evenia-bahiagrass (0.45 kg hd-). Thus, in

both instances the inclusion of the legume did not improve ADG over pure grass, but

steers gained weight in Kalmbacher's study probably because animals were mature

heifers. In the current study, steers were 21 months of age (350 kg BW) in 2001 and 12










months of age (230 kg BW) in 2002. The steers apparently consumed forage that was

mainly sub maintenance and not sufficient for weight gain towards the end of the season.


6000

a
5000


Cu
4000
,0)

c 3000
E
,0)
- 2000
I

1000


0


Sept.


Oct.
Month


Nov.


Figure 4.1. Monthly HM of the bahiagrass component across treatments in 2001. Means
(bars) with different letters above them are different by PDIFF (P<0.05).










3500 a
a
3000 -
-_ b
o0 2500
( 2000 -
E 1500

0)
031000
(D 500


May June July Aug. Sept. Oct.
Month


Figure 4.2. Monthly HM of the bahiagrass component across treatments in 2002. Means
(bars) with different letters above them are different by PDIFF (P<0.05).










72
a
70

68

0 66 b

4 64

S62 -
0
60 -

58

56
Sept. Oct. Nov.
Month




Figure 4.3. Mean CP of the bahiagrass component across treatments in 2001. Means
(bars) with different letters above them are different by PDIFF (P<0.05).










100
90 a a
80 b b b b
70 -
60
6')
0 40
a 30
0
20
10 -
0
May June July Aug. Sept. Oct.
Month

Figure 4.4. Mean CP concentration in the bahiagrass component across treatments in
2002. Means (bars) with different letters above them are different by PDIFF
(P<0.05).


200
180
160
140
120
100
80
60
40
20
0


Sept.


Oct.


E Leaves
* Stems


Nov.


Month


Figure 4.5. Mean CP concentration in evenia leaves and stems in 2001. Means within a
plant part with a different letter above the bar are different by PDIFF
(P<0.05).










500


400
0
O
,) 300
-Z:
0)
0 200
0
S100


May June July Aug. Sept. Oct.
Month


Figure 4.6. Mean in vitro organic matter digestibility (IVOMD) of the bahiagrass
component across treatments in year 2002. Means (bars) with different letters
above them are different by PDIFF (P<0.05).


600
580
560
540
520
500
480
460
440


Sept.


Oct.


Nov.


Month

Figure 4.7. In vitro organic matter digestibility (IVOMD) of evenia leaves (leaves and
stems <3 mm) in 2001. Means (bars) with different letters above them are
different by PDIFF (P<0.05).






40



740 -ac
720 -
r a
O 700 -a
S68
(P660 .
S640 b
0 620 -
600 r
580
May June July Aug. Sept. Oct.
Month


Figure 4.8. In vitro organic matter digestibility (IVOMD) of creeping vigna in 2002.
Means (bars) with different letters above them are different by PDIFF
(P<0.05).





Table 4.1. Monthly HM (kg ha-) of evenia stems and leaves (leaves and stems <3 mm) in
year 2001.


Month Leaves Stems


Sep 290 a* 380 a

Oct 270 a 270 a

Nov 300 a 110 b

Mean 290 250


* Means within a column with different superscripts are different by PDIFF (P<0.05)









Table 4.2. In vitro organic matter digestibility (g kg-') of the bahiagrass component for
treatments and month in 2001.


Treatment
Month Evenia-bahiagrass Bahiagrass


Sept. 398 B a + # 420 A a

Oct. 368 Ab 361 Ab

Nov. 317 Ac 296 Bc

Mean 361 359

+ Means within a column with different lower case letters are different by PDIFF
(P<0.05)
# Means within a row with different upper case letters are different by PDIFF (P<0.05)










Table 4.3. Monthly tissue chemical composition of the bahiagrass component in 2001 and
2002.


