Grazing Tolerance Research Articles

Persistence of Perennial Cool‐Season Grass and Legume Cultivars under Continuous Grazing by Beef Cattle

Persistence of highly productive forage species in pastures is essential to maximize economic returns from grazing livestock. However, most forage cultivars are neither developed nor evaluated under grazing. The objective of this study was to evaluate several cool‐season forage species and cultivars to determine their tolerance to continuous grazing. Three grazing experiments were established in 1996 in central Iowa: (i) 20 cultivars and populations of alfalfa (Medicago sativa L.), (ii) 15 cultivars representing five cool‐season legume species, and (iii) 25 cultivars and germplasms of six cool‐season grass species. Beef cattle (Bos taurus) continuously grazed the experiments for about four months in 1997 and 1998. Alfalfa yield was measured in adjacent plots. Stand survival ratings were taken each year. Among the alfalfa entries, grazing‐tolerant ‘Alfagraze’ showed high persistence but moderate yield. Several new alfalfa populations combined excellent grazing tolerance with yield equal to the best hay‐type cultivar. Kura clover (Trifolium ambiguum Bieb.) and white clover (T. repens L.) persisted better than alfalfa, birdsfoot trefoil (Lotus corniculatus L.), and red clover (T. pratense L.), with no loss of stand after two grazing years. Orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.) persisted well, though considerable variation was present among orchardgrass cultivars after the second grazing year. Reed canarygrass (Phalaris arundinacea L.) and smooth bromegrass (Bromus inermis Leyss.) stands were reduced to <10% after one grazing year. Although the severe, continuous grazing used in these experiments is not recommended, it clearly and quickly differentiates among species and cultivars for grazing tolerance.

Carbon allocation in Euphorbia esula and neighbours after defoliation

Weeds increase their dominance in a grazed plant community by avoiding herbivory and (or) by tolerating herbivory more than neighbouring plants. After defoliation, allocating carbon to shoots at the expense of roots may confer tolerance. We determined carbon allocation patterns of undefoliated and recently defoliated (75% clipping level) plants of the invasive leafy spurge (Euphorbia esula L.) growing with alfalfa (Medicago sativa L.), Kentucky bluegrass (Poa pratensis L.), or Idaho fescue (Festuca idahoensis Elmer). Plants were labeled with 13CO2 24 h after clipping to determine allocation patterns; all plants had equal access to the 13CO2. Based on relative distribution of 13C, defoliation did not affect the amount of carbon allocated to roots of E. esula. The amount of carbon allocated to shoots of E. esula was higher when growing with P. pratensis than when growing with the other species. Based on relative enrichment of 13C, defoliation increased sink strength of remaining shoots on defoliated E. esula plants. Conversely, roots of unclipped E. esula plants were stronger sinks for carbon than roots of clipped plants. Even though defoliation increased "sink strength" of remaining shoots of E. esula, the amount of carbon allocated to the root system was unaffected by defoliation, suggesting that uninterrupted allocation of carbon to its extensive root system, not increased allocation to its shoot system, confers grazing tolerance.

Seed production in sideoats grama populations with different grazing histories

Frequent and intense defoliation of grasses has been associated with the evolution of "grazing morphotypes" that exhibit a variety of vegetative traits correlated with improved grazing resistance. While recovery from a seed bank is not considered an important grazing resistance mechanism, relatively little is actually known regarding seed (caryopsis) production in grazing morphotypes of caespitose grasses. The goal of this research was to compare components of seed production in 2 populations of sideoats grama (Bouteloua curtipendula var. caespitosa Gould Kapadia) from nearby sites with different histories of livestock grazing. This was done using vegetative propagules of genotypes from both populations in a greenhouse study. The study was conducted in 2 flowering seasons under conditions considered favorable for seed production. The population exposed to livestock grazing showed a genetically based decrease in seed production relative to the ungrazed population. Lower seed production per plant in the grazed population was at least partially due to reduced numbers of tillers and panicles per plant and spikes per panicle that may be associated with selection for grazing tolerance. The grazed population also exhibited lower average seed production per spike indicating lower inherent floral fertility. Seed production was not closely correlated with vegetative traits associated with increased grazing tolerance, nor was there evidence of obvious physiological trade-offs related to decreased seed production in the grazed population. Lower seed production potential in populations of sideoats grama intensively grazed by livestock may lead to reduced potential for seedling colonization.

