INTRINSIC SHEAR-STRENGTH OF LEAVES OF PASTURE GRASSES AND LEGUMES

The intrinsic shear strength of leaves of pasture grasses and legumes was compared. Intrinsic shear strength is calculated as the force requ ired to shear a leaf, divided by the length of the cutting blade in co ntact with the leaf material. Intrinsic shear strength was similar alo ng a leaf blade of Festuca arundinacea but differed significantly for different leaves on a plant. Different leaves on a plant of Phalaris a quatica also differed significantly in intrinsic shear strength. Leave s that had recently reached full expansion had a higher intrinsic shea r strength than leaves from lower on a tiller. The leaves of different cultivars of P. aquatica differed in their intrinsic shear strength. Their strength appeared to be influenced by the stage of development o f the plants and, in particular, by the climatic conditions under whic h the leaves developed. The intrinsic shear strength of grass leaves w as36-68 times that of legumes leaves, with a 1.8-fold difference betwe en the species of grasses examined. Significant variation in intrinsic shear strength exists between both species of grasses and between spe cies of grasses and legumes, indicating that there is significant scop e for the genetic improvement of pasture grasses. However, it is unlik ely that grasses could be improved to achieve the performance levels o f legumes.