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Published online 8 September 2006
Published in Crop Sci 46:2062-2068 (2006)
© 2006 Crop Science Society of America
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FORAGE & GRAZINGLANDS

Pasture and Cattle Responses in Rotationally Stocked Grazing Systems Sown with Differing Levels of Species Richness

Benjamin F. Tracya,* and Dan B. Faulknerb

a Dep. of Crop Sciences, Univ. of Illinois, Urbana, IL 61801
b Dep. of Animal Sciences, Univ. of Illinois, Urbana, IL 61801

* Corresponding author (bftracy{at}uiuc.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Increasing species richness of temperate pastures beyond one or two forage species could improve grazing system productivity. An experiment in western Illinois, USA, was initiated in August 2001 to test this idea. The main study objective was to determine how pastures sown with increasing levels of species richness would affect herbage yield and cow-calf performance. Three seed mixtures that contained three, five, or eight forage species were sown into 3- to 6-ha pastures. Mixtures were replicated three times and rotationally stocked with beef cow–calf groups. Herbage mass and accumulation were estimated by a rising plate meter method and weight gain evaluated cow–calf performance. We also evaluated forage nutritive value indices and changes in forage species composition. After pasture establishment in 2001, herbage mass was marginally higher (P = 0.15) in eight-species mixtures (98 g m–2) compared with three-species mixes (43 g m–2). Once grazing started, pasture mix had no effect on herbage responses or stocking rate (P > 0.05). Cow–calf performance was also unaffected by pasture mix, although average daily gain (ADG) was higher in 2003 (P < 0.05). Cow and calf ADG averaged 0.33 and 1.17 kg d–1, respectively, in 2003 compared with 0.05 and 1.01 kg d–1 in other years. Overall, species richness in pastures had minimal effects on forage yield and cattle performance. Grazing management (e.g., stocking rate) and climatic conditions more strongly influence grazing system productivity.

Abbreviations: ADG, average daily gain • E–, endophyte-free • E+, endophyte-infected • NDF, neutral detergent fiber


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
THE SPECIES richness of plants in a pasture refers to the number of species existing within that defined area (Magurran, 1988). Temperate pastures typically have high plant species richness, but this richness is dominated mostly by weedy species with few desirable forage species—usually one or two (Tracy and Sanderson, 2000). Desirable forage species in this case refer to species that are purposely sown or maintained in a pasture because they have production value for livestock. Increasing the species richness of forage species in pasture beyond one or two species may have beneficial effects on forage yield. Several studies provided evidence that species-rich grasslands tend to have higher forage yields compared with less species-rich grasslands (Ruz-Jerez et al., 1991; Daly et al., 1996; Bullock et al., 2001). For example, Bullock et al. (2001) showed that forage yields were higher in haylands sown with a diverse mixture plants (>25) compared with simpler mixtures. Other research has shown small increases in forage yields when mixture complexity was increased from one to two species to nine to 15 species (Deak et al., 2004). More ecologically oriented studies have also shown that increased species richness in grasslands may improve yields (Tilman et al., 1996, 2001; Hector et al., 1999). The actual mechanisms behind these positive relationships between species richness and yield have been questioned as to whether they represent true diversity effects. Some suggest that the positive relationship between richness and yield mainly reflects a strong influence of one or two species in a species-rich community while the other species contribute minimally (Huston, 1997; Wardle, 1999).

Little is known about how increased forage species richness might affect cattle performance (Sanderson et al., 2004). Cattle grazing species-rich pastures may exhibit better performance because they have the opportunity to select from a variety of forage plants. Some benefits cattle gain from foraging on diverse diets can include reduced toxin consumption, optimization of foraging and rumination time, maintenance of a diverse rumen microflora, access to sample foods, and an overall more balanced diet (Provenza, 1996). Diet selection by ruminants is typically thought to be driven by a desire to meet nutritional needs and reduce over ingestion of toxic secondary compounds found in most plants (Freeland and Janzen, 1974; Westoby, 1978). As a result, if ruminants have a choice they will often select diets from an array of plant species that vary in levels of required nutrients or toxin. Interestingly, even when ruminants have access to single forages that meet nutritional needs and are not high in toxic compounds, they will still seek out a variety of plants to eat (Parsons et al., 1991; Provenza, 1996; Provenza et al., 1996).

