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Publication Date
1981
Description
Summary Utilization of a monotypic stand of perennial grass by cattle is generally assumed to be a random process that can be adequately measured by counting the number of plants grazed or by comparing biomass on caged and grazed plots. At a similar level of approximation, grazing is often simulated experimentally by clipping down to a prescribed height. The purpose of our study was to examine defoliation in more detail, following grazing severity and frequency on an individual plant basis with an interval of only 48 hours between observations. The study was conducted on two 28-ha pastures of crested wheatgrass (Agropyron cristatum [L.] Gaertn.), originally seeded 25 years earlier, in a semiarid area (320 mm annual precipitation) located in west central Utah, 8 km southwest of Eureka. Nearly 300 permanent plots (0.5 m2) were involved in the project. During 6 weeks of grazing by cattle injune and early July, 1979, the overall utilization was 46% by volume, with nearly 70% of all plants being grazed at least once. Only one-sixth of the grazed plants were defoliated on more than one occasion, and most of those were grazed just twice. Data analysis indicated a preference for moderate-sized plants, with less intensity of grazing on the smallest or largest size classes. Sixty percent of the smallest size-class plants were not grazed at all. For those plants that did experience defoliation, severity of grazing was inversely related to plant size. Grazing on these crested wheatgrass pastures was neither random nor uniform. The cattle removed forage in a fashion that varied according to plant size. Very small plants were grazed in a manner similar to a clipping simulation. Plants greater than 200 cm2 in basal area experienced a loss of less than half the plant volume, affecting less than half the plant cover, at an average defoliation event. The preponderance of biomass remaining in the large wolf plants at the end of the grazing period would suggest that estimating utilization by departure from amount of forage protected in ungrazed cages could underestimate actual utilization on the population of plants providing most of the consumed forage.
Citation
Norton, B E. and Johnson, P S., "Pattern of Defoliation by Cattle Grazing Crested Wheatgrass Pastures" (1981). IGC Proceedings (1981-2023). 14.
(URL: https://uknowledge.uky.edu/igc/1981/section7/14)
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Pattern of Defoliation by Cattle Grazing Crested Wheatgrass Pastures
Summary Utilization of a monotypic stand of perennial grass by cattle is generally assumed to be a random process that can be adequately measured by counting the number of plants grazed or by comparing biomass on caged and grazed plots. At a similar level of approximation, grazing is often simulated experimentally by clipping down to a prescribed height. The purpose of our study was to examine defoliation in more detail, following grazing severity and frequency on an individual plant basis with an interval of only 48 hours between observations. The study was conducted on two 28-ha pastures of crested wheatgrass (Agropyron cristatum [L.] Gaertn.), originally seeded 25 years earlier, in a semiarid area (320 mm annual precipitation) located in west central Utah, 8 km southwest of Eureka. Nearly 300 permanent plots (0.5 m2) were involved in the project. During 6 weeks of grazing by cattle injune and early July, 1979, the overall utilization was 46% by volume, with nearly 70% of all plants being grazed at least once. Only one-sixth of the grazed plants were defoliated on more than one occasion, and most of those were grazed just twice. Data analysis indicated a preference for moderate-sized plants, with less intensity of grazing on the smallest or largest size classes. Sixty percent of the smallest size-class plants were not grazed at all. For those plants that did experience defoliation, severity of grazing was inversely related to plant size. Grazing on these crested wheatgrass pastures was neither random nor uniform. The cattle removed forage in a fashion that varied according to plant size. Very small plants were grazed in a manner similar to a clipping simulation. Plants greater than 200 cm2 in basal area experienced a loss of less than half the plant volume, affecting less than half the plant cover, at an average defoliation event. The preponderance of biomass remaining in the large wolf plants at the end of the grazing period would suggest that estimating utilization by departure from amount of forage protected in ungrazed cages could underestimate actual utilization on the population of plants providing most of the consumed forage.
