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Agronomy Journal 94:1257-1262 (2002)
© 2002 American Society of Agronomy

FORAGE MANAGEMENT

Grazing Effects on Herbage Mass and Composition in Grass–Birdsfoot Trefoil Mixtures

Richard Leepa, Peter Jeranyama*,b, Doo-Hong Minc, Timothy Dietza, Suleiman Bughraraa and James Isleibc

a Dep. of Crop and Soil Sci., Michigan State Univ., East Lansing, MI 48824
b Dep. of Plant Sci., Univ. of Saskatchewan, 51 Campus Dr., Saskatoon SK, S7N 5A8 Canada
c Michigan State Univ. Ext., Upper Peninsula Exp. Stn., Chatham, MI 49816

* Corresponding author (jeranyama{at}usask.ca)

Received for publication January 2, 2001.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Grass–legume mixtures have the ability to supply more consistent forage yields across a wide range of environments throughout the grazing season than do grass monocultures. The suitability of diverse grass species in binary mixtures with birdsfoot trefoil (Lotus corniculatus L.) in rotational stocking systems has not been extensively studied. The objective of this study was to evaluate binary mixtures of five cool-season grasses with the birdsfoot trefoil cultivar Norcen for herbage mass, botanical composition, and cattle (Bos taurus) grazing preference under a rotational stocking. Experiments were established at Lake City and Chatham, MI, in 1994. Binary mixtures were grazed for 2 yr with beef or dairy cows three times yearly at predetermined periods from spring to fall. Total herbage dry mass production ranged from 3 to 10 Mg ha-1 yr-1 over two years and locations. The grass fraction in binary mixtures was 327 to 946 g kg-1 in swards over two years and locations. Perennial ryegrass (Lolium perenne L.) failed to persist at Lake City, probably due to less consistent snow cover. Birdsfoot trefoil fraction was highest in binary mixtures with smooth bromegrass (Bromus inermis Leyss) and timothy (Phleum pratense L.). Binary mixtures with orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.) produced the highest herbage biomass but were less preferred by grazing animals while binary mixtures with timothy and smooth bromegrass were associated with the highest apparent herbage utilization at both locations (84–100%).


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
A DESIRE TO EXTEND the grazing season and reduce beef cow feed costs in the North-Central region, USA, has prompted an interest in grass and legume mixed pastures for grazing systems. Grass–legume mixture research has received very little attention in the North-Central region because alfalfa (Medicago sativa L.) has dominated forage research for the past four decades. Some notable benefits of legume–grass mixtures are their potential to supply more consistent forage yields across a wide range of environments compared with grass monocultures (Haynes, 1980) and N2 fixation by the legume in the mixture (Giller and Cadisch, 1995). Other potential advantages of grass–legume mixtures over monocultures include erosion control, minimized weed invasion inherent in monocultures (Sheaffer et al., 1990), improved drying time for hay (Chamblee and Collins, 1988), and reduced insect damage (Roda et al., 1995).

In Iowa, Mooso (1986) reported yield increases of 15 to 66% for binary seedings of grasses and legumes compared with single-crop seedings in 2 yr of trials. Kunelius and Narasimhalu (1983) reported that growing legumes in mixtures with perennial ryegrass increased yields 15 to 52% compared with Persian clover (Trifolium resupinatum L.), alfalfa, and birdsfoot trefoil grown in monoculture.

Grasses and legumes may compete for light, water, and soil minerals when grown in mixtures (Jones et al., 1988). Competition for light is often considered to be the most critical of these in humid environments (Donald, 1961). In general, legumes often have deeper root systems than grasses (Chamblee, 1972), and legumes also exhibit lower water use efficiency (Haynes, 1980; Snaydon, 1978). The fibrous nature and high cation-exchange capacity of grass roots give them an advantage over legumes in extracting monovalent cations from the soil (Haynes, 1980).

Coexistence results when the mixture components are limited by different growth factors or exhibit balanced competitive abilities for the same growth factors (Aarssen, 1983). The N relationship in grass–legume mixtures seems to be uncompetitive unlike the highly competitive relationship for light, water, and other nutrients (Haynes, 1980; Vallis et al., 1967). Some researchers have reported total dry matter reduction (Waddington and Bittmen, 1984) and reduced forage quality (Spandl and Hesterman, 1997) in grass–legume mixtures. In general, crude protein is reduced and fiber content increased in the first cutting in legume–grass mixtures compared with legume monocultures due to rapid morphological development of grasses compared with legumes. By the time of first cutting, the grass may already be flowering, and its quality declines faster than that of legumes (Smith, 1981).

