William F. Anderson, Crop Genetics and Breeding Research Unit, USDA-ARS, Tifton, GA and Freddie Cheek, USDA/ARS, Tifton, GA
More efficient use of nitrogen fertilizer is needed for forage bermudagrass. Fifty forage bermudagrass genotypes were selected from a bermudagrass core collection developed at Tifton, GA to determine nitrogen-use efficiency over three years. Tests were conducted by establishing plugs in 30 cm diameter and 30 cm deep corrugated tubing. Each genotype was given either 50 kg ha-1 equivalent N or 200 kg ha-1 equivalent N plus 40 kg ha-1 P and 100 kg ha-1 K in each year and replicated 4 times. Plots were harvested five times in year one and four times in years two and three. Dry matter yield and fiber quality were measured for each plot. Significant yield reduction in the lower N rate was observed starting at the third harvest in year one. Total average yield reductions in year one was 35%, and in years two and three, 78% and 73% reductions, respectively. PI 288217, PI 290660, and experimental cross 77-59 were the most N-use efficient though CC II was not significantly lower. Nitrogen content averaged 2.4% lower for the 50 kg ha-1 N (9.8% vs. 7.4%) with differences among entries. Fiber data will also be presented. This information can now be used to direct breeding efforts for improvements in N-use efficiency in forage bermudagrass.