Proc. 56^th Southern Pasture and Forage Crop Improvement Conference, Springdale, AR April 21-22, 2001

Production and Grazing Management for Eastern Gamagrass

Robert L. Gillen bgillen@spa.ars.usda.gov
USDA-ARS
Southern Plains Range Research Station
Woodward, Oklahoma

Eastern gamagrass (Tripsacum dactyloides L.) is a tall, warm-season native grass found throughout the southeastern USA. Eastern gamagrass was once fairly common but has declined due to improper grazing management and conversion of its habitat to alternative land uses. The high production potential of this grass has prompted interest in its use for many years. Most of the prior research on eastern gamagrass has focused on genetics and breeding. Few studies are available on production and grazing management.

Defoliation Management

Palatability. Virtually all research reports and anecdotal accounts extol the palatability of eastern gamagrass. This is surprising given the coarseness of the herbage. One explanation is the high proportion of leaf material versus stem for eastern gamagrass compared to other tall grasses. Certainly, high palatability is a desirable trait for a forage grass that, in some ways, helps to simplify grazing management. Conversely, excellent palatability may cause more selective grazing in mixed-species pastures. The coarse nature of the grass also causes problems in monocultures because it promotes the normal selection of regrowth herbage over ungrazed herbage. Advisors uniformly suggest some form of rotational stocking to maintain mixed-species stands as well as monocultures. As with any forage, there are limits on the palatability of eastern gamagrass and other grasses may be selectively grazed within eastern gamagrass pastures. Two examples are johnsongrass (Sorghum halepense (L.) Pers.) and grasses with finer leaves such as Old World bluestem (Bothriochloa ischaemum (L.) Keng var. ischaemum) or crabgrass (Digitaria sanguinalis (L.) Scop.). The finer leaved grasses are especially preferred in late summer as the eastern gamagrass matures.

Grazing Readiness. Eastern gamagrass begins growth in spring somewhat earlier than other native warm-season grasses. Sufficient growth for grazing is usually present in late April to early May. Dates for initiation of grazing at 2 distant sites were May 1 in North Carolina to May 10 in western Oklahoma.

Intensity and Frequency of Defoliation. Most management recommendations for the intensity and frequency of grazing on eastern gamagrass are based on adaptive management rather than controlled research studies. Recommendations generally assume some sort of rotational stocking.

A minimum stubble height of 6 to 8 inches is widely recommended. The application of this guideline is relatively simple for hay production although the height is higher than that used for most other forage crops. Under grazing, the average stubble height must be considerably higher to maintain a minimum stubble height of 6 to 8 inches on most of the plants in a stand.

Rest periods of 28 to 45 days have been recommended under rotational stocking. However, evidence suggests that 28-day rest periods may not be long enough to maintain vigor. Fick (1993) clipped individual plants at 6 to 8 inches at early heading with follow-up clipping at 28 or 42-day intervals. Plants clipped at the more frequent interval lost vigor and many were almost dead after 3 years of treatment. In Missouri, 28-day rest periods produced less hay than 42-day rest periods in 4 of 6 comparisons (Brejda et al. 1996). Under drought conditions, rest periods were extended to 56 days. Brakie (1998) reported yields of 8640, 10700, and 13240 lb acre^-1 when eastern gamagrass was harvested at 30, 45, or 60-day intervals, respectively, in East Texas. Rest periods of 40 to 45 days appear to be optimal for maintenance of stand vigor and forage quality. A 45-day rest period prior to killing frost is recommended to maintain stand health.

Continuous and rotational stocking of eastern gamagrass were compared in western Oklahoma. Rest periods under rotational stocking averaged 30 days. Stubble height at the end of the rotational grazing periods averaged 13 to 20 inches. Continuous stocking thinned the eastern gamagrass because of excessive spot grazing and weakening of individual plants. Cover of live crowns of eastern gamagrass decreased from 58% to 44% in the continuously stocked pastures even though grazing was terminated 40 days early in the last 2 years of the 3-year study (Gillen, unpublished data). Cover of live crowns of eastern gamagrass in the rotationally stocked pastures also decreased but only from 56% to 50%. Although the stands of eastern gamagrass in the rotationally stocked pastures remained uniform and appeared to be healthy, a somewhat longer rest period may be needed for long-term stand maintenance.

