Eastern Gamagrass Responses to Different Harvest Intervals and Nitrogen Rates in Northern Missouri

Eastern gamagrass [Tripsacum dactyloides (L.) L.] is a native perennial warm-season grass with the potential to produce high yields of high quality forage. There is, however, little information on the response of eastern gamagrass to different harvest intervals and N rates. The objective of this research was to evaluate the forage yield, crude protein concentration, and total N removal by eastern gamagrass using different harvest intervals and N rates at two sites in northern Missouri. At Elsberry and Clifton Hill, MO, established stands of ‘PMK-24’ eastern gamagrass were burned prior to green-up each spring. Individual plots were randomly assigned either a 4- or 6-wk harvest interval and five N rates (0, 50, 100, 150, or 200 lb N/acre) as ammonium nitrate and were evaluated in each harvest interval. In 1991 and 1992, total N and crude protein concentrations were determined on harvested forage and total N removal was estimated. Total forage yields were greater with the 6- than the 4-wk harvest interval at Elsberry all 3 yr, and in 1 of 3 yr at Clifton Hill. In 1991, total forage yields did not increase with N rate with either harvest interval at Elsberry, nor the 6-wk harvest interval at Clifton Hill. In 1992 and 1993, total forage yields increased linearly with N rate at Clifton Hill, and curvilinearly with N rate at Elsberry. Forage crude protein concentrations were consistently greater with the 4- than the 6wk harvest interval at both sites in 1991 and 1992. In general, forage crude protein concentrations increased linearly with N rate with both harvest intervals. In 1991, up to 200 lb N/acre was removed with the harvested forage at both sites. Total N removal increased linearly with N rate with both harvest intervals in 1991 and 1992 at Clifton Hill, but total N removal was variable at Elsberry. For grazing, a 4-wk harvest interval will provide animals with higher protein forage. For hay production, a 6-wk harvest interval may provide greater forage yields with fewer harvests. Research QuestionEastern gamagrass is a native perennial warm-season grass with the potential to produce high yields of high quality forage with multiple harvests during the growing season. Warm-season grass forage yield and crude protein concentration can be increased by N fertilization. With multiple forage harvests, greater N rates may be needed to maintain high forage yields and crude protein concentrations. There is, however, little information on eastern gamagrass forage yield, protein concentration, or N removal under different harvest intervals and N fertilization rates. The objective of this research was to determine appropriate harvest intervals and N rates for eastern gamagrass in northern Missouri. Literature SummaryIn southern Illinois, eastern gamagrass forage yields ranged from 6690 to 21 720 lb/acre, and in northwestern Oklahoma, forage yields ranged from 14 020 to 20 290 lb/acre with multiple harvests taken during the growing season. Crude protein content of eastern gamagrass is high for a warm-season grass ranging from 9.1 to 13.8% for hay and silage. In North Carolina, the diet of steers had a crude protein content of 16.5% when grazing eastern gamagrass fertilized with 120 lb N/acre, and the animals produced greater average daily gain than steers grazing either flaccidgrass or Tifton 44 bermudagrass. The high yield potential and crude protein content of eastern gamagrass forage suggest that eastern gamagrass may have high N requirements. However, there is little information on appropriate harvest intervals and N rates for eastern gamagrass under multiple forage harvests. Study DescriptionThe research was conducted using a 3-yr-old stand of ‘PMK-24’ eastern gamagrass established on a Chequest silty clay loam soil near Elsberry, MO, and a 6yr-old stand of ‘PMK-24’ eastern gamagrass established on a Piopolis silty clay loam soil near Clifton Hill, MO. The stands were burned each spring prior to green-up, divided into 10 whole-plots and randomly assigned 4- or 6-wk harvest intervals. Each whole-plot was subdivided into five subplots and randomly assigned N treatments equivalent to 0, 50, 100,150, or 200 lb N/acre. In 1991 and 1992, the harvested forage was analyzed for total N and crude protein concentrations and total N removal were estimated. Applied QuestionsWhat harvest intervals and N fertilization rates will provide optimum eastern gamagrass forage yields, crude protein concentrations, and N uptake with multiple harvests? Eastern gamagrass forage yields were greater with the 6- than the 4-wk harvest interval all 3 yr at Elsberry, and in 1 of 3 yr at Clifton Hill, with no difference between the two harvests intervals at Clifton Hill the two other years. In 1991, eastern gamagrass forage yields did not respond to increasing rates of N with either harvest interval at Elsberry, or with the 6-wk harvest interval at Clifton Hill. In 1992 and 1993, eastern gamagrass forage yields peaked near the maximum N rate tested (200 lb N/acre) for both harvest intervals at Elsberry, but increased linearly with N rate at Clifton Hill. Eastern gamagrass forage crude protein concentrations were consistently greater with each 4-wk than each 6-wk harvest, due to the greater maturity of the forage at each 6-wk harvest. In general, forage crude protein concentrations declined with each successive 4- and 6-wk harvest. Forage Crude protein concentrations increased linearly with N rate for most 4- and 6-wk harvests at both sites. In 1991, up to 200 lb N/acre was removed with the harvested forage at both sites. Total N removal increased with N rate with both harvest intervals both years at Clifton Hill, but was highly variable at Elsberry. RecommendationsEastern gamagrass forage yields and crude protein concentrations responded to increasing rates of N 2 out of 3 yr. However, the different forage yield responses to increasing rates of N at Elsberry and Clifton Hill indicate that N recommendations for optimal eastern gamagrass forage production may have to be site specific, and will depend upon the cost of different N sources and value of additional forage produced. Use of a 4- or 6-wk harvest frequency will depend upon the producer's objective. Harvesting at 4-wk intervals will result in greater crude protein concentrations, but may also result in lower forage yields. If precipitation is adequate, harvesting eastern gamagrass at the more frequent 4-wk intervals could work well in a rest-rotation grazing system since it would provide the grazing animals with a higher protein forage. For hay production for feeding nonlactating cattle, or during periods of below normal precipitation, a 6-wk harvest interval is recommended because it will result in greater forage yields with fewer trips to the field with the harvesting equipment, and place less stress on the plants.