The main objective of this study was to determine how pastures sown with increasing forage species richness affect forage yield and beef cattle performance. Our working hypothesis was that pastures sown with greater species richness are more productive and show better cattle performance than simpler pastures. A secondary objective was to measure how sown species composition of different pasture mixtures changed over time because potential changes in species composition could feed back to affect forage yields and cattle performance.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The experiment was conducted from August 2001 to October 2004 at the University of Illinois Orr Center Beef Unit located at Baylis, IL (39.7° N, 90.9° W, altitude 206 m). The Center has 24 pastures ranging between 3 and 6 ha located on rolling deep-loess soils (primarily Hapludalfs, Ochraqualfs, and Albaqualfs). The pastures have been used to supply forage for beef cattle herds housed at the research station since 1990. Pasture management previous to our experiment could best be described as low input. In August 2001, nine of the pastures were renovated by first treating existing vegetation with one application of glyphosate isopropylamine salt herbicide (1.12 kg a.i. ha–1). Existing sods then were turned with a moldboard plow, disked, and finally harrowed to prepare a clean seedbed. Previous to renovation, pastures contained mostly tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire], Kentucky bluegrass (Poa pratensis L.), and red clover (Trifolium pratense L.). Aside from occasional red clover frost seeding, the nine pastures had not been planted with any new species since at least 1979. Before start of the experiment, 15 to 20 soil samples were taken in each pasture (15-cm depth, 2.54-cm diameter) and subjected to standard soil analyses for pH, P, K, and organic matter (Alvey Labs, Belleville, IL). Before planting, all pastures received 44 kg N ha–1 as urea and individual pastures were fertilized with DAP (diammonium phosphate) or potash as recommended by soil test (Table 1). Pastures received no external fertilizer in subsequent years of the study. We felt that the legumes sown into the pastures would be sufficient to maintain favorable N status during the course of the study. Daily rainfall and air temperature data were recorded from a weather station located on the Orr Center property (Table 2).


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  		Table 1. Soil fertility variables before start of experiment in 2001. Complex, medium and simple refer to 8, 5, and 3 sown species, respectively. One medium pasture was removed from the study due to weed invasion.

 

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  		Table 2. Growing season air temperature and precipitation recorded at the Orr Research Center, Baylis, IL. Monthly temperature values are means calculated from daily average temperature.

 
Treatments were arranged in a completely randomized design with three replications. Treatments consisted of three pasture mixtures containing three, five, or eight forage species (Table 3). Hereafter, these mixtures will be referred to as simple, medium, and complex, respectively. Each mixture was sown at a rate of 22 kg ha–1 into three pastures. All mixtures contained tall fescue, orchardgrass (Dactylis glomerata L.), and white clover (Trifolium repens L.). An endophyte-free variety of fescue (E–) was used in all mixtures (Tracy and Renne, 2005). Additional forage species in mixtures were chosen on the basis of personal experience and previous experiments that suggested they would do well in mixture. For example, previous work showed that seeding more than 10 species had little additional benefit in forage yields compared with simpler mixtures (Tracy and Sanderson, 2004). Highly complex mixtures (>10 species), then, were excluded from the experiment. One replication of the intermediate mix was removed from the experiment during the first year of establishment because of heavy weed invasion.


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  		Table 3. Forage species and seeding rates (dry seed wt. basis) for pasture mixtures. Areas for each of the nine pastures originally sown in experiment are also given.

 
Grazing Methods
In May 2002, each pasture was divided into six equal-sized paddocks. Each year cow–calf pairs (black purebred Simmental cattle) were randomly assigned to pastures to achieve an initial stocking rate of 2.5 cows ha–1. Calves were all winter born (January or February) and weaned at an average age of 210 to 235 d. Cows were between 3 and 4 yr old. Five or six cow–calf pairs (heifer calves) remained on pasture at all times to serve as tester animals. After the first rotation through all paddocks, bull calves were weaned and their dams were used as put-and-take animals to maintain a residual forage canopy of height of 7 to 12 cm. The put-and-take cows were of similar size, weight, and breed and managed on adjacent pastures at the Orr Beef Center. In 2002, paddocks were grazed for 6 d with 30 d of rest. In subsequent years, paddocks were grazed for 3 d in the spring instead of 6 d because of the rapid forage regrowth. As the season progressed, the grazing period was lengthened to 6 d as forage regrowth slowed. Pastures were grazed with cow–calf pairs during the following dates: 17 May 2002 to 9 Sept. 2002, 23 Apr. 2003 to 8 Sept. 2003, and 27 Apr. 2004 to 8 Sept. 2004. After weaning, pastures were rotationally stocked with cows until late November when forage availability became limiting. Cows were removed from pasture and housed at the Orr Center facilities during the winter. Data on forage yields and cow performance in late fall are not presented because we were most interested in cow–calf performance during summer months.