Growth Rates. Height growth of eastern gamagrass is quite high in late spring with peak growth rates of 1 to 2 inches per day. Growth rates steadily decline throughout the summer with little or no growth occurring in September and October. This is a common pattern for native warm-season grasses. It should be noted that these observations were made on ‘Pete’ eastern gamagrass, a cultivar of northern origins. Germplasm of eastern gamagrass from more southerly locations appears to sustain rapid growth rates over a longer period of time.

Seasonal forage accumulation mirrored height growth in western Oklahoma. Forage accumulation was concentrated in the first 6 to 8 weeks of the growing season. Accumulation rates were linear at 52 to 99 lb acre^-1 day^-1 over a 25-day period in May and June (Gillen, unpublished data).

Forage Production

Forage production of eastern gamagrass has ranged from 7110 lb acre^-1 in western Oklahoma to 15730 lb acre^-1in southern Illinois (Faix et al. 1980). Brakie (1998) reported large differences in forage production between accessions. In that East Texas study, accessions from Texas produced up to 3 times more forage than ‘Pete’, a cultivar of northern origins.

Eastern gamagrass responds well to nitrogen (N) fertilization. The N conversion rate, the ratio of lb additional forage produced per lb N applied, ranged from 0 to 44 with an average of 23 for the first 100 lb of N applied per acre in northern Missouri (Brejda et al. 1996). For the second 100 lb increment of N applied, the conversion rate ranged from 0 to 38 with an average of 15. The responses were highly dependent on site, cutting interval, and weather. In East Texas, the response of eastern gamagrass production to N application was curvilinear with peak forage production at 370 to 520 lb N acre^-1 (Brakie 1998). The conversion rate declined as the application rate increased (Fig. 1). At 100 lb N acre^-1, the N conversion rate averaged 28 but at 300 lb N acre^-1 the conversion rate averaged 12. The recommended rate of application was 250 lb N acre^-1 year^-1. In areas of lower precipitation, operational rates of N application have been 70 to 150 lb N acre^-1 year^-1.

Nutritive Value

Eastern gamagrass exhibits a seasonal cycle of nutritive value typical of warm-season grasses. Nutritive value of eastern gamagrass is high during early growth with crude protein commonly above 15% and in vitro dry matter digestibility (IVDMD) above 65% (Gillen et al. 1999). Nutritive value declines rapidly and falls below 8% crude protein by mid July (Fig. 2). By August, nutritive values are 6 to 7% for crude protein and 42 to 47% for IVDMD (Aiken 1997, Gillen et al. 1999). If forage allowance is adequate, however, actual diets may be substantially higher in nutritive value. Burns et al. (1992) reported diet crude protein levels of 19.5% and 16.5% in May and July, respectively, and IVDMD levels of 77% and 69% for the same months. Crude protein levels in clipped forage were not different between continuously and rotationally stocked pastures in Oklahoma (Fig. 2; Gillen, unpublished data). Under haying, crude protein levels remain relatively high as the season progresses because of the uniform stimulation of regrowth. Crude protein ranged from 10.3 to 13.7% over 3 harvests and 2 years when harvested on a 42-day schedule (Brejda et al. 1996).

Season of Use and Stocking Rate

All published research on eastern gamagrass has utilized growing beef cattle and grazing in the growing season. Anecdotal reports also discuss utilization with cows and calves. Use of eastern gamagrass in the dormant season is feasible although, as with other warm-season grasses, nutritive value is likely to be low. Supplementation would probably be required to support maintenance or slight gains. One caution with dormant season use is that eastern gamagrass tends to lodge as the season progresses. This could cause some difficulty in efficient harvest by grazing later in the dormant season.

Stocking rates on eastern gamagrass have ranged from 67 to 170 animal-unit-days (AUD) acre^-1 (Table 1). The grazing systems using steers likely could have produced additional grazing days during the dormant season. Stocking rates will vary depending on site, fertilization, and grazing management. A comparison of the stocking rates from Oklahoma illustrates the large impact of site within the same geographical region. The bottomland site produced 73% more AUD acre^-1 than the upland site.

Animal Performance

In Arkansas, Aiken (1997) stocked yearling steers continuously at 3 stocking densities until a target canopy height (18 to 24 inches) was reached. Initial stocking densities were 1.2, 2, or 3 steers acre^-1 and the respective grazing seasons were 140, 116, and 86 days, respectively. Average daily gains (ADG) ranged from 1.6 lb head^-1 day^-1 in early May to no gain in late September. There were no differences in ADG among treatments, probably because forage allowance was relatively high for all treatments. Gain per acre increased dramatically, from 195 to 420 lb acre^-1, as stocking density increased (Table 1).

