Intrinsic shear strength of leaves of pasture grasses and legumes

Abstract

The intrinsic shear strength of leaves of pasture grasses and legumes was compared. Intrinsic shear strength is calculated as the force required to shear a leaf, divided by the length of the cutting blade in contact with the leaf material. Intrinsic shear strength was similar along a leaf blade of Festuca arundinacea, but differed significantly for different leaves on a plant. Different leaves on a plant of Phalaris aquatica also differed significantly in intrinsic shear strength. Leaves that had recently reached full expansion had a higher intrinsic shear 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 of the plants and, in particular, by the climatic conditions under which the leaves developed. The intrinsic shear strength of grass leaves was 38–68 times that of legumes leaves, with a 1 · 8-fold difference between the species of grasses examined. Significant variation in intrinsic shear strength exists between both species of grasses and between species of grasses and legumes, indicating that there is significant scope for the genetic improvement of pasture grasses. However, it is unlikely that grasses could be improved to achieve the performance levels of legumes.