Missouri Forage and Grassland Council 2000 Annual Meeting October 30-31, 2000 Lake Ozark Holiday Inn, Lake Ozark, Missouri

Warm-season grasses like big bluestem, switchgrass, and indiangrass have great potential as summer pasture grasses throughout much of the Corn Belt and Great Plains. Proper grazing management is crucial to maintain dense, productive, nutritious stands of warm-season grasses. While plant response to grazing is similar, warm-season grasses should be grazed differently than cool-season grasses. Major differences include length of rest, sensitivity to severe grazing (especially late season), and grazing before elevation of apical meristems.

Warm-season grasses like big bluestem, switchgrass, and indiangrass have great potential as summer pasture grasses throughout much of the Corn Belt and Great Plains. While cool-season grasses, such as tall fescue, smooth bromegrass, and orchardgrass are nearly dormant and unproductive during the heat of midsummer, warm-season grasses thrive under these conditions.

Warm-season grasses start growth about 4 to 6 weeks later in spring than do cool-season grasses. As a result, spring soil moisture is conserved. At least 60% of the annual growth of warm-season grasses usually occurs during June through August. In contrast, more than 60% of the growth of cool-season grasses occurs before June (Rountree et al., 1974).

Like cool-season grasses, warm-season grasses grow best on well-drained, fertile soils and they respond well to proper fertilization, weed control, and defoliation management. Warm-season grasses thrive at 30^o to 35^o C, but grow very slowly below 20^o C. They use less water than cool-season grasses to produce similar growth (Downes, 1969). They also are more efficient in nitrogen utilization (Brown, 1978) and grow better than cool-season grasses on phosphorus-deficient soils (Morris et al., 1982). Thus, warm-season grasses often are grown on soils with growth limitations because they perform better than cool-season grasses on those sites.

Switchgrass tolerates poorly drained soils, flooding, perched water tables, and salinity better than many other commonly seeded warm-season grasses (Duke, 1978). Big bluestem is more drought tolerant than other tall warm-season grasses and thus may be better adapted to excessively drained soils with low water-holding capacity. Even better adapted to these droughty sites are two mid-grasses, little bluestem, and sideoats grama, which often are seeded in mixtures with the tall warm-season grasses.

Native warm-season grasses have great potential to provide desirable summer grazing when cool-season grasses are less productive. However, warm-season grasses differ from cool-season grasses in their response to grazing. Warm-season grasses evolved under grazing, but it was intermittent so they are not well adapted to continuous stocking or close, frequent defoliation. And their nutritional characteristics provide unique challenges and opportunities for graziers. Thus, research about grazing these grasses has focused on solving these problems and identifying useful roles for warm-season grasses in livestock production systems.

Systems
Grazing research with warm-season grasses initially focused on summer gain potential and/or opportunities to use warm-season grasses in grazing systems. Early Nebraska studies showed that average daily gains (ADG) from late April through early November increased 38% when steers grazed cool-season grasses in spring and autumn and warm-season grasses during summer compared to grazing cool-season grasses season-long (Conard and Clanton, 1963). Improved season-long gains were due to a threefold increase in daily gain during summer for steers grazing warm-season grasses. Subsequent studies averaged 31% more gain per animal and 96% more gain per acre when warm-season grasses were grazed by yearling steers during summer than stockpiled smooth bromegrass (Klopfenstein and Lewis, 1988). Cows (0.94 vs 0.33 lb) and calves (2.05 vs 1.72 lb) also had higher ADG when they sequentially grazed smooth bromegrass, switchgrass, big bluestem, and smooth bromegrass again than when they grazed smooth bromegrass continuously (Ward, 1988).

In Missouri, switchgrass and caucasian bluestem produced daily and per acre gains similar to tall fescue + fescue hay without the need to harvest hay (Matches et al., 1975; Matches et al.,1982; Anderson, 1986). Summer gains of cattle often exceeded 1.0 lb/day in a region characterized by summer weight loss when endophyte-infected tall fescue was grazed alone. Similarly, Oklahoma studies with switchgrass and sand bluestem produced ADG from 0.82 to 1.37 lb (Dwyer and Elder, 1964).