Several legumes have potential for use in grazing systems but all have limitations. Alfalfa, which is primarily used as a hay crop, causes bloat and requires insect control, deep soils, and high soil fertility. Kura clover (T. ambiguum Bieb.), a perennial legume with potential for use in grazing, is slow to establish, can cause bloat, and may not be sufficiently competitive in legume–grass mixtures in the establishment year (Sheaffer et al., 1992). Birdsfoot trefoil can support good short-term carrying capacity and animal weight gain but lacks persistence. Additionally, birdsfoot trefoil is nonbloating and a good grazing alternative to alfalfa in the North-Central USA (Marten et al., 1987).

Many factors influence the stability of grass–legume mixtures. Short and Carlson (1989) reported that tiller number in orchardgrass was the single most important trait influencing birdsfoot trefoil yield in the binary mixture. Orchardgrass genotypes with lower tiller numbers were closely associated with higher birdsfoot trefoil yields. Tall fescue is considered to be an aggressive, competitive forage grass in mixtures with birdsfoot trefoil (Beuselinck et al., 1992).

Tall fescue is commonly grown with red clover (T. pratense L.), which is shade tolerant and more aggressive than birdsfoot trefoil, alfalfa, or other legumes (McKee, 1962). Previous research has recommended timothy and Kentucky bluegrass (Poa pratensis L.) for binary mixtures with birdsfoot trefoil (Chevrette et al., 1960; Schlough et al., 1977). Although the suitability of diverse grass species in binary mixtures with birdsfoot trefoil has been studied, few studies under rotational stocking have been reported. The objective of this study was to evaluate binary mixtures of cool-season grasses with the birdsfoot trefoil cultivar Norcen for herbage mass, botanical composition, and grazing preference under rotational stocking.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Experiments were seeded on 27 and 29 May 1994 with five cool-season grass species (Table 1) and the birdsfoot trefoil cultivar Norcen at the Lake City Experiment Station, MI (44°19' N, 85°12' W), on a Nester soil (fine sandy loam, mixed Typic Eutroboralfs) and at the Chatham Experiment Station (Upper Peninsula), MI (46°33' N, 86°55' W), on a Ternary soil (sandy loam, mixed, frigid Alfic Haplorthodes). Chatham Experiment Station has lake-enhanced normal seasonal precipitation of 88 cm, and daily minimum winter temperatures fall to -18°C or lower an average of 26 times in a season. There is a mean of 91 d frost free and mean annual maximum and minimum temperatures of 11 and -3°C (Eichenlaub et al., 1990). Lake City has average annual precipitation of 73 cm, growing season length of 108 d frost free, and mean annual maximum and minimum temperatures of 12 and 0°C, respectively (http://climate.geo.msu.edu/e-upper.html; verified 27 June 2002).


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  		Table 1. Common, scientific, and cultivar names of species used in experiment.

 
Cultivars within species ranged from one to eight (Table 1), but data are reported as the means of cultivars for each species. Both K and P were added according to Michigan State University Soil Testing Laboratory recommendations. No supplemental N was added during the experimental period. Each plot was seeded with a different grass cultivar and Norcen birdsfoot trefoil as a binary mixture in small plots of 1.8 by 7.6 m arranged in a randomized complete block design replicated four times at each site, so each replication had 26 plots. Seeding rates for grasses were as follows: smooth bromegrass at 9.0 kg ha-1, orchardgrass at 2.2, timothy at 1.1, and perennial ryegrass and tall fescue at 5.6. Birdsfoot trefoil seed was inoculated with Rhizobium loti before planting at 11.2 kg ha-1. A plot planter with a cone seeder (Carter Manufacturing, Brookston, IN) was used to seed small plots in rows 0.15 m apart. Borders of the grazing areas were seeded to a birdsfoot trefoil and smooth bromegrass mixture.

