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Alfalfa (Medicago sativa L.) cut in the late afternoon has a greater nonstructural carbohydrate (NSC) concentration than AM-cut alfalfa but this difference might not be maintained during wilting. We monitored NSC concentration of PM- and AM-cut alfalfa during wilting in narrow and wide swaths. Field-grown alfalfa was cut either at 1800 h (PM) on days without rain (Day 0) or at 0800 h (AM) the following morning (Day 1) in seven growth cycles over 3 yr. Samples taken during wilting were analyzed for NSC (soluble carbohydrates + starch). At cutting, PM-cut alfalfa had consistently greater NSC concentration [+6 to 54 g kg-1 of dry matter (DM)] than AM-cut alfalfa. The NSC concentration decreased during wilting at rates that depended on growth cycles (0.2-3.5 g kg-1 DM h-1 on Day 1) but this decline was similar for AM- and PM-cut alfalfa. When cut alfalfa reached 350 g DM kg-1 fresh matter (FM) on Day 1, NSC concentration was greater for PM- than for AM-cut alfalfa (average of 15 with a range of 4-37 g kg-1 DM) and greater for the wide than narrow swaths (average of 7 with a range of 1-11 g kg-1 DM). Photosynthesis continued for 3 h on the morning ofAM cutting for both PM- and AM-cut alfalfa until DM concentration reached approximately 350 g DM kg-1 FM. The combination of late PM-cutting and wilting in wide swaths can be used to increase the NSC concentration of wilted alfalfa. [ABSTRACT FROM AUTHOR]

Increasing the nonstructural carbohydrate (NSC) concentration of forages improves N use efficiency by dairy cows. We studied the diurnal variations of NSC concentration and other nutritive value attributes in alfalfa (Medicago sativa L.) to determine the best time during the day to cut alfalfa for maximizing NSC concentration. Field-grown alfalfa was cut every 2 h between 0600 and 2000 h on six different days around the early flower stage of development during spring growth and summer regrowth at two sites in eastern Canada. Concentrations of NSC [soluble carbohydrates (SC) plus starch], neutral detergent fiber (NDF), acid detergent fiber (ADF), and N, along with in vitro true digestibility (IVTD) of dry matter (DM) and in vitro digestibility of NDF were determined. The NSC concentration increased during the day in all growth cycles and sites due mostly to an increase in starch concentration. The diurnal increase of NSC concentration, however, varied with growth cycles and sites from 15.5 to 41.9 g kg-1 DM, and it was accompanied by a decrease of 1 to 2 g kg-1 DM in N concentration. At the site where the increase in alfalfa NSC concentration was greater than 30 g kg-1 DM, concentrations of ADF and NDF also decreased by 9 to 27 g kg-1 DM while IVTD increased by 3 to 16 g kg-1 DM. Greatest NSC concentrations were reached between 11 and 13 h after sunrise and the best time during the day to cut alfalfa for maximizing NSC concentration in eastern Canada is between 1600 and 1800 h. [ABSTRACT FROM AUTHOR]