Persistence and Yield among Nondormant Alfalfas Selected for Grazing Tolerance

Perennial, warm season grasses are the predominant pasture species in the Coastal Plain of the southern USA. These grasses have two major limitations: (i) an off-season (normally winter) when they have either limited or no production and (ii) low nutritional value during most of their main growing season. Using nondormant alfalfa (Medicago sativa L.) as supplemental grazing for grass pastures may overcome these limitations because it has a long growing season in areas with mild winters and also has high nutritional quality. However, alfalfa is generally not grazed due to poor stand persistence and grazing-tolerant cultivars are currently dormant types. Therefore, we used selection for survival after heavy grazing pressure with continuous stocking by beef cattle (Bos sp.) to develop two nondormant, grazing tolerant alfalfa germplasms. These were then tested for survival and forage yield in four experiments of 1 to 2 yr duration under heavy grazing pressure with continuous stocking by beef cattle at Tifton, GA. The selected, nondormant alfalfa germplasms persisted under heavy grazing pressure as well as the grazing tolerant, dormant cultivar, Alfagraze, but were better in respect to plant survival than other nondormant cultivar checks. All entries survived in control areas that were clipped at an early flowering stage. The yield of nondormant cultivars was better from late autumn through early spring than Alfagraze. Some winter damage occurred in 1 of the 4 yr for the nondormant germplasms and cultivars, which did not occur with Alfagraze.

Cool‐Season annual legume effects on wheat forage nutritive value

Hard red winter wheat (Triticum aestivum L. emend. Thell.) is an important cool‐season winter forage used primarily for increasing weight gain on growing beef cattle in the southern Great Plains. ‘Karl’ hard red winter wheat grown alone or grown with either hairy vetch (Vicia villosa Roth) or pea [(Pisum sativum L. subsp. arvense) var. ‘Austrian winter'] was sampled for forage nutritive value. The interplanted legume forage was also sampled for forage nutritive value. Ruminally degradable nitrogen (RDN):ruminally degradable organic matter (RDOM) ratios were highest for legume forage and exceeded the National Research Council (NRC) recommendation of 26.13 g RDN: 1 kg RDOM for peak ruminai microbial efficiency during March, April, and May sample periods over the 2‐year study. Wheat grown alone met the NRC requirement only during March. Wheat grown with either hairy vetch or pea had higher (P<0.05) RDN:RDOM ratios and crude protein (CP) values when compared to wheat grown alone during May. There were no differences (P>0.05) in dry matter (DM) yield between wheat grown alone or grown with the legumes except when analyzed by individual date, and then only for 1 of 6 sample dates. Undegraded intake protein (UIP) was generally higher (PO.05) for wheat compared to the legumes and higher (PO.05) for wheat grown alone during May compared to wheat grown with the legumes during May. The decline of the RDN:RDOM values to 40% below the NRC recommendation of wheat grown alone during May indicates a possible need for protein supplementation for growing beef cattle grazing wheat during this period. These data also indicate that interplanting legumes with wheat may enhance animal performance by providing forage of higher nutritive value. More information regarding grazing tolerance of these selected cool‐season annual legumes and subsequent animal performance is required.

Length and Timing of Grazing on Postburn Productivity of Two Bunchgrasses in an Idaho Experimental Range

Plant mortality and productivity in semiarid grasslands may be affected by the length of time grazing is excluded during the postfire regeneration period. The degree of grazing tolerance for the semiarid bunchgrass species, Festuca idahoensis and Agropyron spicatum, exposed to fire, and how the variation in grazing tolerance was affected by the length of time allowed for undisturbed plant regeneration after fire, were central questions addressed in this study. We examined the degree of plant mortality and productivity that resulted from the interaction of fire and grazing. Plants exposed to fire alone, i.e., without subsequent defoliation, exhibited low plant mortality, although culm production was reduced relative to unburned plants. An early-season-defoliation treatment after fire resulted in the plant mortality as high as 50% for Festuca and 70% for Agropyron bunchgrasses. Plant height and the number of vegetative and reproductive culms were also most affected by this defoliation treatment. These detrimental effects were lessened when defoliation was delayed by one growing season after the fire. Although our results suggest that one growing season seems to be enough for both species to recover after the fire, more studies will be necessary to confirm these trends, and induce changes in current grazing management policies.