One year after seeding, a conditioned Simmental beef herd at Lake City and Holstein dairy cows at Chatham were used to graze until an average plant height of 5 to 8 cm was left on the most preferred grass species. We used mob stocking technique, which is less sensitive to differences in palatability among germplasm than continuous stocking. Paddocks are stocked heavily to ensure that all germplasms are grazed uniformly within a few days (Bittman and McCartney, 1994). The mob stocking technique has been used to evaluate a large number of pasture grasses (Mislevy et al., 1982). In this study, cattle were conditioned by pregrazing binary mixtures of the same treatments planted outside the experimental area. On average, a grazing event lasted 2 d, depending on the amount of forage available. The plots were grazed on 30 May, 15 July, and 3 Oct. 1995 and on 1 June, 17 July, and 12 Oct. 1996. The initial grazing each year was conducted before emergence of the inflorescence on grasses. The stocking rate in this experiment ranged from 6 to 16 animals ha-1 d-1. Herbage mass was estimated by hand clipping from a 0.25-m2 quadrat randomly placed in each plot to a height of 5 cm before (pregrazing herbage mass) and 48 h after (postgrazing herbage mass) a grazing event. Samples taken before grazing were also used to evaluate the botanical composition of swards and were hand-separated into grass, birdsfoot trefoil, and weeds; dried at 60°C for 72 h; and weighed. Apparent utilization of herbage mass was measured as the different between pre- and postgrazing herbage mass; however, apparent herbage utilization was not measured in 1996.

Statistical Analysis
The experimental design was a randomized complete block with treatments replicated four times. Data were analyzed as a repeated-measures experiment with a first-order autoregression correlation type [AR(1)] over grazing events and years in PROC MIXED of SAS (SAS Inst., 1997).

Due to a significant F (P <= 0.05) four-way interaction of year x location x species x grazing event, a reduced model was used within a year and location. In the reduced model, data were analyzed as a randomized complete block design in PROC GLM of SAS (SAS Inst., 1997). Means separation on data were conducted using LSD according to Snedecor and Cochran (1980).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Herbage Mass
There were no significant (P <= 0.05) differences in herbage mass and relative pasture use among cultivars of the same grass species. Significant year x location, year x species, and location x species interactions occurred for herbage mass, pre- and postgrazing herbage mass, and apparent herbage utilization.

Total seasonal herbage mass production in the two grazing years ranged from 5.4 to 10.0 Mg ha-1 yr-1 in Lake City and from 2.9 to 7.3 Mg ha-1 in Chatham (Table 2). These herbage masses are similar to irrigated herbage mass of legume–grass mixtures (Guldan et al., 2000) and three-harvest herbage masses of nonirrigated legume–grass mixture (Sleugh et al., 2000), but they are higher than those reported by Riesterer et al. (2000) for cool-season grasses following winter defoliation.


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  		Table 2. Herbage mass in binary mixtures of birdsfoot trefoil and cool-season grasses before first, second, and third grazing events in 1995 and 1996 at Lake City and Chatham, MI.

 
In Lake City, herbage mass of binary mixtures of birdsfoot trefoil with smooth bromegrass, orchardgrass, and tall fescue was significantly (P <= 0.05) higher than that of mixtures with timothy and perennial ryegrass before the first grazing event in 1995 (Table 2). In contrast to the first grazing event, herbage mass of binary mixtures of birdsfoot trefoil with perennial ryegrass was significantly higher than that of the other species except orchardgrass before the second grazing event. Just before Grazing Event 3, herbage mass of binary mixture of birdsfoot trefoil with perennial ryegrass was significantly lower than that of the other grass species. However, there were no significant differences in total seasonal herbage mass among binary mixtures at Lake City in 1995 (Table 2). In 1995, herbage mass of binary mixtures of birdsfoot trefoil was not significantly different among grass species in Chatham. Herbage masses were lower at Chatham than at Lake City (Table 2) and decreased from 1995 to 1996. The lower total seasonal herbage mass at Chatham was likely due to a shorter growing season. (Lake City has a 16 d longer frost-free period than Chatham.) In 1996, at Grazing Event 3, herbage mass of tall fescue with birdsfoot trefoil at Lake City was significantly higher than other grass species, resulting in significantly higher total seasonal herbage mass than other binary mixtures.

At Chatham in 1996, herbage mass of smooth bromegrass and orchardgrass showed more even yield distribution compared with timothy, perennial ryegrass, and tall fescue. After the second grazing event, herbage yields of timothy, perennial ryegrass, and tall fescue were reduced dramatically compared with smooth bromegrass and orchardgrass. At both locations, when examined over the 2 yr, no binary mixture combination of birdsfoot trefoil and grass showed a consistent distribution of herbage mass during the season. Perennial ryegrass winter-killed at Lake City in 1996, and no data were reported for that binary mixture in that year. Perennial ryegrass is usually less winter hardy than orchardgrass and is less drought tolerant than smooth bromegrass (Balasko et al., 1995).

Sward Composition
Lake City
Herbage mass constituted 327 to 852 and 549 to 939 g kg-1 grass in swards in 1995 and 1996, respectively (Table 3). In 1995, orchardgrass, perennial ryegrass, and tall fescue mixtures produced similar fractions of herbage mass and were the highest of the five grasses (Table 3). In Grazing Event 1 in 1995, the ratio of grass to birdsfoot trefoil was higher in orchardgrass, perennial ryegrass, and tall fescue than in smooth bromegrass and timothy. This indicates that smooth bromegrass and timothy were less competitive with birdsfoot trefoil than the other grasses at Lake City.


