Leaf Damage in Cool-season Grasses Subjected to Simulated Hoof Pressures

Abstract

Although grazing animals may potentially damage grass tissues, few reported estimates of susceptibility of different species or cultivars to trampling exist, and no standard method of leaf tissue damage measurement has been established. Experiments were undertaken with excised sections of leaf material of tall fescue [Schedonorus phoenix (Scop.) Holub], smooth bromegrass (Bromus inermis Leyss), orchardgrass (Dactylis glomerata L.), and Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] to evaluate damage caused by applied pressures, ranging in 400 kPa increments from 0 to 2000 kPa, and the incremental effect of tissue shearing while under pressure. Tissue damage was evaluated by estimation of electrolyte leakage from pressed leaf sections or by using a fluorometer to measure change in photosynthetic efficiency up to 72 h after treatment. Electrolyte leakage showed significant increases with increased applied pressure, and differences among species or among tall fescue cultivars were apparent. Among species tested, Italian ryegrass was the most, and smooth bromegrass and orchardgrass the least, susceptible to pressure damage. Photosynthetic efficiency did not consistently change according to pressure treatments. The experiments showed that significant leaf tissue damage could occur as a result of applied point pressures within the range of hoof pressures reported. Electrolyte leakage offers a means of assessing the susceptibility of forages to damage by trampling.