Defoliation Tolerance of Bluebunch and Snake River Wheatgrasses

AbstractBluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Löve] has long been noted for poor tolerance to grazing during culm elongation in the spring. Bluebunch wheatgrass is an autoploid series of diploids (2x) and tetraploids (4x). In the mid‐1980s, a group of populations were found to be allotetraploid and are now commonly referred to as Snake River wheatgrass. Relative grazing tolerance of 2x and 4x bluebunch wheatgrass and of Snake River wheatgrass is unknown. This study evaluated the effect of multiple defoliation on these grasses to simulate one consequence of grazing, removal of photosynthetic tissue. Fifteen entries representing the three taxa were established at North Logan, UT, on a Millville silt loam (coarse‐silty, carbonatic, mesic Typic Rendolls; 2–4% slope) during 1988. Seedlings were vegetatively propagated into two clones apiece and transplanted adjacent to one another; one clone was subjected to multiple defoliation and the other served as an undefoliated control. Multiple defoliation at 10 cm was applied from late spring to midsummer from 1990 to 1992 at 4‐wk intervals and dry matter yield was measured in late fall 1991, early spring 1992, late fall 1992, and late spring 1993. We used the defoliated‐to‐control ratio of plant response to estimate defoliation tolerance. The defoliated‐to‐control ratio for dry matter yield of Snake River wheatgrass (0.17 and 0.38 in late fall 1991 and early spring 1992, respectively) was greater than for 4x (0.06 and 0.18) or 2x (0.06 and 0.19) bluebunch wheatgrasses after the first year of multiple defoliation. The defoliated‐to‐control ratio for dry matter yield did not differ among taxa in late fall 1992, but the ratios for Snake River wheatgrass (0.20) and 4x bluebunch wheatgrass (0.21) were both greater than for 2x bluebunch wheatgrass (0.13) in late spring 1993. Less variation was seen among Snake River than bluebunch wheatgrass entries. Because Snake River wheatgrass had both higher yield and greater defoliation tolerance than bluebunch wheatgrass, Snake River wheatgrass is more likely to survive defoliation over the long term.

Flowering of Berseem Clover Types in Response to Vernalization

Winter hardiness of ‘Bigbee’ berseem clover (Trifolium alexandrinum L.) was reported to differ between plants grown from certified seed and breeder seed. Winter growth form also differed, with plants from breeder seed forming a rosette and plants from certified seed elongating. To determine if growth form differences were due to a change in vernalization response, imbibed seeds of Bigbee certified and breeder seed and certified ‘Multicut’ were vernalized at 2°C for 0 to 6 wk in weekly increments. Seeds from all treatments were simultaneously germinated and grown in a greenhouse under 18‐h daylength. Days to flowering, node at first flower, and the number of nodes below 5 cm at flowering were recorded. Replicated experiments were conducted with germination dates of 17 Aug. 1992 and 25 Feb. 1993. The regression of days to flowering and node at first flower on vernalization period was significant for Bigbee certified and breeder seed. Response slopes of Bigbee plants grown from certified and breeder seed differed from each other for all variables. As vernalization period decreased, plants from Bigbee breeder seed flowered later and at a higher node than plants from Bigbee certified seed. Vernalization had no effect on days to flowering or node at first flower for Multicut. Variation in vernalization response between Bigbee breeder seed and certified seed indicated that a change occurred during the production of certified seed. Multicut and Bigbee certified seed may have less winter grazing tolerance than Bigbee breeder seed since there were fewer nodes near the soil line to support regrowth.

