Grazing intensity effects on weed populations in annual and perennial pasture systems
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Authors: K. N. Harker, V. S. Baron, D. S. Chanasyk, M. A. Naeth, and F. C. Stevenson
Date: 2000
Journal: Weed Science
Volume: 48
Number: 2
Pages: 231-238
Summary of Methods: The effects of various grazing intensities on weed populations were examined for both perennial and annual improved forage pastures at the Lacombe Research Center in Alberta. Perennial pastures were dominated by smooth brome or meadow brome and annual pastures were planted to winter triticale or a mixture of winter triticale and barley. Cultivation practices for the annual pastures stayed constant and were similar to accepted practices throughout the area. Pastures were grazed by yearling heifers to three intensity levels (overgrazing with soil surface exposed), medium (optimum forage productivity for the animals) and low (allowing the plants to reach head stage before grazing) within 24 hours. Weed species were identified and counted in one 2 x 2 m cell grid each spring and fall for the duration of the study. Available forage and residual forage were determined by clipping forage to a 2.5 cm height in a 25 x 100 cm plot before and after each paddock was grazed.
Article Summary / Main Points: Increased grazing pressure, these two weed species increased in density, while the other seeded tame species were not affected by the different grazing intensities. Increased grazing pasture caused shepherds-purse density to be greater in perennial pastures than annual pastures. Available and residual forages were reduced with increased grazing pressure. Increased grazing pressure resulted in greater density of dandelion in perennial pastures. Shepherds-purse was the dominant species in annual pastures where dandelion was the dominant species in perennial pastures. This is believed to be due to annual cultivation and herbicide application on annual pastures and lack of both management techniques in perennial pastures. Perennial pastures did not always favor weed infestations and existing weed populations only increased when grazing was excessive.
Vegetation Types: Tame Pastures
MLRA Ecoregions: Not Applicable
Agrovoc Control Words: Weeds Pastures Grazing
Article Review Type: refereed
Article Type: Experimental Research
Keywords: improved pasture, species diversity, grazing pressure, density, shepards purse, capsella bursa-pastoris, dandelion, taraxacum officinale
Annotation: During this three year study annual precipitation was greater than normal two of three years, with precipitation being near normal the third year. Results may be different in years of lower than normal precipitations or drought periods.
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