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  		Table 3. Dry matter (DM) composition of birdsfoot trefoil (BFT), grasses, and weeds in three grazing events in 1995–1996 at Lake City, MI.

 
At Lake City in 1996, the only difference in grass fraction was in the third grazing event where timothy was significantly lower than orchardgrass and tall fescue. Weed fraction values were least in tall fescue mixtures in 1996, but only in the smooth bromegrass mixtures at the first grazing event in 1996 did the weed fraction exceed 10% (Table 3).

At Lake City, the fraction of birdsfoot trefoil in mixtures ranged between 131 and 410 g kg-1 by the third grazing in 1995 and by the third grazing in 1996, ranged between 63 and 234 g kg-1 dry matter for the four remaining mixtures. The decrease in birdsfoot trefoil fraction in swards by the third grazing event could be due to reduced vigor of birdsfoot trefoil after two grazing events and increased competitive edge of the grass coming from a decline dry matter production into high production in fall as conditions become favorable. Similar results were obtained by Sleugh et al. (2000).

Chatham
Grass herbage mass constituted 332 to 743 and 406 to 946 g kg-1 grass in swards in 1995 and 1996, respectively. In both years, as at Lake City, orchardgrass and tall fescue contributed the highest fraction of grass to herbage biomass in swards compared with other species such as timothy (Table 4). Similar results were obtained by Smith et al. (1973). This is because orchardgrass and tall fescue were more competitive with legumes in binary mixtures than other cool-season grasses. Weed suppression was greater in 1996 than in 1995, and binary mixtures with timothy consistently had the lowest weed fraction in 1996 (Table 4).


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  		Table 4. Dry matter (DM) composition of birdsfoot trefoil (BFT), grasses, and weeds in three grazing events in 1995–1996 at Chatham, MI.

 
Unlike mixtures at Lake City, the birdsfoot trefoil fraction of mixtures had increased by the third grazing in 1996, ranging between 301 and 524 g kg-1 dry matter. Chatham has a cooler growing season as well as a more consistent snow cover during the winter months (Natl. Oceanic and Atmos. Administration, 1993–1997) compared with Lake City. Leep et al. (2001) reported that snow cover at Chatham significantly moderated air temperatures at the plant level and was associated with greater subsequent perennial forage yields and that snow cover of >=10 cm adequately provided protection from winter injury. Therefore, the persistence of both perennial ryegrass and birdsfoot trefoil at Chatham as opposed to Lake City could have been due to the differences in snow cover.

Animal Preference
Animals preferred timothy and smooth bromegrass mixtures throughout the grazing season at Lake City as indicated by low postgrazing herbage mass (Table 5). This was also the case for the first grazing event at Chatham. This preference may have been due to the higher fraction of birdsfoot trefoil in these mixtures at Lake City. However, at each grazing period, timothy was the least mature and in the vegetative growth stage (Table 5). Although tall fescue was less advanced in growth compared with perennial ryegrass, it was apparently the least palatable as indicated by postgrazing herbage mass at Lake City. It was not due to endophyte infection (Acremonium coenophialum) as the cultivars planted were endophyte free. In Chatham, cattle preferred mixtures with the greatest available forage mass (Table 5). Postgrazing data for 1996 were not recorded.


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  		Table 5. Pregrazing herbage mass and apparent herbage utilization in birdsfoot trefoil–grass mixtures in 1995 at Lake City and Chatham, MI.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Herbage mass ranged from 2.9 to 10.0 Mg ha-1 yr-1 across locations. Grass constituted 327 to 946 g kg-1 sward dry matter, with orchardgrass and tall fescue producing the highest fractions of herbage mass on average. Birdsfoot trefoil fraction decreased by the third grazing in both years at Lake City. However, at Chatham, birdsfoot trefoil fraction increased by the third grazing event. Differences in performance of birdsfoot trefoil were due to differences in growing conditions at each location. Animals preferred timothy and smooth bromegrass mixtures to others. Tall fescue mixtures were the least palatable. Perennial ryegrass should be considered only as a short-term solution for pasture renovations in the North-Central USA where severe winterkill is common. Because timothy and smooth bromegrass were both compatible with birdsfoot trefoil and were persistent in this study, these cool-season grasses would be excellent choices for rotational stocking with birdsfoot trefoil.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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