Evaluation of a lucerne germplasm collection in relation to traits conferring grazing tolerance

A collection of 90 accessions of different germplasm groups from the Medicago sativa complex was evaluated at Lodi, Italy, for dry-matter yield, time to anthesis, height of regrowth, plant diameter, stem density, vegetative recovery after winter, and presence of deep-set crown and ability to spread with creeping roots or rhizomes, these latter characters possibly contributing to grazing tolerance. The germplasm groups proved rather distinct for these traits, but all included types potentially suitable for grazing. Interesting types combining deep-set crown and high yield occurred mainly in subsp. x varia and materials originated from artificial crosses involving at various extent the subspecies falcata, sativa and x varia. Though belonging to subsp. sativa, “mielga” wild populations from Spain had aerial traits similar to those of the long-dormant, low-yielding subsp. falcata. Deep-crowned plants had greater plant diameter than shallow-crowned plants, and could be categorised into four distinct top-growth models according to their habit and vigour. One of these models combined spreading ability with high yield. The about 150 plants selected for their combination of deep crown, wide diameter, and good yield were characterised by a branch-rooted system. There was general correspondence between top-growth and root morphology of each model. Of the four deep-crowned models, three had rhizomes, with wide range of underground development and morphology, while the fourth had creeping roots. The latter model was the most rare among the examined accessions, never appearing in either cultivated or wild subsp. sativa. The implications of the results on the development of grazing-tolerant lucerne varieties are discussed.

Breeding white clover for tolerance to low temperature and grazing stress

Low temperature and grazing are the two major stresses limiting white clover yield in mixed swards grown in the marginal areas of the UK. White clover has traditionally been used to improve productivity in such areas but is increasingly being used to reduce input costs in more productive areas. Considerable genetic variation exists in characters associated with cold tolerance, low temperature growth and grazing tolerance. This paper describes recent progress in developing varieties tolerant to three major stresses and which give greater and more reliable production.

Persistence of cool-season grasses under grazing using the mob-grazing technique

Evaluation of grass germplasms for pasture is usually done in trials which are harvested mechanically. This study evaluated the persistence of 13 cool-season grass species and germplasms under 4 yr of grazing in northeast Saskatchewan, using the mob-grazing technique. Thirteen grass germplasms were contained within each paddock, and the paddocks were grazed by large groups of cattle so that all the herbage was consumed evenly in 1–2 d. Three grazing intensities (light, moderate and intense) were established by varying the rest period between grazings. Ground cover declined more rapidly under intense than under light grazing, but no interaction was found between grazing intensity and grass germplasm. The ground cover of the seeded grasses generally declined but at different rates during the trial, giving a significant grass × year interaction. Parkway crested wheatgrass [Agropyron cristatum (L.) Beauv. ssp. pectination (Bieb.) Tzvel.] declined less than Carlton smooth bromegrass (Bromus inermis Leyss.) and the meadow bromegrass (Bromus biebersteinii Roem &amp; Schult.) cultivars. The most rapid stand decline was observed in intermediate wheatgrass [Elytrigia intermedia (Host) Nevski], northern wheatgrass (Elymus lanceoiatus Scribn. &amp; Smith), and hybrid wheatgrass [Elytrigia repens (L.) Nevski × E. spicata (Pursh) D. R. Dewey]. Seeded grasses were replaced mainly by bluegrass (Poa spp.). The results suggest that mob grazing is a useful technique for evaluating new species and germplasms intended for long-term pastures. Key words: Grazing tolerance, temperate grasses, pasture, ground cover, bromegrass, wheatgrass, wildrye, bluegrass

Evaluating alfalfa cultivars and germplasms for pastures using the mob-grazing technique

There is growing evidence that alfalfa (Medicago sativa L. sensu lato) germplasms that perform well in trials that are mechanically clipped may not persist well under grazing. This trial assessed the persistence of nine alfalfa germplasms under grazing over a period of 4 yr in northeast Saskatchewan. The germplasms included registered cultivars and experimental strains of M. sativa ssp. media Pers. and M. sativa ssp. falcata (L.) Arcang. with a range of growth habits and winterhardiness. Each paddock was seeded with all entries in mixture with smooth bromegrass (Bromus inermis Leyss.) and grazed repeatedly for 1- to 2-d periods, using high stocking rates, to ensure that all entries were grazed uniformly. Three grazing intensities — light, moderate and intense — were set by varying the rest period between grazings. Ground cover of all the currently recommended alfalfa cultivars of the media ssp. declined during the trial; the germplasms of falcata ssp. increased; and two media ssp. strains from northern Alberta maintained fairly constant ground cover. Grazing intensity affected rate of stand decline but not final ranking of germplasms, so there was no grazing × germplasm interaction. Seeded and volunteer smooth bromegrass maintained better stands under light than intense grazing, whereas volunteer bluegrass (Poa spp.) performed better under intense grazing. Ground cover of alfalfa germplasms was generally correlated with their annual yield and proportion of total dry matter yield. The results suggest that falcata germplasms should be included in seed mixes for long-term pastures and that mob grazing be used to assess the persistence of alfalfa germplasms before they are recommended for use in pastures. Key words:Medicago sativa L., Medicago sativa ssp. falcata (L.) Arcang., persistence, grazing tolerance.