P Ca K
g kg-_


2.1a*

1.9a

2.0a

2.0


2001

Sep

Oct

Nov

Mean

2002

May

Jun

Jul

Aug

Sep

Oct

Mean


2.1b

2.1b

2.5a

2.2


3.8a

3.7a

2.2c

2.2c

2.2c

2.5b


9.2a

9.7a

5.5b

8.1


14.9b

13.1c

17.0a

13.7c

11.6d

11.4d


Mg





3.8a

3.9a

4.1a

3.9



2.5c

2.8b

2.2e

2.4ce

2.8bd

3.0ad


2.6 2.8 13.6 5.2


Zn Mn


23.0a

24.5a

18.5b

22.0



25.5b

35.0a

26.0b

18.5c

17.5c

18.0c

23.4


134.5b

144.5b

196.5a

158.5



108.0a

118.5a

61.0b

48.5c

44.0c

42.5c

70.4


* Means within a column and year followed by different letters are different by PDIFF
(P<0.05)


Fe Cu


mg kg1_


2.6b

3.2a

2.7b

2.3c

2.3c

2.4c


42.5a

40.0a

56.0b

46.2



53.5b

72.5a

68.0ac

55.5bc

47.0b

44.0b

46.4


12.0b

16.0a

12.5b

13.5



13.0b

20.5a

4.5c

2.5d

2.5d

3.5c

7.8










Table 4.4. Tissue chemical composition of evenia leaves and stems in year 2001.


P Ca K Mg
g kg-'


Leaves

Sep

Oct

Nov

Mean

Stems

Sep

Oct

Nov

Mean


9.3a

5.4a

6.9a

7.2



4.9a

3.9a

4.5a

4.4


15.0a

16.2a

14.7a

15.3



9.6a

10.7a

8.8a

9.7


3.8a

2.3b

2.7c

2.9



1.3a

1.la

1.4a

1.3


Zn Mn


48.5a

49.5a

43.5a

47.2



42.5a

41.0a

33.0a

38.8


mg kg'_


213.0a

186.5a

159.0a

186.2



59.5a

84.0a

37.5a

60.3


Fe Cu


62.5a

63.0a

87.0a

70.8



24.0b

39.0b

72.5

45.2


19.0a

13.5b

13.0b

15.2



23.0a

19.5a

12.5b

18.3


* Means within a column and plant section followed by different letters are different by
PDIFF (P<0.05)


3.0a *

3.5a

3.4a

3.3



2.1a

2.4a

2.3a

2.3









Table 4.5. Tissue chemical composition of creeping vigna in year 2002


Month P Ca K Mg Zn Mn Fe Cu
g kg-1 mg kg-'
g kgg

May 1.6b 12.6a 13.0b 3.7a 27.0b 95.5a 109.5a 8.5b

Jul 4.0a 10.4a 26.5a 4.9a 51.5a 90.0a 151.0a 19.0b

Aug 3.8a 7.7b 22.9a 4.8a 36bc 49.5a 121.5a 18.5b

Sep 3.7a 8.0b 16.8b 4.9a 40.5ac 56.0a 113.0a 30.5ab

Oct 3.8a 6.8b 15.5b 3.5a 50.0a 70.0a 92.5a 17.5b

Mean 3.4 9.1 18.9 4.4 41.0 72.2 117.5 18.8

* Means within a column followed by different lower case letters are different by PDIFF
(P<0.05)














CHAPTER 5
SUMMARY AND CONCLUSIONS

A grazing trial was conducted at the Range Cattle Research and Education Center,

Ona of the University of Florida, from September to December 2001 and May to

November in 2002 to 1) measure forage availability and nutritive value and 2) to

determine comparative growth responses of yearling cattle to variably-stocked,

continuously grazed evenia-bahiagrass, Shaw creeping vigna-bahiagrass, and pure

bahiagrass pastures.

The variables measured were: herbage mass, in vitro organic matter digestibility

(IVOMD), crude protein (CP), tissue chemical composition, average daily gain (ADG),

and gain per hectare. Pasture botanical composition was also measured.

From the results of this experiment, we came to the following conclusions.

The contribution of legumes in both years was low. A disadvantage of legumes is

their slow establishment, and in the present study this happened especially with creeping

vigna that did not establish in 2001.

Herbage mass of the bahiagrass component was not different between pasture

treatments in 2001 (4150 kg ha-') and 2002 (2720 kg h-), but it did change during the

grazing season. Herbage mass of the bahiagrass component was low in 2002 because

grazing started early, which prevented early season HM accumulation.