Herbage Mass and Accumulation
Herbage mass and accumulation were measured in each pasture to evaluate performance of different mixtures (Forage and Grazing Terminology Committee, 1992). Herbage mass was considered the pregraze forage biomass measured in each paddock. Herbage mass was averaged for each paddock by summing pregraze values across sampling dates and dividing by the number of sampling dates per year. For statistical analyses, herbage mass in the six paddocks was averaged and expressed on a pasture basis. Herbage accumulation was calculated as the difference between pregraze herbage mass of a current grazing cycle and postgraze herbage mass of the previous cycle. Herbage accumulation for the first grazing cycle was treated as pregraze herbage mass. Total herbage accumulation was the sum across grazing cycles within a year. Forage regrowth during actual grazing events could not be accurately estimated so were not included in the calculation. Reported forage accumulation rates, then, may be slightly underestimated.

Before grazing began, herbage mass was estimated from clipped plots in November 2001 and May 2002. Herbage mass within 10 randomly located quadrats (10 x 100 cm) was clipped to ground level, dried for 48 h at 60°C and weighed. Once grazing started in 2002, forage mass was measured by a rising-plate meter technique (Mitchell and Lange, 1983). Before and after grazing bouts, 20 plate meter readings were taken in random locations around each paddock. This number of plate meter readings was used in a previous study at this location and was found to work adequately (Bertelsen et al., 1993). Canopy height measurements were calibrated to herbage mass by clipping and weighing the vegetation below 25 plate meter readings in each of the respective mixtures. Both pre- and post-graze conditions were calibrated. Calibrations were done in June each year of the study and rechecked each fall. The r2 values for the calibrations varied between 0.81 to 0.94 for respective mixtures.

We report only herbage mass and accumulation measurements taken from late spring to early September, which was when calves were weaned. We felt that potential yield differences due to the forage mixture richness would be most apparent after the spring flush when climatic conditions became more stressful for cool-season forages. In the upper midwestern and northeastern USA, cool-season forage species usually exhibit a bimodal productivity distribution with maximum levels occurring in the spring and fall and minimums in the summer when the weather becomes hot and dry (Moser and Hoveland, 1996). Inclusion of drought-tolerant species in complex mixtures may help improve forage yields during mid-summer. If this is the case, we might expect to see the largest potential differences among mixtures over this time period. Moreover, it was difficult to accurately measure herbage mass in the early spring because grasses rapidly grew tall and often exceeded the plate meter height. Specifically, data on herbage mass and accumulation were measured from dates 20 June 2002 to 9 Sept. 2002, 11 May 2003 to 8 Sept. 2003, and 18 May 2004 to 8 Sept. 2004. During these periods, each paddock was grazed three or four times. The later starting date in 2002 occurred because cattle were unavailable earlier. Stocking rate (cows ha–1) was also used as an indirect way to evaluate pasture performance. We expressed stocking rate as cows ha–1 because this value reflects put-and-take cows added to the tester pairs on pasture. Stocking rate was not calculated in 2004 because of missing data in mid-summer, but cow numbers were similar to 2003.

Forage Nutritive Value
Forage nutritive value among pasture mixtures was compared from samples taken each September. We were most interested in potential forage nutritive value differences among mixtures and felt that measuring nutritive value once a year would give us an indication of potential differences. Ideally, forage nutritive value should have been measured each month to better predict potential variation in cattle performance. In the same paddocks where species composition was measured, six to eight quadrats (10 x 50 cm) were clipped from random locations. The subsamples in each paddock were bulked together, dried for 48 h at 60°C, and analyzed for crude protein, acid detergent fiber, and neutral detergent fiber by near-infrared reflectance spectroscopy (Alvey Labs, Belleville, IL).