Beef yearling steers gained an average of 2.0 lb/day and ranged from 1.5 to 2.4 lb/hd/day from switchgrass, big bluestem, indiangrass, and sideoats grama in South Dakota over 3 years (Krueger and Curtis, 1979). Gain per acre ranged from 100 to 131 lb. In western Iowa (Wedin and Fruehling, 1977), both switchgrass and aftermath smooth bromegrass produced slightly over 1.3 lb ADG during midsummer, but switchgrass provided more steer days of grazing (139 vs 96 d) and higher gains per acre (200 vs 132 lb). Further studies grazing smooth bromegrass and switchgrass alternately in Iowa enabled maintenance of higher stocking rates than season-long grazing of smooth bromegrass. Switchgrass produced higher ADG than smooth bromegrass (1.65 vs 1.48 lb) but had a lower carrying capacity (183 vs 205 steer days/acre (Wedin et al., 1980)).

Similar results grazing warm-season grasses alone or in grazing systems have been recorded in North Carolina (Burns et al., 1984), Pennsylvania (Fairbairn et al., 1985), West Virginia (Reid and Jung, 1985), and Illinois (Kaiser et al., 1986). In contrast, grazing studies in Wisconsin showed no advantage to sequentially grazing Kentucky bluegrass with switchgrass compared to grazing Kentucky bluegrass season-long (Smart et al., 1995). Under Wisconsin conditions, there was no slump in pasture and animal productivity during summer from Kentucky bluegrass.

Management
Until recently, most management recommendations relied on experiences grazing cool-season grasses, although there were some attempts to use deferred rotation grazing schemes similar to those employed in native rangelands (Smith and Owensby, 1978). However, current grazing research has shown that in sub-humid or semiarid regions, warm-season grasses respond differently than cool-season grasses to grazing strategies such as grazing frequency, intensity, and duration.

In Missouri, big bluestem was stocked continuously or in rotation, with rotational stocking providing either a 7-day grazing period with a 14-day rest period or 1-day grazing period with a 20-day rest period (Gerrish et al., 1994). Although rotational stocking provided more available forage than continuous stocking in all three years of the study, big bluestem virtually disappeared from all pastures and was replaced by volunteer warm-season annual grasses. An inadequate rest period was suspected to be part of the problem. Stand decline was most rapid with continuous stocking and following trampling damage during wet weather. Intake by lactating beef cows grazing these pastures and in vitro dry matter digestibility (IVDMD) of the forage consumed was greater when cows were rotated daily compared to continuous stocking; both intake and IVDMD declined from day 1 to day 7 during the 7-day grazing periods (Morrow et al., 1994).

Switchgrass was grazed at three stocking rates in Alabama using continuous stocking or an 8-paddock rotation (Maposse et al., 1995; Maposse et al., 1996). As stocking rate increased, ADG decreased in both single-year studies, primarily late in the grazing season. However, there were no differences between grazing methods.

Iowa studies have shown large advantages to intensive early stocking of switchgrass and big bluestem compared to continuous stocking (George et al., 1996). Continuous stocking began in late June or mid-July. Intensive early grazing occurred for 2 weeks or less in late May or mid-June, followed by a 4-week rest period and a second grazing period. Over 3 years, steer ADG was 2.4 vs 1.9 lb for switchgrass and 2.8 vs 2.4 lb for bluestem while gain per acre was 214 vs 77 lb for switchgrass and 160 vs 89 lb for big bluestem from rotational vs continuous stocking, respectively. Improved gains were attributed to less trampling waste with intensive early stocking and greater leaf-to-stem ratios for grazing, resulting in higher forage quality at the time of grazing.

