EVALUATING NONSTRUCTURAL CARBOHYDRATE VARIATION OF COOL-SEASON GRASSES BASED ON GENOTYPE, MANAGEMENT AND ENVIRONMENT

Understanding how nonstructural carbohydrates fluctuate in pastures and being able to quantify them is an essential component in successfully managing grazing animals that may require high or low nonstructural carbohydrate diets. The objectives of this study were 1) to evaluate the effects of genotype, management, and environment on water-soluble carbohydrates (WSC) and ethanol-soluble carbohydrates (ESC) in cool-season grass pastures in central Kentucky, and 2) to develop near-infrared reflectance spectroscopy (NIRS) equations to predict WSC and ESC in cool-season grasses. Ten cool-season grass cultivars consisting of Kentucky bluegrass, tall fescue, orchardgrass and perennial ryegrass were sampled in the morning and afternoon every two to four weeks during the growing season from the University of Kentucky Research Farm in Lexington, KY. Samples were immediately flash frozen after sampling, freeze dried, ground, and scanned into FOSS 6500 NIRS with ISIscan software. WSC and ESC were determined using colorimetric phenol-sulfuric acid assays on a subset of samples and served as the basis for NIRS calibration. NIRS equations for both WSC and ESC accurately predicted wet chemistry values between 2% and 20%. Significant species and diurnal effects were observed for WSC and ESC. WSC and ESC concentrations were typically highest in the afternoon and lowest in the morning. Perennial ryegrass was the highest WSC accumulating species, followed by tall fescue, KY bluegrass, and orchardgrass. The effect of nitrogen fertility on WSC and ESC was inconsistent among harvest dates and cultivars. In conclusion, WSC and ESC in cool-season grasses are dependent on an interaction of factors including genotype, management and environment