Persistence of Idaho Fescue on Degraded Rangelands: Adaptation to Defoliation or Tolerance

Rangelands with histories of overgrazing are frequently depauperate of native grasses. Occasionally, remnant native grasses are found surviving in these areas. We hypothesized that these survivors have responded to livestock grazing, over the past 110 years, through development of genetically based ecotypes that are more tolerant of defoliation than populations protected from heavy use by domestic livestock. Transplanted individuals of a native grass, Idaho fescue (Festuca idahoensis Elmer), from heavily grazed and ungrazed rangelands were compared. Gardens were established in central Oregon at the Central Oregon Agricultural Experiment Station and in eastern Oregon at the Northern Great Basin Experimental Range. Plants were defoliated during the vegetative, boot, and anthesis stages in 1990 and 1991 and subsequent growth evaluated. Parameters measured were end of growing season basal area, relative biomass production, and height and phenology at about biweekly intervals. Grazing history had no consistent effect on Idaho fescue response to defoliation. There were, however, differences between the protected and grazed collections from central Oregon in that the protected population averaged greater height and relative growth than those from the grazed areas even with defoliation. While the limited number of ungrazed sources in this region limits broad speculation, these results suggest idaho fescue survival in heavily grazed areas might be the result of differences in growth form rather than overcompensation or variation in time of phenologic development. Results also suggest that Idaho fescue from this region may elicit some grazing tolerance despite evolving historically with few large herbivores.

Selection within Alfalfa Cultivars for Persistence under Continous Stocking

Alfalfa (Medicago saliva L.) has been predominately used as a hay crop in North America and most cultivars do not persist under grazing. The objectives of this research were to determine if grazing tolerance could be improved within alfalfa cultivars and to determine population shifts that occurred during selection. The original and selected populations of ‘Apollo’, ‘Florida 77’, ‘Alfagraze’, ‘Spredor II’, and ‘Travels’ were evaluated in central Georgia under 17 to 22 wk of continuous close grazing by beef cattle for 2 yr. Experiments I and II were comprised of two seasons of continuous close grazing and Exp. Ill was comprised of two seasons management for hay production. In addition, eight released, multiple‐pest‐resistant cultivars were also evaluated in Exp. II and III. Stand persistence was measured with plant density measurements and forage production was measured under exclosures. All selected populations, with the exception of Alfagraze, had better stand persistence and yield than their original populations when grazed, but yield and persistence were similar when managed for hay production. Although several fungal pathogens influenced plant mortality there was an inconsistent relationship between disease resistance and stand persistence under grazing. This research indicated that at least two seasons of continuous grazing are required to achieve a consistent ranking for grazing tolerance. In conclusion, this study suggests that grazing tolerance can be improved within existing cultivars without sacrificing forage yield.

Spring‐Clipping Response in Snake River and Thickspike Wheatgrasses

AbstractGrazing at the boot stage can severely damage stands of bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Löve]. Snake River wheatgrass [proposed name Etymus lanceolatus ssp. wawawaiensis (Scribner &amp; Gould) J.R. Carlson &amp; D.R. Dewey] has recently been recognized as a taxon distinct from bluebunch wheatgrass, based on cytological data, and placed in the same species as thickspike wheatgrass [Elymus lanceolatus ssp.lanceolatus (Scribner &amp; J.G. Smith) Gould]. Grazing tolerance of Snake River wheatgrass is unknown. This study was conducted to evaluate the effect of clipping at the boot stage on vigor of ‘Secar’ Snake River wheatgrass, ‘Elbee’ and T‐21076 thickspike wheatgrass, and hybrid populations D30 (50% Snake River wheatgrass/50% thickspike wheatgrass) and D38 (75% Snake River wheatgrass/25% thickspike wheatgrass). Plots were established at North Logan, UT (mollisol) and near Stone, ID (aridisol) in 1987, clipping treatments (clipped or unclipped at the boot stage) were applied in 1988 and 1989, and treatments were compared in 1990. Regardless of spring‐clipping treatment, all plants were clipped once in the summer at both locations and again in the fall at North Logan both in 1988 and 1989. Spring clipping reduced Secar dry weight 21%, spike number 27%, and plant basal area (above‐ground area occupied by tillers) 17% at North Logan, while the other populations were unaffected. Spring clipping reducedry weight 26 and 31%, spike number 37 and 36%, and plant basal area 24 and 33%, of Secar and D38, respectively, near Stone, while the other populations were unaffected. Spring clipping was more detrimental at the Stone aridisol than the North Logan mollisol site. Currently available germplasm of the rhizomatous thickspike wheatgrass appears to be more tolerant of spring clipping than that of the caespitose Snake River wheatgrass. It should be possible to make substantial genetic progress for spring‐clipping tolerance in hybrid populations.