Crude protein and IVOMD of the bahiagrass component were the same for all

pasture treatments. Nutritive value of the bahiagrass component changed during the

grazing season. Herbage CP and IVOMD of the bahiagrass component were generally









below the average values expected for bahiagrass because no N fertilizer was applied and

legume contribution to the system was poor.

Evenia leaves had a greater nutritive value than the stems and creeping vigna plants

had a greater nutritive value than evenia plants. More evenia forage was produced in

2001 compare with 2002. It was suspected that animals did not eat much creeping vigna

in 2002 because calves were too young and unaccustomed to it.

Animal performance (seasonal ADG and gain per hectare) was not different among

pasture treatments. The low animal performance was a result of the low bahiagrass

quality and low content of legumes in the system. Overall, forage quality was not able to

cover the nutritional needs of young steers in late season. The inclusion of a legume in

bahiagrass pastures did not improve overall nutritive value of the pasture sufficiently to

sustain good steer performance.















APPENDIX

Table A.1. Herbage mass (kg ha') of the bahiagrass component for pasture treatments by
month in 2001.

Treatments


Month


Sep

Oct

Nov

Mean


Evenia-bahiagrass


Bahiagrass


4300

4990

3990

4420


Mean


3720

4810

3110

3880


4010

4900

3550

4150


Table A.2. Herbage mass (kg ha') of the bahiagrass component for pasture treatments by
month in 2002.


Evenia-bahiagrass


2630

1550

2190

3130

3090

2340

2490


Treatments
Creeping vigna-bahiagrass


3040

1780

2070

3470

3830

2910

2850


Month


May

Jun

Jul

Aug

Sep

Oct

Mean


Bahiagrass


3290

1810

1820

2840

3030

2380

2530


Mean


2990

1710

2030

3150

3320

2540

2620










Table A.3. Mean CP (g kg-') of the bahiagrass component for pasture treatments by
month in 2001.

Treatments


Month


Sep

Oct

Nov

Mean


Evenia-bahiagrass


Bahiagrass


Mean


Table A.4. Mean CP (g kg-') concentration of the bahiagrass component for pasture
treatments by month in 2002.


Evenia-bahiagrass


77

95

95

75

67

73

80


Treatments
Creeping vigna-bahiagrass


69

76

79

75

64

65

71


Mean


Month


May

Jun

Jul

Aug

Sep

Oct

Mean


Bahiagrass


74

88

99

75

75

74

81









Table A.5. Seasonal changes in (CP g kg-) concentration in evenia and creeping vigna
plants in 2002


Month Evenia Creeping vigna


May 198

Jun 172 140

Jul 149 253

Aug 161 196

Sep 186 173

Oct 141 198

Mean 162 193

* No data is reported for evenia in May 2002 because evenia was not present in samples
collected.









Table A.6. In vitro organic matter digestibility (g kg-) of the bahiagrass component for
treatments and month in 2002.

Treatments
Month Evenia-bahiagrass Creeping vigna-bahiagrass Bahiagrass Mean


May 423 389 391 401 b*

Jun 388 346 402 379c

Jul 469 404 459 444 a

Aug 424 408 425 419b

Sep 429 406 431 422b

Oct 385 336 359 360 c

Mean 419 381 411 404

* Means within a column with different superscripts are different by PDIFF (P<0.05)



Table A.7. In vitro organic matter digestibility (g kg-') of evenia stems (> 3 mm) in
2001.


Month Stems


Sep 277

Oct 218

Nov 226

Mean 240









Table A.8. Seasonal changes on IVOMD (g kg-') of evenia and creeping vigna plants in
2002.

Month Evenia Creeping vigna


May ---- 700

June 577 631

July 481 667

Aug. 465 657

Sept. 598 688

Oct. 563 726

Mean 537 678










Table A.9. Tissue chemical composition of the bahiagrass component for treatments in
2001 and 2002.