Nebraska studies recently compared continuous to rotational stocking at 3 stocking rates during a 6-year grazing trial using a 5-species mixture of warm-season grasses (Anderson, 1996a;1999). Average daily gains tended to decline as stocking rate increased, but the decline was steepest with continuous stocking. During the first 2 years, gains per hectare were greatest with continuous stocking, but rotational stocking produced progressively higher gains per hectare in relation to continuous stocking in later years, especially as stocking rate increased. Rotational stocking extended the grazing season slightly and gains tended to be influenced less by stocking rate.

Tall and medium height warm-season grasses need lengthy rest periods (40+ days) following severe grazing. Rotational grazing is essential if livestock reduce stubble to less than 8 inches and consume nearly all the leaves. If stubble height can be maintained between 10 and 16 inches, lengthy grazing periods or continuous stocking can be effective. Pastures should not be grazed shorter than 8 inches after early September.

Stem management is nearly as important as leaf management with tall warm-season grasses. Stems become unpalatable, have low digestibility and protein, and reduce intake. Removing the shoot apices by grazing during jointing and stem elongation will reduce mature stem development while stimulating leaf growth and consumption.

Stems elongate and plants mature at different times for different warm-season grasses (Branson, 1953). Switchgrass develops stems 2 to 3 weeks earlier than many warm-season grasses; indiangrass is one of the latest. When several warm-season grasses are mixed together in the same pasture, switchgrass becomes stemmy and less palatable earlier in summer than other warm-season grasses. Livestock refuse to eat switchgrass and selectively graze less stemmy grasses, preferring big bluestem. Palatable grasses will be overgrazed while switchgrass is underused in the same pasture.

Because switchgrass has such unique affects on grazing, management will be discussed using three broad categories: pure switchgrass, mixed stands with switchgrass, and mixed stands without switchgrass.

Pure switchgrass. Switchgrass must be grazed before seedheads develop. Before seedheads develop, forage quality is high and palatability good. After seedheads emerge, nutrient levels become low and switchgrass becomes unpalatable. Animals eat mature switchgrass reluctantly and may refuse it entirely if other feed is available (Mitchell et al., 1994).

Grazing of switchgrass must begin when it becomes ready to graze, regardless of how much grazing potential remains on cool-season pastures. It is better to graze switchgrass when it is ready and then graze the remaining cool-season grass later in the summer than to finish grazing the cool-season grass first and let switchgrass become stemmy. If switchgrass becomes stemmy before grazing begins, it should be cut for hay and the regrowth grazed about 45 days later.

Several options are available for grazing switchgrass. One option is to begin grazing when switchgrass is 8 to 10 inches tall by stocking the pasture so livestock will consume switchgrass at the same rate that it grows. Livestock will graze off the tops of switchgrass plants rather uniformly if coarse stems have not started to form. Plant height should be kept between 8 and 16 inches for 6 to 8 weeks, then remove livestock for 30 to 45 days. Regrowth may be grazed (it may be fairly stemmy with good growing conditions) to a stubble height no shorter than 8 inches. Stocking switchgrass too heavily and moving animals to other pastures sooner than planned is better than stocking too lightly and having abundant seedheads develop.

It is difficult to predict switchgrass growth rate and to stock it to maintain 8 to 16 inches of stubble. Thus, an easier grazing method is to begin grazing when switchgrass is 10 to 12 inches tall and stock heavily for two to three weeks until there is about a 4- to 6-inch stubble. Then livestock should be removed and switchgrass allowed to recover for 40 or more days. If at least 12 inches of regrowth occurs, it may be grazed again but to no less than an 8-inch stubble height. Grazing that removes young stems in early summer will reduce and delay switchgrass heading and provide higher quality regrowth later in the grazing season.

Switchgrass is not good as the only forage source for all of June, July, and August. Use switchgrass during just two of these three summer months. Either graze switchgrass uniformly in June and July or graze completely in June and graze regrowth in August. Avoid stemmy, mature growth.

Mixed stands with switchgrass. The biggest challenge in these stands is reducing selective grazing so switchgrass will be used and more palatable grasses will not be overgrazed (Anderson, 1996b).