Defoliation effects on resource allocation in Arizona cottontop (Digitaria californica) and Lehmann lovegrass (Eragrostis lehmanniana)

Arizona cottontop (Digitaria californica), a bunchgrass native to the Chihuahuan and Sonoran Deserts in North America, and Lehmann lovegrass (Eragrostis lehmanniana), a bunchgrass introduced to the southwestern USA from southern Africa, were defoliated and examined for above‐ and below‐ground productivity, nitrogen and phosphorus allocation, and photosynthetic potential. Stems plus sheaths from which leaf blades have been removed may be important to Lehmann lovegrass because this tissue is photosynthetically active and contains nitrogen and phosphorus reserves. After defoliation, Arizona cottontop re‐established a canopy more quickly than Lehmann lovegrass but differences were due to greater numbers and growth rates of Arizona cottontop leaves. Rapid Arizona cottontop leaf growth was followed by a 50% decline in below‐ground biomass. Lehmann lovegrass had a lower investment in above‐ and below‐ground biomass, nitrogen and phosphorus per plant. Grazing tolerance associated with Lehmann lovegrass may be rel...

Physiological Traits Associated with Grazing‐Tolerant Alfalfa

AbstractMany alfalfa (Medicago sativa L.) cultivars do not persist under long‐term, continuous grazing. This study was conducted to examine the variation of physiological traits that may contribute to grazing tolerance. Plants of the grazing‐tolerant cultivars Alfagraze and Travois and the grazing‐intolerant cultivar Florida 77 were grown from seed (Study 1) and from cuttings (Study 2) in the greenhouse. Populations from each cultivar that survived 2 yr of continuous grazing in the field were also tested in Study 2. Plants were clipped either frequently (weekly) or infrequently (every 4 wk) for 20 wk. Measurements of root total nonstructural carbohydrates (TNC), root weight, top and stubble herbage yield, and stubble leaf area were taken at Weeks 0, 2, 4, 10, 12, 18, and 20. No differences were noted between populations in Study 2. Under infrequent clipping TNC levels for all cultivars were higher at 4 than 2 wk after clipping. Florida 77 produced high TNC and root and top weights only under infrequent clipping but had low TNC and root weights under both clipping regimes, produced low top and stubble herbage dry matter, but maintained high stubble leaf areas under frequent clipping. Alfagraze produced and maintained high TNC and root weights under both clipping treatments, but produced high stubble dry matter and leaf area under frequent clipping. The genetic potential of a cultivar to store large amounts of carbohydrates may enhance its grazing tolerance, although stubble leaf area is probably important in allowing maintenance of total nonstructural carbohydrates under frequent defoliation.

