Daily carbohydrate accumulation in eight tall fescue cultivars

Eight cultivars of tall fescue (Lolium arundinaceum Schreb., S.J. Darbyshire 1⁄4 Festuca arundinacea Schreb.), Barcel, Kenhy, Kentucky-31, Missouri-96, Mozark, Stargrazer, C-1 (an experimental selection), and HiMag, were sampled at 2-h intervals during daylight on four cutting dates. Cultivars varied in concentrations of carbohydrate fractions but accumulation rates were not different. Daily mean total non-structural carbohydrate (TNC) concentrations for cutting dates in May, July, August and September declined from 239 to 231, 143 and 120 g TNC kg adjusted dry weight (ADW) respectively. Concentrations of fructans were highest in July but sucrose, glucose and starch concentrations were highest in May. Sucrose was the largest contributor proportionately to TNC daily means across accessions in May (0Æ33), August (0Æ30) and September (0Æ38). Glucose composed an equivalent proportion of TNC in the August harvest. Starch concentration was highest in May at 53 g kg ADW and lowest in August at 23 g kg ADW. The TNC concentration increased by 22Æ4 (May), 16Æ8 (July), 21Æ0 (August) and 30Æ8 g kg ADW (September) from dawn to dusk. Forage samples taken to estimate preference by ruminants or for TNC analyses should be cut and preserved within 1 h to control the diurnal variation of TNC proportionately within 0Æ05. Tall fescue should generally be cut between noon and sunset for TNC concentrations to be greater than the daily mean.