Silage Fermentation of PM‐ and AM‐Cut Alfalfa Wilted in Wide and Narrow Swaths

Abstract

ABSTRACTNonstructural carbohydrate (NSC) concentration in alfalfa (Medicago sativa L.) increases by cutting in the afternoon (PM) and wilting in wide swaths but the impact of this greater concentration during silage fermentation is not well known. We determined if increased NSC concentration associated with PM‐cutting and wide swathing is maintained during fermentation and whether it affects conservation attributes of wilted alfalfa silages. The cutting time effect was measured in spring growth and summer regrowth of 2007 and 2008 (Experiment 1) while the combined effect of cutting time and swathing type was measured in spring growth and summer regrowth of 2008 (Experiment 2). Alfalfa was field wilted [≈390 g dry matter (DM) kg−1 fresh matter] and ensiled in mini‐silos. Differences in alfalfa NSC concentration at ensiling (10 to 36 g kg−1 DM) due to PM‐cutting combined or not with wide swaths were reduced during silage fermentation to between 0 and 15 g kg−1 DM mostly through a reduction in soluble carbohydrate concentration. When NSC concentration differences at ensiling were > 10 g kg−1 DM, silage conservation attributes were improved with lower pH (−0.2 to −0.4), greater concentrations of lactate (+8 to +20 g kg−1 DM), and lower concentrations of volatile fatty acids (−8 to −11 g kg−1 DM) and NH3–N (−6 to −11 g kg−1 total N). Improved silage conservation attributes along with a greater residual starch concentration from NSC‐enriched alfalfa has the potential to improve milk production.