USDA, ARS, Southern Plains Range Research Station, Woodward, OK

Eastern gamagrass, Tripsacum dactyloides (L.)L is a robust, perennial warm season bunchgrass native from Oklahoma and the Texas panhandle to the east coast. This grass was once abundant on hundreds of thousands of acres but it is now common only in areas protected from grazing because of its high palatability to livestock.

USE AND POTENTIAL

Eastern gamagrass can be developed into an important component of forage and beef production systems. It produces forage earlier in the spring than most other warm-season grasses and can be used to allow deferment of rangeland at this critical growth period. It has high potential for green-chop, hay or silage production or for intensively managed pastures.

Gamagrass flourishes under dryland conditions in the southeastern U.S. where annual precipitation exceeds 35 inches. Respectable production can be achieved on good soils in regions with 25 inches annual precipitation. In the semi-arid regions of the southern great plains, gamagrass should be a good substitute for forage sorghums, sudans and millets under supplemental irrigation. The perenniality of gamagrass offers advantages over these annual forages of lower cultural energy requirements, less erosion potential, and lower production costs.

PLANT MATERIALS AVAILABLE

The released cultivars of gamagrass are 'Pete' and ‘Iuka IV’. ‘Pete’ was released in 1988 by the Soil Conservation Service and Agricultural Research Service in cooperation with the Kansas and Oklahoma Agricultural Experiment Stations. 'Pete' was developed from seed composites of 70 native populations from Kansas and Oklahoma followed by three generations of advancement by combine harvest and replanting of open pollinated seed. Under irrigation at Woodward, Oklahoma ‘Pete’ (prerelease tested under the designation PMK-24) produced forage yields of 2 tons dry matter per acre (DM/A) during the establishment year and 8-10 tons DM/A the second and third year. In vitro dry matter digestibility (IVDMD) averaged 63 percent with harvests at 45 day intervals during the growing season. ‘Iuka IV’ was recently released on the basis of easy establishment by seed and higher productivity. ‘Pete’ non-certified seed of PMK-24 and ‘Iuka IV’ are commercially available.

PLANTING RATES. Good stands of gamagrass have been obtained using 10 pounds of high quality seed per acre. At present there is no standard ASA testing procedure to determine germination, and laboratory tests may be misleading because of seed dormancy characteristics. Good quality seed usually has about 6000 seed units per pound and higher seeding rates (12-15 lbs/A) will be needed if seed units per pound exceeds 6000.

PLANTING DEPTH. Seed should be planted 1 to 1-1/2 inches deep. Planting in deep furrows in soils subject to washing should be avoided as seed can be covered too deep. Plantings shallower than 1" will have less favorable moisture-seed relations and emergence may be delayed. As with all grasses, a firm seedbed is desirable.

PLANTING DATE. Dryland plantings in western Oklahoma should be made in mid-winter to allow the seed to undergo a natural pre-chill treatment in the soil. This is necessary to break seed dormancy. The use of artificially pre-chilled seed in dryland plantings is not recommended as seed will regain dormancy if they dry out before germinating. Mid-January to mid-February plantings appear to be more effective than earlier or later plantings.

Irrigated plantings can be accomplished with artificially pre-chilled seed (35-45 F for 6 weeks). Planting in mid-April through May has resulted in successful stands provided the soil is kept moist until the seed germinates.

PLANTING EQUIPMENT. Row planters (corn, cotton, peanut, etc.) are easily adjusted to plant gamagrass seed in rows. For seed production we recommend rows 40" to 48" wide and 4-6 seed planted per foot of row. Row plantings can be cultivated in the early stages for weed control. Solid plantings can be made with most grain drills using the oat side of the drill feeder. Solid plantings offer no advantage over row plantings unless the seeding rate is doubled and this may be cost prohibitive.

NURSE CROPS. The use of a small grain nurse crop may be desirable if a soil erosion potential exists. Gamagrass seed can be planted in mid-winter into fall planted small grains by adjusting the shovels or discs on the row planter to create a shallow (1") narrow (6-10") furrow to remove vegetation from and adjacent to the planted seed row. If a nurse crop is used it must be removed by mid-April to reduce competition to the gamagrass.

NITROGEN FERTILIZATION. Nitrogen rates of 100, 250 and 400 lbs N/acre applied in split applications on April 1, June 1 and July 15 were compared in a three year study at Woodward, OK. The 250 lb N/A rate gave significantly higher forage yields with an economical advantage over the 100 lb N/A rate. The 400 lb N/A rate produced sightly more forage than the 250 lb N/A rate but was not economical at today's hay and fertilizer prices.

HAYING FREQUENCY. Hay yield and quality were compared using 30 day (June 1, July 1, August 1 and September 1), 45 day (June 1, July 15, and September 1) and 60 day (June 1 and August 1) clipping frequencies. To maintain the stand, clipping height must be no closer than 6-8 inches high. Closer clipping will reduce the yield, and subsequently the stand. As would be expected, the lowest production and highest quality hay was obtained from the 30 day clipping intervals. The 60 day clipping interval resulted in the highest forage production, but forage quality was reduced. The 45 day clipping interval was intermediate in forage production and produced more total digestible nutrients per acre than the other treatments.

GRAZING GAMAGRASS

Experience by livestock grazers over the past 150 years has shown that gamagrass will be eradicated from pastures unless careful controlled grazing practices are followed. Gamagrass is so palatable to livestock that it is one of the first grasses to be eliminated under continuous grazing. Gamagrass regrowth has been measured at a rate of 2 inches per day. This new regrowth is tender, nutritious and greatly preferred by livestock compared to older forage. This leads to spot grazing with the same plants being defoliated almost daily resulting in reduced plant vigor and eventual death.  Grazing must be controlled to maintain a minimum 6-8 inch stubble height. Closer grazing or clipping will reduce plant vigor and eventually reduce the stand.  Short duration, high intensity rotation programs to limit the cattle to 4-6 days per pasture with at least 8 pastures would give each pasture a 28 to 42 day rest period to recuperate.

DRYLAND GRAZING TRIALS. A non-irrigated study at Woodward evaluated complementary grazing of ‘Pete’ eastern gamagrass and Old World bluestem. Eastern gamagrass was grazed by steers in May, Old World bluestem in June through mid-July, and then the steers were returned to the eastern gamagrass. The grasses received 60 pounds of N/acre/year and were burned each year in early spring. Under this complementary grazing system, yearling steers gained 2.2 lb/day over 100 days. Gains ranged from 2.6 lb/day in May to 1.3 lb/day in August.