Structural Composition, Growth Stage, and Cultivar Affects on Kentucky Bluegrass Forage Yield and Nutrient Composition

Kentucky bluegrass (Poa pratensis L.) is an important turf and forage grass, yet there is little information on its forage yield and nutrient composition. This study evaluated the effect of Kentucky bluegrass cultivar (Ascot, Kenblue, Limousine, and Touchdown), growth stage (boot, anthesis, and seed ripening), and structural composition (percentage head, leaf, and stem) on forage yield and nutrient composition. Nutrient composition measurements included dry matter, crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), lignin, and 48-h in vitro true digestibility (IVTD). Tall cultivars had the greatest yield, and yield tended to be greatest at seed ripening. Structural composition varied among cultivars due to differences in cultivar height and yield. Nutrient composition was not different among cultivars despite differences in structural composition among cultivars and nutrient composition differences among structural components. Leaves were greatest in IVTD (636 g kg^-1), stems were greatest in NDF (740 g kg^-1) and ADF (430 g kg^-1), and lowest in CP (30 g kg^-1) and IVTD (455 g kg-1), and heads were lowest in ADF (269 g kg^-1) and greatest in lignin (83 g kg^-1). Nutrient level was greatest at boot and averaged 435 g kg^-1 NDF, 197 g kg^-1 ADF, 17 g kg^-1 lignin, 165 g kg^-1 CP, and 766 g kg-1 IVTD. On average between boot and anthesis, CP decreased 0.57% d^-1 in 2003 and 0.21% d^-1 in 2004, and IVTD declined 0.47% d^-1 in 2003 and 0.49% d^-1 in 2004. Nutrient level decreased as the stand aged due to an increase in structural carbohydrates and a decrease in IVTD.