EFFECT OF STAGE OF MATURITY AND GROWTH-CYCLE ON SHEARING FORCE AND CELL-WALL CHEMICAL-CONSTITUENTS OF ALFALFA STEMS

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 w ere measured at several segments on the stem. In exp. 1, Anchor, Barri er and Vernal alfalfa, at the second and third regrowth were harvested at the early bud stage. Stem weight and diameter were larger at the s econd regrowth for all stem segments. A numeric trend for lower stem d iameter 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 c ultivars and ADL was highest at the second regrowth (P < 0.01). In exp . 2, Anchor, Barrier and Vemal alfalfa, in the second production year, were harvested at four stages of maturity, early bud, early flower, l ate flower and early seed pod. A significant stage of maturity x stem segment effect was observed for shearing force, diameter, and weight. Shearing force, stem diameter and weight measurements generally increa sed as the plants aged for all stem segments. Quadratic relationships (P < 0.0001) for shearing force, stem diameter and weight were observe d with increasing stage of maturity for all stem segments. Generally, hemicellulose and lignin contents increased as the plants matured, whi le cellulose concentrations were variable. Both stage of maturity and growth cycle affected shearing force of alfalfa stems and this was ass ociated with changes in stem diameter, weight and its cell wall chemic al constituents.