P Ca
g kg-1


K Mg


Zn Mn Fe
mg kg1_


2001


Evenia-bahiagrass 2.1 2.3 8.6 3.9 22.0

Bahiagrass 1.9 2.2 7.7 4.0 21.5

Mean 2.0 2.3 8.2 3.9 21.8

2002

Evenia-bahiagrass 2.7 2.7 13.9 2.6 24.5

Creeping vigna- 2.3 2.8 13.3 2.5 21.5
bahiagrass
Bahiagrass 2.7 2.8 13.6 2.6 24.5

Mean 2.6 2.8 13.6 2.6 23.5







Table A. 10. Tissue chemical composition of evenia in 2002.


128.5

159.0

158.8



72.0

65.5

74.5

70.7


123.0

45.5

84.2



55.5

60.5

54.0

56.7


P Ca K
g kg-1

3.5 5.0 14.5

4.0 7.1 14.4

3.8 5.1 11.0

3.8 5.7 13.3


Mg


1.9

3.2

2.1

2.4


Zn


36.5

45.0

37.5

39.7


Mn Fe
mg kg-'

44.5 57.5

84.5 80.0

49.0 44.5

56.7 61.7


12.5

14.5

13.5



8.0

7.0

8.0

7.7


Month


Aug

Sep

Oct

Mean


Cu


11.0

10.5

10.5

10.7












Table A. 11. Monthly HM, SR, and cumulative ADG with a variable herbage allowance in 2001.


Herbage allowance
kg DM (100 kg BW ha)-' d-


Calculated SR
kg BW ha-


Applied SR Cumulative ADG
kg BW ha- kg d-


Sept.

Evenia-bahiagrass

Bahiagrass

Oct.

Evenia-bahiagrass

Bahiagrass

Nov.

Evenia-bahiagrass

Bahiagrass


Month


HM
kg ha-'


4580

3720



5270

4820



3980

3120


1020

830


1090

1000


910

780



1000

930



1010

935


0.84

0.82



0.53

0.47



0.09

0.16


1327

1040












Table A. 12. Monthly total HM, herbage accumulation (HA), SR, and cumulative ADG with a constant herbage allowance of 10 kg
DM (100 kg BW)- d' for evenia-bahiagrass (EB), creeping vigna-bahiagrass (CVB) and pure bahiagrass (B) pastures in
2002.


Calculated SR
kg BW ha-


1013

1100


755


Applied SR
kg BW ha-


700

775

880


750

840

880


HM
kg ha-'


2630

3040

3290


1550

1780

1810


2190

2100

1820


620

620


Cumulative ADG
kg d-


0.51

0.64

0.67


0.42

0.37

0.45


0.31

0.21

0.28


* No HM data reported since grazing season started in May and no herbage accumulation data was available at that time.


SR for HM
kg BW ha-


HA
kg ha-'


SR for HA
kg BW ha-'


880


Month


May
EB


CVB


June
EB

CVB


July
EB

CVB


1055

1010


1013

1100


517

593

603


730


/

/


712

372

712


970

930


/

/


237

124

104


325

310

270


700

605













Table A. 12. continued


Calculated SR
kg BW ha-


Applied SR
kg BW ha-


Month


Aug.
EB

CVB

B

Sept.
EB

CVB

B

Oct.
EB

CVB

B


SR for HM
kg BW ha-


HA
kg ha-'


SR for HA
kg BW ha-


HM
kg ha-'


3130

3480

2840


3090

3830

3030


2340

2910

2380


700

620

620


825

685

660


800

660

630


Cumulative ADG
kg d-


0.21

0.16

0.12


0.12

0.04

0.03


0.09

-0.04

-0.10


1710

970

1380


1340

1020

880


350

390

320


515

640

505


780

970

795


570

325

460


450

340

295


80

7

115













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BIOGRAPHICAL SKETCH

Maria Yolanda Castelo Ipiales was born September 12, 1976 in Quito, Pichincha

province, Ecuador. She graduated from Colegio Frances High School, Quito, Ecuador in

1994. From January 1995 to May 1999, she attended the Escuela Agricola Panamericana,

El Zamorano, in Honduras; and received the Ingeniero Agronomo degree with a major in

plant protection. From January 2000 to June 2001 she participated in the Minnesota

Agricultural Student Trainee (MAST) program from the University of Minnesota.

She entered graduate school at the University of Florida in August 2001. She is a

candidate for the Master of Science degree, with a major in agronomy and a minor in

agricultural education and communication.