Published in Agron. J. 95:1591-1594 (2003).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
PRODUCTION PAPERS
Persistence and Spread of Kura Clover in Cool-Season Grass Pastures
G. J. Cuomo*,a,
P. R. Petersonb,
A. Singhc,
D. G. Johnsona,
W. A. Head, Jr.a and
M. H. Reesea
a Univ. of Minnesota West Cent. Res. and Outreach Cent., State Hwy. 329, Morris, MN 56267
b Dep. of Agron. and Plant Genet., Univ. of Minnesota, St. Paul, MN 55108
c Organic Agric. Cent. of Can., Nova Scotia Agric. College, P.O. Box 550, Truro, NS, Canada B2N-5E3
* Corresponding author (cuomogj{at}mrs.umn.edu).
Received for publication December 10, 2002.
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ABSTRACT
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Legumes can improve productivity and quality of cool-season grass pastures but often do not persist under grazing. In May of 1997 and 1998, field experiments were planted in cool-season grass pastures near Morris, MN, to evaluate establishment and persistence of kura clover (Trifolium ambiguum Bieb.) compared with alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), and red clover (Trifolium pratense L.) under grazing pressure in the north-central USA. Each spring, from planting through 2002, stands of these legumes were evaluated for persistence. Pastures were grazed five or six times per growing season for 12-h grazing periods by lactating dairy cows (Bos taurus L.) over the duration of the study. Kura clover stand density was low relative to the other species in the growing season after establishment but increased and maintained denser stands in subsequent growing seasons. Alfalfa, birdsfoot trefoil, and red clover initially developed stands greater than 30% of the sward and remained constant or increased for two (1998 planting) or four (1997 planting) growing seasons before declining. In the spring of 2002, stands were greater (P > 0.001) for both planting years for kura clover (90%) compared with alfalfa, birdsfoot trefoil, and red clover (41, 28, and 9%) when averaged across planting years, respectively. Kura clover stands spread 60 (1998 planting) to 90% (1997 planting) over the length of the study. Stands of other species did not spread. In these studies, kura clover was able to compete, persist, and spread under intermittent grazing and has the potential to be an important and persistent component of cool-season grass pastures in the north-central USA.
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INTRODUCTION
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LEGUMES REDUCE RELIANCE on external N inputs and enhance animal performance in pastures, but lack of persistence is a major deterrent to more widespread adoption among producers (Beuselinck et al., 1994; Sheaffer et al., 1993; Smith and Kretschmer, Jr., 1989). Alfalfa, red clover, and birdsfoot trefoil are the legumes that are used most commonly for interseeding in the north-central region of the United States. However, alfalfa does not persist well in acidic or wet soils or under continuous grazing (Sheaffer et al., 1993). Red clover is susceptible to disease and drought (Sheaffer et al., 1993), and establishment and persistence of birdsfoot trefoil can be a challenge (Seaney, 1980).
Kura clover, a rhizomatous perennial, has shown promise for longevity in pastures of the north-central USA (Sheaffer et al., 1992). Exceptional winterhardiness, tolerance to drought (Black and Lucas, 2000; Watson et al., 1998), and tolerance to frequent defoliation (Peterson et al., 2002; Peterson et al., 1994a) have increased interest in the potential of kura clover as a component in pasture-based livestock production systems. These characteristics are linked to its extensive, root–rhizome complex (Peterson et al., 1994b). In Wisconsin, Holstein steers grazing kura clover/mixed cool-season grass pastures gained an average of 1.2 kg d-1 and more than 1000 kg ha-1 during 3 yr of rotational stocking (Mourino et al., 2002). The consistently superior gains of these steers compared with those grazing red clover–grass pastures was attributed to kura clover's superior productivity and nutritive value and the greater percentage of the total sward it exhibits relative to red clover.
