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

Author
item Lamb, Joann
item Jung, Hans Joachim
item Riday, Heathcliffe

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2012
Publication Date: 9/1/2012
Citation: Lamb, J.F., Jung, H.G., Riday, H. 2012. Harvest impacts on alfalfa stem neutral detergent fiber concentration and digestibility and cell wall concentration and composition. Crop Science. 52(5):2402-2412.

Interpretive Summary: The nutritive value of alfalfa stems can affect the amount of forage animals eat and the amount of energy the animals receive from the forage in dairy and beef production systems. Alfalfa stems with enhanced digestibility could increase profitability in these livestock production industries. In an alfalfa biomass or biofuel energy production system, stems are separated from leaves (sold separately as livestock feed) and processed to produce liquid fuel (ethanol). Therefore, increased concentrations of stem sugars (used to produce ethanol) are important plant traits for new alfalfa varieties developed for use in biofuel production systems. Several recent reports have suggested that it is difficult to improve alfalfa stem nutritive value and/or sugar concentration because these stem characteristics were highly affected by the growing conditions where the alfalfa hay is produced. A study was conducted to evaluate stem nutritive value and sugar concentration in several alfalfas planted at low and high plant population numbers at two locations and harvested at two maturity stages, early bud (four cuts per growing season) and late flower (three cuts per growing season) for 2 years for a total of 28 harvests. Plant population differences did not affect stem digestibility or stem sugar concentration. Stem digestibility was greater at the early flower stage while stem sugars were greater at the late flower stage of maturity. Stem digestibility and sugar concentrations varied a great deal at the 28 different harvests making it difficult to identify cultivar differences for these stem characteristics. Small but reliable cultivar differences were found for one of the stem sugars suggesting that selection for changes in the combination of stem sugars was possible. The large inconsistency in response for these stem traits across the 28 harvests suggested that in a plant breeding program with goals to improve stem digestibility and sugar concentration, alfalfa stems will need to be evaluated over several harvests to identify individual plants with consistent differences in stem nutritive value.

Technical Abstract: Alfalfa (Medicago sativa L.) stem fiber concentration and digestibility, lignin, and polysaccharide composition impact energy availability for livestock and biofuel conversion efficiency and are affected by maturity stage and environmental influences. We evaluated stem neutral detergent fiber (NDF) concentration, 16-h and 96-h in vitro neutral detergent fiber digestibility (IVNDFD), total cell wall (CW) concentration, Klason lignin (KL), cellulose (CEL), pectin (PEC), and hemicellulose (HC) as proportions of the cell wall in eight germplasms established at two plant densities at two locations and harvested at two maturity stages, early bud (four cuts per season) and late flower (three cuts per season) for 2 years for a total of 28 harvests. Growth environment at each individual harvest date and harvest maturity stage had the greatest impact, while plant density had no effect on stem quality traits. Stem NDF, CW, and CEL concentrations were greater at late flower, while 16-h and 96-h IVNDFD and PEC concentration were greater at early bud. Stem KL and HC were variable but comparable at the two maturity stages. Correlations summarized over the 28 harvests showed that as NDF or CW concentration increased, CEL increased, KL and HC remained relatively constant, and 16-h and 96-h IVNDFD and PEC decreased. Small but consistent entry differences were found for stem NDF concentration and PEC, suggesting that selection for changes in stem fiber concentration and cell wall composition were feasible. The large variability in response for stem quality traits across the 28 harvests suggested that in a program to modify stem fiber and cell wall composition, alfalfa stems will need to be screened over several harvests to identify individual plants with consistent differences in stem NDF, IVNDFD, CW, KL, CEL, and PEC.