Defoliation of Intermediate Wheatgrass Under Seasonal and Short-Duration Grazing

Abstract

Defoliation of intermediate wheatgrass (Agropyron intermedium by cattle was examined under seasonal and short-duration grazing. Tiller height, number of green leaves per tiller, phenological status, and defoliation frequency were measured on individually marked tillers during 2 grazing seasons. Defoliations at high and low stocking densities (5.2 and 2.6 animal-units/ha) were examined during the 1983 growing season. At equal stocking rates, standing crop decreased more rapidly under low stocking density. Mean tiller height and mean number of leaves per tiller decreased linearly over time in both treatments. In 1984, 14 heifers were moved through 3 rotations of an 8 subunit short-duration grazing system in 72 days. A larger fraction of tiller height and a higher number of green leaves per tiller were defoliated during rotation one than during rotation three. Animals grazed the greatest number of tillers during rotation one. Biting rate varied logarithmically with the mean number of green leaves per tiller. Time spent grazing was significantly and inversely related to the mean number of green leaves per tiller. This result suggests that animals were selectively grazing green leaves over coarse stem, and spent more time searching for them as their numbers decreased.