Leaf damage in cool-season grasses subjected to simulated hoof pressures

Authors: Bartholomew, Paul; Williams, Robert

Submitted to: Forage and Grazinglands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2012
Publication Date: 4/20/2012
Citation: Bartholomew, P.W., Williams, R.D. 2012. Leaf damage in cool-season grasses subjected to simulated hoof pressures. Forage and Grazinglands. Available: http://www.plantmanagementnetwork.org/fg/.

Interpretive Summary: There is some evidence that hoof action of grazing animals may cause direct damage to pasture plants, but the extent and impact of such damage on pasture production or survival has not been well quantified. Recent studies have shown that point pressures exerted by hooves may exceed several-fold the average static pressures usually assumed in trampling studies, and this may mean that direct damage to plants is a greater problem in grazed pastures than is realized. In the study reported here we tested an electrolyte (cell omtent) leakage method and a fluorescence method of estimation of leaf damage arising from applied pressures of up to 290 psi, within the reported range of point pressures exerted by grazing livestock. We compared the susceptibility to damage of four common cool-season grasses (Orchardgrass, Smooth bromegrass, Tall fescue and Italian ryegrass) and of four varieties of Tall fescue. The fluorescence method was not an effective method of estimation of tissue damage. The electrolyte leakage method showed measurable increase in the extent of leaf damage with greater applied pressure and with shear force intended to simulate the action of a hoof on the surface of a pasture. Italian ryegrass was the most susceptible to damage among the species tested, and orchardgrass and smooth bromegrass were the least damaged. There were discernible differences in extent of tissue damage among the varieties of tall fescue tested. Estimation of tissue damage by measurement of electrolyte leakage from pressed leaf sections provides a rapid and low-cost method of comparing relative susceptibility to trampling damage of different species and varieties of pasture plants. Further work is needed to determine the effects of varying levels of tissue damage on plant growth and survival.

Technical Abstract: Although a potential for damage to tissue of grasses by grazing animals may exist, there are few reported estimates of susceptibility of different species or cultivars to trampling, and there is no standard method of measurement of damage to tissues of herbage. Experiments were undertaken with excised sections of leaf material of tall fescue (TF), smooth brome (SB), orchardgrass (OG) and Italian ryegrass (IRG) to evaluate damage caused by applied pressures, ranging in 400 kPa increments from 0 to 2000 kPa, and the incremental effect of shearing of tissue 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 72h after treatment. Electrolyte leakage showed significant increases with increased applied pressure, and differences among species or among TF cultivars were apparent. IRG was the most, and SB and OG the least, susceptible to pressure damage among the species tested. There was no consistent change in photosynthetic efficiency according to pressure treatments. The experiments showed that significant leaf tissue damage could occur as a result of application of point pressures within the range of hoof impact pressures reported in literature. Electrolyte leakage measures offer a means of measuring susceptibility of forages to trampling forces.