Once established, kura clover spreads via rhizome growth (Genrich et al., 1998; Pryor et al., 1996). Vegetative propagation allows kura clover to expand its habitat to regions of low competition by colonizing open niches in the canopy. Albrecht and Kim (1998) demonstrated that reduced grass or weed competition can optimize the spread of rhizomes. However, Scott and Mason (1992) suggested that the slow spread of rhizobia resulted in nodulation failures, limiting the extent of spread of kura clover into unsown areas.
The spread of rhizomes, and in turn the persistence of kura clover in pasture mixtures, is influenced by its response to grazing (Hoveland, 1989; Sheath and Hodgson, 1989). Under intermittent stocking with sheep (Ovis aries L.), Sheaffer et al. (1992) showed that kura clover was an aggressive competitor against birdsfoot trefoil. Under more intense grazing, Peterson et al. (1994b) showed that frequent defoliation of a pure stand of kura clover had little effect on the amount of biomass below ground. In contrast, when grown in mixture with endophyte-infected hybrid ryegrass (Lolium sp.) in New Zealand, kura clover root and rhizome mass decreased under continuous stocking by sheep (Lucas et al., 1998). Kura clover stand dynamics have not been compared thoroughly against other perennial legumes in grazed, mixed grass–legume pastures in the north-central USA. This study was conducted to evaluate the persistence of kura clover compared with alfalfa, birdsfoot trefoil, and red clover in cool-season grass pastures with intermittent stocking in the north-central USA.
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MATERIALS AND METHODS
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The experimental site was located at the University of Minnesota's West Central Research and Outreach Center near Morris, MN. Average precipitation is 60 cm yr-1, with about 40 cm falling during the growing season. The experiment was conducted on a pasture with Doland silt loam (fine loamy, mixed, Udic Haploboroll) soils, which are undulating, well-drained soils formed in silty material underlain by glacial till. The A horizon extends to about 25 cm with glacial till beginning at about 60 cm. At the beginning of the study, soil pH was 7.7; in addition, organic matter, Olsen P (Olsen et al., 1954), and soil-test K were 4.0%, 32 mg kg-1, and 399 mg kg-1, respectively. No additional fertilization was applied during this experiment.
In 1997 and 1998, a split-split plot experiment with six replicates was planted in the first week of May. Whole-plot sod suppression treatments consisted of (i) applying 0.62 kg a.i. ha-1 glyphosate [isopropylamine of N-(phosphono-methyl) glycine] or (ii) applying no glyphosate. Subplot planting method treatments were applied 1 d after glyphosate application and consisted of (i) using a no-till drill, (ii) broadcasting seed on the soil surface, (iii) broadcasting seed followed by harrowing, and (iv) broadcasting seed followed by light disking. All broadcast treatments were applied by mixing the appropriate amount of seed for each treatment with about 0.45 kg of sand and hand-spreading on plots. Legume species sub-subplots were (i) ‘Amerigraze 401’ alfalfa, (ii) ‘Marathon’ red clover, (iii) ‘Endura’ kura clover, and (iv) ‘Norcen’ birdsfoot trefoil. Alfalfa was planted at 7.8 kg ha-1, and the other legume species were planted at 6.7 kg ha-1. Whole-plot sod suppression treatments were 6.8 by 16 m. Subplot planting method treatments were 6.8 by 4 m, and sub-subplot legume species treatments were 1.7 by 4 m.
For at least 30 yr before 1994, the experimental pasture had been grazed by beef cattle with little rotation from May through September. Beginning in 1995, and continuing through these trials, lactating dairy cattle grazed flexibly sized paddocks for 12 h at a stocking rate of about 56000 kg ha -1 lactating Holstein cow five or six times per grazing season (except during the establishment years). Grazing was initiated when forage height was 25 to 40 cm. When the trial was initiated in 1997, the pasture consisted of primarily smooth bromegrass (Bromus inermis Leyss.), quackgrass [Elytrigia repens (L.) Nevski.], and Kentucky bluegrass (Poa pratensis L.).