Plant Species Composition
Plant species composition of pastures was estimated each September except 2001, when pastures were sampled in November. In three paddocks of each pasture, percentage ground cover of all plant species and bare ground was visually estimated in eight randomly located quadrats (0.5 x 2 m). The same paddocks were sampled at each interval. Visual estimates were done by the senior author at each sampling date. Percentage cover of species in the three paddocks was averaged because paddocks were at different stages of defoliation and regrowth. For the 2001 sampling, 10 randomly located quadrats were sampled in each pasture because the paddocks had not been constructed. Species frequency was calculated as percentage of quadrats in which a respective species was encountered. Species frequency is less sensitive than percentage cover to climatic variation and current grazing bouts so we used this index to indicate species change (Hartnett et al., 1996). We were most interested in how the abundance of sown perennial species changed over the course of this experiment so felt that measuring species frequency once each year would be sufficient to address our objectives.

Cow–Calf Performance
Different cows were assigned to pastures each year of the trial, so we cannot evaluate the cumulative effects of different pasture mixtures on cow–calf performance. Yearly cow and calf performance on different mixtures was measured by comparing responses of ADG and gain per hectare. Performance data on put-and-take animals and cows grazing in fall were not recorded. Cow and calf weights were taken before animals were released on pasture in spring and in early September when the heifer calves were weaned. In each case (before and after grazing season), body weights were measured on two consecutive days with a 48-h feed and water shrink. The mean body weight over the 2 d was used to calculate ADG and gain per hectare variables.

Pasture and cattle responses were analyzed by ANOVA in the GLM procedure of SAS (SAS, 2003). In all cases, pasture was considered the experimental unit with treatments (mixtures) replicated three times. An exception was the intermediate mixture, which had two pastures, n = 2. Subsamples for herbage and cattle variables were averaged within each pasture treatment. For all measurements except initial herbage mass in 2001, pasture mixture and year were used as independent effects. If significant mixture x year interactions were found (P < 0.05), years were analyzed separately to determine differences among mixtures. Tukey's HSD (Honestly Significant Differences) test was used to evaluate treatment differences of significant main effects (P = 0.05). Changes in plant species composition were qualitatively evaluated by comparing means (± 1 SE) among years.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Herbage Mass and Accumulation
Pastures established quickly in 2001 because of adequate rainfall and mild temperatures that fall. Initial herbage mass measured in November 2001 showed a trend toward higher mass in the complex mixtures (P = 0.15). Complex, medium, and simple mixtures averaged 98 ± 4.1, 76 ± 23, and 43 ± 5.5 g m–2, respectively (means ± 1 SE). The added species richness in the complex mixtures, particularly rapid establishment of perennial ryegrass (Lolium perenne L.) and chicory (Cichorium intybus L.) contributed to this effect. In fact, complex mixtures had enough herbage in November that these pastures could have supported grazing before winter. Once grazing started in 2002, we found that pasture mix had no effect on herbage mass, accumulation or stocking rate (Table 4). Mixture x year interactions were also not significant (P > 0.05). The lack of herbage differences among pasture mixtures supports some of our previous work. Tracy and Sanderson (2004) found no yield differences in grass–legume mixtures that were sown with three to 15 species. Results from the present study suggest that planting two or three forage species that are well matched for local environmental conditions is a cost effective way to maintain consistent forage productivity. Sowing complex mixtures (>three species) of species may cost more to establish and may not improve yields substantively. At this site, a mixture of tall fescue, orchardgrass, and white clover seem to be particularly well suited to local conditions.


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  		Table 4. Mean pregraze herbage mass, herbage accumulation, and stocking rate in the three mixtures. Values are means ± 1 SE. Letters that differ are significantly different (P < 0.05) using Tukey's HSD.

