William Anderson and Freddie Cheek, USDA ARS, Tifton, GA
Bermudagrass is the primary perennial grass forage for Southern United States. Most fertilization recommendations for forage bermudagrass (Cynodon dactylon L.) are based on extensive research with ‘Coastal’ bermudagrass which is grown throughout the Southeastern United States since its release in 1943. ‘Tifton 85’, which is phenotypically quite different than Coastal, is now being grown on increasing acreage due to higher yields and better forage quality. A 4-year study was conducted at two sites for Tifton 85 to determine the effects of six nitrogen rates and three phosphorus/potassium levels on dry matter yields, nitrogen uptake and forage quality. N rates ranged from 200 to 700 lbs/acre. The three sub-plot treatments were P-K applications at 50%, 100%, and 150% of plant uptake. Plots were harvested at 5 week intervals over three years. Dry matter yields responded to nitrogen levels significantly in all years up to 400 lbs/acre, predominantly in the first and last of five clippings. Yield differences among P-K treatments were observed in only the third and fourth year of the study. There were no significant effects among N-P-K treatments on soil nitrogen or carbon; however, there were location effects on the upper 12 inches of soil which caused differential responses to nitrogen application between locations of Tifton 85. An improvement of digestibility occurred up to 500 lbs N/acre. A linear increase in IVDMD occurred with increased yield and with increased forage nitrogen.