Selective grazing can be controlled by management. If only one warm-season pasture is available, grazing options are similar to pure switchgrass. When grass gets 8 to 10 inches tall, stock the pasture so livestock consume growth about as fast as it grows. Livestock will graze fairly evenly for about 3 or 4 weeks until switchgrass becomes unpalatable. Grazing usually can continue another 2 or 3 weeks with yearlings gaining 1.5 to 2.5 lb/day during this period.

At this point, if 8 or more inches of growth remain, grazing can continue until stubble height is only 4 to 6 inches. Then end grazing for the year. Alternatively, the warm-season grass pasture can be rested for at least 4 weeks, followed by light grazing to no shorter than an 8-inch stubble. If stubble is shorter than 8 inches at this point, rest the pasture for 4 weeks plus 1 more week for every inch of stubble below 8 inches. Then regrowth can be grazed lightly to no shorter than an 8-inch stubble.

The other option for a single mixed warm-season pasture is to stock heavily enough when grass gets 12 to 16 inches tall to reduce growth to 6 inches of stubble within 3 weeks. This grazing must begin early and use switchgrass before stems develop. Growth remaining on cool-season pasture should be left if necessary to accomplish this early grazing. Then return to cool-season pastures for about 6 weeks to use their remaining growth and permit warm-season grasses to regrow. The warm-season regrowth can be grazed until either cool-season grasses are ready for fall use or until warm-season grass stubble is 8 inches.

A better way to use mixed stands is to rotationally graze. Alternate which paddock is grazed first each year. Grazing should begin when grass is 8 to 10 inches tall. Each paddock should be grazed only a few days so that livestock begin grazing the final paddock as switchgrass is jointing, before the boot stage. Graze this last paddock until 6 inches of stubble remain before continuing the rotation. Then graze each of the rest of the paddocks to about 6 inches of stubble to reduce seedstalks in regrowth. As switchgrass begins to form seedstalks that are not grazed, use the palatable grasses to judge stubble height. All paddocks grazed to 6-inch stubble should rest 40+ days before regrazing, leaving at least 8 inches of stubble going into winter.

Mixed stands without switchgrass. Because most other warm-season grasses form seedstalks later than switchgrass, they may be ready to graze at a more convenient time than switchgrass, relative to the growth of cool-season pastures. Also, more flexibility is available when switchgrass is not in the stand. Still, good management remains necessary to maintain good grass and animal performance.

Mixed stands can be continuously stocked all summer if livestock begin grazing when grass is 10 to 12 inches tall, grazing is uniform (unlikely in large pastures), and stocking rate or adjustments in animal numbers maintain a consistent amount of leaf area and stubble. Be sure at least 6 to 8 inches of stubble remain for winter.

Mixed stands are well suited for rotational stocking, which is easier than trying to match stocking rate with growth rate and also provides more uniform grazing. Begin when grass is 8 to 12 inches tall.

One method of rotational stocking involves grazing each paddock no longer than two to three weeks to a stubble height about equal to one-half the original plant height. This method works well for a system with two to four paddocks. Another method that works well with just a few paddocks is heavily grazing each paddock to 4 to 6 inches. Then rest each paddock for at least 40 days, often longer. Delay further grazing of any paddock until regrowth is at least 12 inches tall. Remove livestock during subsequent grazing periods to leave an average stubble height of at least 6 inches. Conclude grazing so at least 6 to 8 inches of stubble will be on each paddock going into winter. With 6 or more paddocks, graze each paddock lightly at first, removing no more than 25% of the growth in 1 to 3 days. Complete the first rotation within 2 or 3 weeks. The next grazing can be done the same way, but as seedstalks begin to develop, graze to a shorter 6-inch stubble. Adjust rest periods so paddocks grazed short receive at least 40 days of recovery; paddocks with 10 or more inches of stubble may need only 25 to 30 days before regrazing.

Wedin, W.F., and W. Fruehling. 1977. Smooth bromegrass vs. switchgrass for midsummer pasture. p. 9-11. In Ann. Prog. Rept., Western Res. Cntr, Castana, IA. ORC 77-10. Iowa State Univ, Ames.