 
Herbage responses differed by year with significantly higher values in 2003 relative to other years (Table 4). Herbage accumulation was highest in 2003 likely because of favorable weather conditions. Rainfall that July was approximately 30% greater than the 30-yr average and temperatures were not excessively high (Table 2). These factors probably contributed to the especially high forage accumulation rates measured during the grazing cycle that month. The comparatively lower yields in 2004 may have resulted from N stress. The pastures received no external fertilizer after initial establishment and had lower legume abundance than previous years (see Table 5). The lack of N inputs from fertilizer and legume biomass may have limited grass growth in 2004 more than other years. The lower yields in 2002 may reflect later grazing inception that year. Grazing began in mid-May in 2002 and by this time many of the grasses had already produced culms. The excessive plant biomass and trampling by cattle created a thick mat of litter over much of the pasture area. Since grass regrowth after reproduction depended on new tillers arising from basal axillary buds, excess litter that remained from the spring reproduction may have shaded buds and reduced tiller production.


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  		Table 5. Relative frequency and ground cover of sown species in the three mixtures. Cover values do not include bare ground and species that were not sown in pastures. Data are means ± 1 SE.

 
Although we found no effects of mixture on pasture performance, adding forage species to pastures may help sustain yield during drought (Tilman and Downing, 1994; Sanderson et al., 2005). This occurs as drought-tolerant species in complex mixtures compensate for yield losses of drought-sensitive species during dry seasons. There were no extended drought periods during the 4 yr of the current study; thus, there was no opportunity for complex mixtures to demonstrate an advantage in drought tolerance. Given the extra seed costs and difficulty with managing highly complex mixtures, however, a better strategy to cope with drought might be to integrate pastures planted with warm-season grasses (C4 photosynthesis pathway) in the grazing system (Moore et al., 2004). In this way, cattle can be moved from cool-season pasture to more drought-tolerant, warm-season pastures during droughts or the hottest parts of the summer when cool-season pastures are unproductive.

Forage Nutritive Value
Forage nutritive value indices showed significant treatment x year interactions (P < 0.001) because of differences in the simple mixtures from 2002 to 2003. In 2003, crude protein was lower in simple mixes compared with complex and medium mixtures (Table 6). Simple mixtures had less white clover in 2003 compared with other mixtures (Table 5), and this may explain the lower CP values measure that year. In 2002, simple mixtures had statistically higher CP values than other mixtures, but we have no explanation for that pattern. No other consistent differences among forage nutritive value indices were noted among the mixtures.


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  		Table 6. Herbage crude protein, acid detergent fiber (ADF), and neutral detergent fiber (NDF) measured in September of respective years. Values are means ± 1 SE. Letters that differ are significantly different (P < 0.05) using Tukey's HSD.

 
Plant Species Composition
Sown species accounted for approximately 80% of the ground cover in pastures with the remainder consisting of nonsown, weedy species, and bare ground. Most sown broadleaf species declined in abundance over this study. Chicory and red clover showed the sharpest declines and largely disappeared by 2004 (Table 5). Both species are considered short-lived perennials and typically decline in abundance over 2 to 3 yr (Taylor and Smith, 1995; Belesky et al., 1999; Labreveux et al., 2004). Although red clover can be effectively frost seeded into pastures (Casler et al., 1999), the usefulness of chicory in pasture mixes remains questionable because it may not be economical to re-establish this species through frost seeding (Sanderson et al., 2005). Alfalfa (Medicago sativa L.) and smooth bromegrass (Bromus inermis Leysser) also declined in frequency and white clover only appeared to decline from 2003 to 2004. Smooth bromegrass persistence can decrease if grazing occurs at prejoint or early head stages of development in the spring (Casler and Carlson, 1995). Grazing bouts occurred during these times in our study, and this may have reduced smooth bromegrass abundance. Careful grazing management is required to maintain high levels of smooth bromegrass over time. Among other grasses, tall fescue and orchardgrass showed a tendency toward increased abundance over the 4 yr, suggesting these species are well adapted to this location or that our management favored survival of these species in mixture. Although perennial ryegrass is generally considered less stress tolerant than fescue and orchardgrass (Jung et al., 1996), it remained at a relatively stable abundance during the study (Table 5). Perennial ryegrass persistence may be reflective of the mild growing seasons and the fact that we experienced no prolonged drought conditions during the study (Table 2).

