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Nonstructural carbohydrate concentration during field wilting of PM- and AM-cut alfalfa

Morin, C., Tremblay, G.F., Bélanger, G., Bertrand, A., Castonguay, Y., Drapeau, R., Michaud, R., Berthiaume, R., Allard, G. (2012). Nonstructural carbohydrate concentration during field wilting of PM- and AM-cut alfalfa, 104(3), 649-660. http://dx.doi.org/10.2134/agronj2011.0365

Abstract

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 of AM 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. © 2012 by the American Society of Agronomy. 5585 Guilford Road, Madison, WI 53711. All rights reserved.

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