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 6-wk 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.