A SHEARING TECHNIQUE MEASURING RESISTANCE PROPERTIES OF PLANT STEMS

A shearing technique was developed to measure fracturing properties of plant stems. Shearing force measurements assess the amount of energy required to fragment plant tissue as an indication of resistance to pa rticle breakdown during mastication. The objective of this study was t o develop a rapid and inexpensive method of accurately measuring the s hearing properties of forage stems. Shearing properties of alfalfa ste ms were measured by shearing 20 main stems from each of 24 cultivars. Stems were dried and divided into three 16 cm segments, top, middle an d bottom. Each segment was sheared between two nodes at the approximat e mid-point using an Ottawa Texture Measurement System with a Warner-B ratzler blade (dull grade) lowered at 1.35 mm s(-1). Instrument repeat ability was determined using a homogenous material (plastic coffee sti rrers) with mechanical and textural properties similar to those of a p lant stem. The shearing technique provided a repeatable and rapid meas urement of shearing force (coefficient of variation for plastic stirre rs, 4.2%). For alfalfa stems harvested at similar physiological maturi ty, shearing forces for each shearing location on Be stem differed (P < 0.001) among cultivars. At all shearing locations, shearing force va ried considerably between cultivars; however, variations among shearin g locations were similar. Shearing force was significantly correlated with diameter, weight, linear density and, to a lesser extent, with th e cell wall chemical constituents of the stem.