In the establishment phase of this study, stand establishment was consistently poor where sod suppression was not used, and no differences were detected for planting methods (Cuomo et al., 2001). Subsequently, stands in areas where sod was not suppressed with glyphosate did not develop satisfactorily and were excluded from the analysis in the current trial. Differences among planting methods were not detected. As such, data presented in this paper are averaged across planting method treatments where glyphosate was used to suppress existing vegetation during establishment.
After planting, the research area was fenced to exclude cows from grazing for 8 wk as per the glyphosate label. Thus, the experimental area was first grazed in early July and was grazed three times during the planting year. The 1997 and 1998 plantings were in relatively close proximity in the same pasture, and when grazing events occurred, the two experimental areas were grazed by the same groups of animals within 2 d of each other.
Stand data were collected each spring (late May or early June), 10 d after the first grazing event. Collecting data 10-d after the first grazing event allowed adequate time for legumes to express themselves during spring and to optimize visibility of legume regrowth. Stand data were collected using a 30- by 90-cm frame that had been divided into twenty-seven 10- by 10-cm quadrats. The number of quadrats that contained live rooted plants of the planted species were tallied and divided by 27 to attain a percentage value. The frame was randomly placed in two locations within each plot. Because kura clover spreads by rhizomes, individual plants could be hard to identify. In this study, if kura clover was rooted in the soil within a 10- by 10-cm quadrat, it was counted as a plant.
In this study, an acceptable stand was defined as at least 20% of the potential 10- by 10-cm quadrats containing a live rooted plant. If it is assumed that only one plant was present in each 10- by 10-cm quadrat, a 20% stand would be 20 plants m-2.
Spread of kura clover over the length of the study was evaluated by measuring the distance of the greatest width of rooted kura clover plants outside the boundary of each plot when stands were assessed in spring 2002. Other legume species did not spread beyond the initial planted boundaries of their plot.
The experimental design used in this analysis was a randomized complete block design and replicated over years. All statistical analyses were performed using GLM procedures of SAS (SAS Inst., 1996). Since stands were monitored for five growing seasons after the 1997 planting, and four growing seasons after the 1998 planting, data were analyzed by planting year. The error term used to test species whole-plot treatment effects was the block x species interaction. Residual error was used to test difference among growing seasons after planting and growing season after planting interactions. Spread of kura clover stands was evaluated only in 2002. As such, only planting year effects were tested. Residual error was used to test differences among planting years for spread of kura clover stands. Appropriate LSD values were calculated and used for mean comparisons. All differences reported are significant at P 
0.05.
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RESULTS AND DISCUSSION
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Climate Data
Average monthly high temperature and total precipitation data for May through August 1997 through 2001 and 100-yr averages for Morris, MN, are presented in Table 1. Summer maximum temperatures were near normal throughout the study (Table 1). Precipitation was well below average (<70% of average) in May and June of 1997 during the establishment period of the 1997 planting and in August of 2000 and 2001. All other months were at or near normal precipitation. Monthly average low temperature, days with less than 5 cm of average snow cover, and days when soil temperature at 5 cm was less than -9°C from November through March are presented in Table 2. Snow cover and soil temperature varied with years (Table 2). Days with soil temperatures below -9°C at 5 cm tended to be more frequent in the winters of 1997–1998 and 2001–2002.
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Table 1. Mean maximum temperature and precipitation data for May through August for 1997 through 2001, and 100-yr average for Morris, MN.
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Table 2. Number of days with less than 5 cm of snow cover, mean soil temperature at a depth of 5 cm, and number of days when soil temperature at 5 cm was below -9°C for November through March in the winters of 1997–1998 through 2001–2002 near Morris, MN.
