Cell Wall Composition of Alfalfa Stems at Similar Morphological Stages and Chronological Age During Spring Growth and Summer Regrowth

Summer regrowth of alfalfa (Medicago sativa L.) is often more mature and consequently lower in herbage quality than spring‐grown alfalfa of similar chronological age. Alfalfa herbage samples taken at comparable maturity stages have similar quality. Whether cell wall composition is the same, however, is not known. We compared the cellulose, hemicellulose (HC), and lignin (CWL) concentrations in cell walls (neutral detergent fiber) of alfalfa stems at similar chronological ages and maturity stages. Alfalfa was harvested every 10 d during the spring and summer growth periods of 1984 and 1985. Maturity of alfalfa at each harvest was classified on a phenological scale of 0 to 9, and a mean stage number was calculated. Summer‐grown stems of alfalfa were more mature and therefore had a greater concentration of cell walls that were more lignified than spring‐grown stems of the same chronological age. To compare the cell wall composition of alfalfa stems grown in different environments at specific morphological stages, concentrations of cell wall, cellulose, HC, and CWL were regressed on mean stage number. Stem cell wall concentrations [R2 = 0.88, root error mean square (REMS) = 43 g kg−1] and CWL (R2 = 0.71, REMS = 13 g kg−1) increased quadratically, whereas cellulose (r2 = 0.52, REMS = 21 g kg−1) decreased linearly with increasing maturity stage. Cell wall hemicellulose was not related to maturity stage. Stem cell wall concentration and CWL were closely related to alfalfa maturity and could be explained well with a maturity index, whereas cell wall cellulose and HC were not well related to maturity but may have been related to other factors not accounted for in the maturity index.