Shearing force of alfalfa stems: effects of cultivar and shearing site

A 3-yr study was conducted to investigate the effect of shearing position o n shearing force characteristics in alfalfa (Medicago sativa L.) stems and to evaluate the relationship between cell wall (CW) chemical constituents a nd stem shearing force. Stems from plots of 24 alfalfa cultivars were harve sted from the second, third and fourth production years. Each stem was divi ded into three 16-cm segments: top, middle and bottom, and the force requir ed to shear each segment was measured using a modified Ottawa Texture Measu ring System. Cultivar by stem segment interactions were significant (P < 0. 05) for stem diameter, weight and shearing force. The middle and bottom ste m segments were the best sampling site to detect cultivar differences for s hearing force. Stem diameter and weight were generally the variables most a ssociated with shearing force for all three stem segments. However, shearin g force characteristics for certain cultivars could not be entirely explain ed by stem diameter or weight and may be affected by CW chemical constituen ts and/or structural tissues. The ADL concentrations were not consistently correlated to shearing force at the top and bottom segments over the 3 yr. For the bottom stem segment a negative relationship (r = -0.42, P < 0.001) resulted between shearing force and hemicellulose, while a positive relatio nship (r = 0.40, P < 0.001) resulted between shearing force and cellulose.