Diurnal Variation in Alfalfa (Medicago sativa L.) Dry Matter Yield and Overnight Losses in Harvested Alfalfa Forage1

Abstract

AbstractResearch reported here was designed (a) to study diurnal variation in dry matter yield and nonstructural carbohydrate percentages in alfalfa (Medicago sativa L.) and (b) to compare overnight dry matter and carbohydrate changes in alfalfa cut and left in the field with the changes in standing alfalfa.First‐ and second‐growth alfalfa were harvested at 7 AM and 7 PM over three 3‐day periods. Each evening, additional alfalfa samples were cut and left overnight in the field so that overnight dry matter and carbohydrate changes in cut and uncut alfalfa could be compared.Dry matter yields were measured, and freeze‐dried, ground samples were analyzed for carbohydrates. Sucrose and reducing sugars were extracted with ethanol. Starch in the remaining residue was hydrolyzed with amyloglucosidase. The carbohydrates in the extracts were quantitatively assayed using ferricyanide, resorcinol, and phenol‐sulfuric acid procedures.Dry matter yields, as well as starch and sucrose concentrations, were significantly higher in the evening than the following morning. Glucose and fructose percentages did not change from evening to morning. Through the day, dry matter increased by 5 to 12%, but half or more of this increase disappeared during the night. Standing alfalfa lost 5.5% of its dry matter overnight, while cut forage lost 7.2% overnight in May and 11.0% in July. Dry matter losses in the cut forage were closely related to night temperature, with greatest losses occurring on warmest nights. Cut forage, however, retained higher starch, sucrose, and fructose concentrations through the night than the standing crop. Seventy percent of the night loss of dry matter in standing alfalfa was nonstructural carbohydrate, but only 20% of the loss in cut material was carbohydrate.