Cattle Performance
Although grazing can have a major effect on plant species diversity (Hartnett et al., 1996; Howe, 1999), little data exist about how plant species richness may affect cattle performance. As with forage responses, pasture species richness had little effect on performance of both cows and calves (Table 7). No significant mixture x year interactions were found for cattle responses (P > 0.05). These results agree with other studies investigating the importance of species mixture in affecting cattle performance. Soder et al. (2004) found no differences in milk production in dairy cattle grazing cool-season mixtures that ranged from two to nine species. On irrigated alfalfa and tall wheatgrass pastures [Agropyron elongatum (Host) Beauv., = Elytrigia elongata (Host) Nevski], Lauriault et al. (2005) found no differences in stocker cattle performance grazing monoculture alfalfa and the mixture of alfalfa with tall wheatgrass. Allen et al. (1992) evaluated performance of cow–calf groups grazing mixtures of tall fescue–red clover, orchardgrass–red clover and orchardgrass–alfalfa in Virginia. They also found that pasture species mix had relatively minor effects on overall performance of cows and calves. In their study, climatic effects on forage availability appeared to be more important in affecting cattle performance.


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  		Table 7. Cow and calf performance data– initial weights, average daily gain (ADG) and gain ha–1. Values are means ± 1 SE. Letters that differ within respective response variables are significantly different (P < 0.05) using Tukey's HSD.

 
Tall fescue was one of the base species sown in each pasture and endophyte-infected fescue (E+) can adversely affect cattle performance (Read and Camp, 1986). Pastures at the Orr Center contained E+ fescue before they were renovated with endophyte-free (E–) fescue for this experiment. We monitored the potential re-infestation of E+ fescue into E– pastures and found that E+ levels remained below toxic thresholds for cattle and did not differ among the mixtures (Tracy and Renne, 2005). The similar levels of E+ fescue among mixtures may also explain why we found little difference in cattle performance among the mixtures. In addition, small differences in cattle performance may be difficult to detect using cow–calf pairs because their performance may be relatively insensitive to changes in forage availability (Aiken and Bransby, 1992). If this is true, using stocker cattle in our experiment instead of cow-calf groups might have produced different results.

Cow and calf daily gain and gain ha–1 were significantly greater in 2003 compared with other years (Table 7). Cow performance was variable but especially better in 2003. In fact, daily gains were similar (0.33 kg d–1) to growing heifers in a previous rotational stocking study at this site (Bertelsen et al., 1993). The better performance in 2003 may reflect higher forage productivity (Table 4) and lower stocking rate that year compared with 2002 (Table 5). Stocking rate has been shown to be one of the major factors that influence cattle performance (Aiken and Bransby, 1992; Hernandez Garay et al., 2004; Olson, 2004). As stocking rate increases, herbage allowance and mass declines and forage availability can limit cattle productivity. For example, Hernandez Garay et al. (2004) found that stocking rate had a greater effect than N fertilization on weaned bull performance grazing on stargrass (Cynodon nlemfuensis Vanderyst) pastures in Jamaica. The higher stocking rate in 2002 mainly resulted from extra cows that were added to graze the spring flush of forage that occurred this first year of grazing. The high herbage mass in the spring of 2002 resulted from late introduction of cattle into the pastures and probably residual N from the initial fall fertilization. Herbage mass averaged between 460 and 737 g m–2 before gazing began in May 2002.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Increasing the species richness of pastures from three to eight sown species produced few agronomic benefits in this rotationally stocked, cow–calf grazing system. Different pasture mixtures had negligible effects on both forage yield and cow–calf performance. Even if it was a desired goal, maintaining high forage species richness in pastures will be difficult because some sown species tend to decline in abundance more than others. For example, most broadleaf species, especially red clover and chicory, declined sharply after establishment. Among grasses, smooth bromegrass also showed marked declines in abundance. Tall fescue and orchardgrass generally increased or remained stable in most pastures and appeared well suited for this environment. Overall, species richness in pastures had minimal effects on forage yield and cattle performance. Compared with pasture species richness, grazing management (e.g., stocking rate) and climatic conditions more strongly influence grazing system productivity.


   ACKNOWLEDGMENTS
 
The authors wish to thank Jim Dalquist, Danny Graham, Larry Spencer, Mike Vose, and other members at the Orr Center Research facility for their help with various aspects of this study. Without their cooperation, this study would not have been possible. Dr. Ian Renne also assisted with field work. This project was supported from a USDA Hatch grant ILLU-802-369.

Received for publication April 13, 2006.


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





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