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Stand Persistence
Interactions of growing seasons after planting and species occurred for stand density in both the 1997 and 1998 planting (Tables 3 and 4, respectively). Stands of legumes developed and declined differently over time. Initial kura clover stands were less dense than the other legumes, except for birdsfoot trefoil that was planted in 1997. Kura clover increased and achieved stable plant densities of greater than 80% in both planting years, whereas stands of other legumes began to decline by the end of the trials. This pattern of relatively slow establishment followed by robust stand development in kura clover has been reported in different management schemes and environments in Minnesota (Sheaffer and Marten, 1991), Michigan (Leep et al., 2002), and New Zealand (Black and Lucas, 2000). Red clover stands were relatively stable (Tables 3 and 4) in both plantings through the 2000 growing season (three growing seasons after the 1997 planting and two growing seasons after the 1998 planting) and then declined beginning with the 2001 growing season. Stands of alfalfa and birdsfoot trefoil developed more rapidly in the 1998 planting than the 1997 planting. This may, in part, be the result of the dry spring in 1997 and the cold soil temperatures and lack of snow cover between the 1997 and 1998 growing seasons (Tables 1 and 2). For both planting years, alfalfa and birdsfoot trefoil increased stand density in the years after planting. Increases in stands of alfalfa and birdsfoot trefoil may have been the result of hard seed, reseeding, or plant development that resulted in larger plant crowns that occupied more than one (10 by 10 cm) quadrat. Stands of alfalfa, birdsfoot trefoil, and red clover in both planting years were negatively impacted by the winter of 2001–2002. For red clover, some of this effect may be explained by stand age. Red clover is regarded as a short-lived perennial (Sheaffer et al., 1993). Additional explanations for stand decline of alfalfa, birdsfoot trefoil, and red clover between the 2001 and 2002 growing seasons include the lack of snow cover and relatively cold soil temperatures (Table 2). These findings are in agreement with Albrecht (2002), who reported that kura clover survived winters in Wisconsin when adjacent alfalfa and red clover fields were damaged. Additionally, after 15 yr of grazing in New Zealand, Allan and Keoghan (1994) reported good survival of kura clover but poor survival of several varieties of birdsfoot trefoil.
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Table 3. Kura clover, alfalfa, birdsfoot trefoil, and red clover stand density for five growing seasons after planting into existing cool-season grass pastures in 1997 near Morris, MN.
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Table 4. Kura clover, alfalfa, birdsfoot trefoil, and red clover stand density for four growing seasons after planting into existing cool-season grass pastures in 1998 near Morris, MN.
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Planting year effects were detected for the spread of kura clover (P > 0.015). By spring of 2002, plots of kura clover planted in 1997 had spread 1.5 m, to effectively make the width of kura clover plots 190% of the initial plot width. Kura clover plots planted in 1998 spread 1.0 m, or were 160% the width of the original plot. Other legumes did not spread outside of their planted borders. This was expected as alfalfa, red clover, and birdsfoot trefoil are not strongly rhizomatous. Since spread was only measured in 2002, it cannot be determined whether the additional growing season from the 1997 planting until 2002 accounts for the greater spread in the 1997 planting. However, Sheaffer and Marten (1991) reported that kura clover tended to be more vigorous as stands developed. These data indicate that kura clover has long-term competitiveness with cool-season grasses under intermittent stocking.
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SUMMARY
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This study demonstrated that slower establishment of kura clover relative to other legumes may not be a long-term problem when individual plants can become established at low densities and subsequently spread in cool-season grass pastures over time. Alfalfa, birdsfoot trefoil, and red clover all initially developed satisfactory stands but then declined over time in both planting years in this study. This was probably the result of some combination of physiological age of the plant, environment, and grazing pressure. Dense stands of kura clover developed, persisted, and spread during this study. Red clover, alfalfa, and birdsfoot trefoil currently tend to be the preferred species for interseeding in pastures in the north-central region. In these studies, kura clover was well adapted, more persistent, and not as sensitive to the environment as alfalfa, birdsfoot trefoil, and red clover. Kura clover competed with cool-season grasses under intermittent stocking and has the potential to be an important pasture legume in the north-central region of the USA.
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NOTES
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This research was supported by the Minnesota Agric. Exp. Stn.
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REFERENCES
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ABSTRACT
INTRODUCTION