Plant Traits Associated with Grazing‐Tolerant Alfalfa

AbstractMost alfalfa (Medicago sativa L.) cultivars cannot withstand longterm, continuous grazing. This study was conducted to determine if plant morphological traits differ among alfalfa cultivars and populations that vary in persistence under grazing stress. Hay‐type cultivars (Apollo and Florida 77), grazing‐type cultivars (Spredor II, Travois, and Alfagraze), and populations derived from these cultivars that survived continuous grazing for l or 2 yr were space‐planted in the field in 1987 and 1988. Plants were clipped biweekly for 16 wk. Decumbency, stem number and diameter, crown area, and herbage yield were measured at five 4‐wk intervals (Dates 1‐5). Crown buds were counted in the fall. Original populations from Spredor II and Travois had thinner stems, more decumbent growth, lower herbage yield, and more stems (at Date 1) when compared with populations from Florida 77 and Apollo. Alfagraze had many, thick stems, intermediate decumbency, and high herbage yield, indicating these traits can be realized along with grazing tolerance. Alfagraze and Travois had the most crown buds. Selected plants of some cultivars had fewer stems and more decumbent growth initially, but differed little from their original populations for these traits after 120 d of frequent clipping. Year‐2 selections from Sprdor II and Florida 77 had more crown buds than their original populations. Genetic coefficients of variation suggested that selection had resutled in little reduction in genetic variation and that further selection for all traits may be possible in each cultivar.

Grazing Tolerance of Warm‐Season Legumes in Peninsular Florida

AbstractDespite the potential benefits and frequent favorable results in germplasm evaluations, only limited success has been attained in many areas with tropical pasture legumes. Lack of information regarding both germplasm adaptation and pasture management requirements has been a limitation. Five promising perennial species were evaluated for grazing tolerance and response to fall grazing deferment on an Immokalee fine sand (Sandy, siliceous, hyperthermic Arenic Haplaquod) at Ona, FL. Alysicarpus vaginalis DC; Desmanthus virgatus (L.) Willd.; Galactia elliottii Nuttall; G. volubilis (L.) Britton; Vigna adenantha (G. F. Meyer) Marechal, Mascherpa, and Stainier; and the standard ‘Florida’ carpon desmodium [Desmodium heterocarpon (L.) DC] were subjected to three treatments: (i) continuous grazing through the growing season (late May to mid‐December), (ii) continuous grazing with fall deferment (grazed late May to mid‐September), and (iii) an ungrazed control. Legume main plots, 5 by 15 m in a randomized complete block design, were split in a strip‐plot arrangement to give grazing treatment subplots of 5 by 5 m. Legumes were transplanted in 1986, grazed in 1987 and 1988, and evaluated for persistence through the summer of 1989. By December 1988, the prostrate A. vaginalis had the highest (P &lt; 0.05) survival percentage under both grazed treatments. Survival of D. virgatus, G. elliottii, and V. adenantha was generally highest in the ungrazed control. The Galactia species demonstrated superior adaptation to drought during the spring of 1989. Fall deferment consistently increased survival of only G. volubilis and V. adenantha. Tolerance of continuous grazing was suggested only for A. vaginalis and carpon desmodium. Grazing management strategies involving periods of deferment from grazing during the growing season will apparently be necessary for persistence of stands of D. virgatus and G. elliottii.

Alfalfa Persistence and Regrowth Potential under Continuous Grazing

AbstractAlfalfa (Medicago saliva L.) generally does not persist well under continuous grazing. Experiments were conducted under continuous grazing to compare the persistence and regrowth potential of an alfalfa germplasm (Georgia—Grazed Collection, GA‐GC), selected for continuous grazing, with two hay‐type (Apollo and Florida 77) and two grazing‐type (Travois and Spredor II) cultivars. The germplasm and cultivars were subjected to continuous, heavy grazing by beef cattle for 18 weeks in each of 3 yr to a height of 3 to 5 cm. Wire exclosures rotated at 28‐d intervals on all plots were used to estimate the regrowth potential of each entry during the grazing period. Plant and stem counts were taken before and after grazing each year as estimates of stand persistence. Cultivars differed significantly for stand persistence after 3 yr of continuous grazing with 6 to 9 plants m−2 remaining for the hay‐type cultivars and 40 to 48 plants m−2 remaining for grazing‐type cultivars. The GA‐GC maintained plant densities of 64 plants m−2 while producing the highest forage regrowth compared with all cultivars. Total nonstructural carbohydrates (TNC) in roots at the end of 1986 and 1987 grazing seasons ranged from 256 g kg−1 for Florida 77 to 429 g kg−1 for Travois, suggesting that grazing tolerance may be related to the TNC concentration in roots of alfalfa that had been heavily and continuously grazed. This study indicates that selection for plant persistence under continuous grazing from a broad‐based population improved the grazing tolerance of the resulting germplasm (GA‐GC) while maintaining the potential for good forage yields.