Harvest impacts on alfalfa stem neutral detergent fiber concentration and digestibility and cell wall concentration and composition

Alfalfa (Medicago sativa L.) stem fiber concentration and digestibility, lignin, and polysaccharide composition impact energy availability for livestock and biofuel conversion. We evaluated stem neutral detergent fiber (NDF) concentration, 16- and 96-h in vitro neutral detergent fiber digestibility (IVNDFD), total cell wall (CW) concentration, and proportions of Klason lignin (KL), cellulose (CEL), pectin (PEC), and hemicellulose (HC) in the cell wall for eight germplasms at two plant densities at two locations harvested at early bud (four cuts) and late flower (three cuts) for 2 yr. Growth environment influences at each harvest had the greatest impact on stem quality traits while plant density had no effect. Stem NDF, CW, and CEL were greater at late flower while 16- and 96-h IVNDFD and PEC were greater at early bud. Stem KL and HC were variable but comparable at the two maturity stages. Correlations indicated that as NDF or CW increased, CEL increased, KL remained relatively constant, and 16- and 96-h IVNDFD and PEC decreased. The large variability in response for stem quality traits suggested that to modify stem fiber and cell wall composition, alfalfa will need to be screened over several harvests to identify plants with consistent differences in stem quality.