On an upland loamy site in western Oklahoma, eastern gamagrass was grazed in conjunction with Old World bluestem. Eastern gamagrass was grazed in May and August while Old World bluestem was grazed in June and July. Average daily gains on eastern gamagrass were 2.65 lb head^-1 day^-1 in May and 1.32 lb head^-1 day^-1 in August (Fig 3). Total beef production from eastern gamagrass was 199 lb acre^-1 (Gillen et al. 1999).

Rotational and continuous stocking on eastern gamagrass were compared on a bottomland site in western Oklahoma (Gillen, unpublished data). Rotational stocking used 4 paddocks, 10-day graze periods, and 30 day rest periods. Average daily gain ranged from 2.72 lb head^-1 day^-1 in May to 1.45 lb head^-1 day^-1 in August (Fig. 3). Average daily gain was not different between grazing treatments. Beef production was 395 lb acre^-1 under rotational stocking and 333 lb acre^-1 under continuous stocking. Beef production was higher under rotational stocking because continuous stocking was terminated about 40 days earlier in 2 of 3 years due to severe selective grazing.

In North Carolina, eastern gamagrass was stocked continuously from early May to late August (Burns et al. 1992). Stocking density was adjusted to maintain a stubble height of 8 to 13 inches. Average daily gain over the last two-thirds of the grazing period was 1.8 lb head^-1 day^-1. Gain was not correlated with standing crop or canopy height. It appears that grazing management that maintains minimum stubble heights for plant health will produce maximum average daily gains. In this study, ADG from eastern gamagrass were higher than gains from either bermudagrass (Cynodon dactylon (L.C. Rich) or flaccidgrass (Pennisetum flaccidum Griseb.).

In summary, ADG of stocker cattle grazing eastern gamagrass ranged from 2.5 to 2.7 lb head^-1 day^-1 early in the growing season to 1.0 to 1.5 lb head^-1 day^-1 in August. Overall seasonal gains were 1.5 to 2.0 lb head^-1 day^-1. The seasonal pattern of these gains is similar to other warm-season pasture grasses.

Summary and Conclusions

Eastern gamagrass has several desirable qualities including high palatability, relatively early green-up, and high production potential. Forage nutritive value is similar to other warm-season pasture grasses with high nutritive value for about 45 days followed by a steady decline to moderate to low values late in the growth cycle. The coarse nature of the grass promotes selective grazing on previously grazed plants under continuous stocking. Efficient forage use and stand maintenance require rotational stocking with 30 to 45 day rest periods or high density grazing over a shorter season. Due to the expense and time required to establish eastern gamagrass, producers should be committed to upper-level management, including proper fertilization and grazing management, to take advantage of its positive characteristics and ensure optimum returns.

Literature Cited

Aiken, G. E. 1997. Temporal effects on steer performance and nutritive values for eastern gamagrass grazed continuously for different durations. J. Anim. Sci. 75:803-808.

Brakie, M.R. 1998. Yield and quality of eastern gamagrass selections as affected by clipping interval and N rates. M.S. Thesis, Stephen F. Austin State University, Nacogdoches, Texas.

Brejda, J.J., J.R. Brown, T.E. Lorenz, J. Henry, J.L. Reid, and S.R. Lowry. 1996. Eastern gamagrass responses to different harvest intervals and nitrogen rates in northern Missouri. J. Prod. Agr. 9:130-135.

Burns, J. C., D. S. Fisher, K. R. Pond, and D. H. Timothy. 1992. Diet characteristics, digesta kinetics, and dry matter intake of steers grazing eastern gamagrass. J. Anim. Sci. 70:1251-1261.

Faix, J. J., C. J. Kaiser, and F. C. Hinds. 1980. Quality, yield, and survival of Asiatic bluestems and an eastern gamagrass in southern Illinois. J. Range Manage. 33:388-390.

Fick, W.H. 1993. Production and quality in eastern gamagrass, p. 37. In: USDA-SCS. 1993. Proceedings eastern gamagrass workshop. USDA-SCS Midwest Technical Center, Lincoln, Neb.

Gillen, R.L., W.A. Berg, C.L. Dewald, and P.L. Sims. 1999. Sequence grazing systems on the southern plains. J. Range Manage. 52:583-589.

Polk, D.B., and W.L. Adcock. 1964. Eastern gamagrass. The Cattleman 50(9):82-84.