Effect of stage of maturity and growth cycle on shearing force and cell wall chemical constituents of alfalfa stems

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Abstract
Two experiments were conducted to assess whether stage of maturity and growth cycle affected shearing force of alfalfa (Medicago sativa L.) stems. In both experiments, stem shearing force, diameter and weight were measured at several segments on the stem. In exp. 1, Anchor, Barrier and Vernal alfalfa, at the second and third regrowth were harvested at the early bud stage. Stem weight and diameter were larger at the second regrowth for all stem segments. A numeric trend for lower stem diameter in Vernal compared to Anchor and Barrier was observed. For all stem segments, shearing forces for Anchor and Barrier were lower than for Vernal and shearing force was highest for second regrowth. Vernal had higher NDF, ADF, hemicellulose and cellulose content than other cultivars and ADL was highest at the second regrowth (P < 0.01). In exp. 2, Anchor, Barrier and Vernal alfalfa, in the second production year, were harvested at four stages of maturity, early bud, early flower, late flower and early seed pod. A significant stage of maturity × stem segment effect was observed for shearing force, diameter, and weight. Shearing force, stem diameter and weight measurements generally increased as the plants aged for all stem segments. Quadratic relationships (P < 0.0001) for shearing force stem diameter and weight were observed with increasing stage of maturity for all stem segments. Generally, hemicellulose and lignin contents increased as the plants matured, while cellulose concentrations were variable. Both stage of maturity and growth cycle affected shearing force of alfalfa stems and this was associated with changes in stem diameter, weight and its cell wall chemical constituents. Key words: Alfalfa, stage of maturity, growth cycle, shearing force, cell wall chemical constituents

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