Submitted to: Alfalfa Improvement Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/11/1999
Publication Date: N/A
Interpretive Summary: Forage breeding and nutrition programs often result in sampling standing forage for estimation of total nonstructural carbohydrates and other fiber and protein constituents. Growing plants accumulate sugars during the day resulting in increased sugar concentrations. This leads to a dilution of other components like fibers that may also be criterion in breeding and nutrition programs. This study was conducted to see how rapidly carbohydrates accumulated and how rapidly they might affect the apparent concentration of other constituents as a result of dilution. Alfalfa sampled at three hour intervals in May and again in September, showed sinusoidal variation in concentration of total nonstructural carbohydrates. These values were relatively linear between 0900 and 2100 hours and increased by 0.29 percentage units per hour in May and 0.54 in September. Samples should be taken within one hour to control diurnal variation within 5%. Alternatives would be to use time of day as a covariate or block across treatments.
Technical Abstract: Photosynthesizing plants accumulate soluble sugars through out the day and metabolize these to other products at night. These diurnal changes significantly affect ruminant animal preferences, dry matter intake, and some laboratory measurements of forage quality. A study of diurnal cycling of total nonstructural carbohydrates (TNC) in alfalfa provided evidence of a linear increase in TNC during the day. Cutting or sampling green forage for TNC or other plant constituents or for assessment of animal responses, must be done within one hour time periods to provide comparative data among experimental treatments or data must be blocked across time.