Author
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Sims, Phillip |
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Gillen, Robert |
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Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/7/1999 Publication Date: N/A Citation: N/A Interpretive Summary: A long-term study was conducted at the Southern Plains Experimental Range to determine the carrying capacity of the southern plains mixed-grass prairie. Vegetation responses and yearling steer gains on two replicates of three different grazing intensities were measured between 1941 to 1951. The light, moderate, and heavy grazing treatments, set at 16, 21, and 33 animal unit days per acre, were grazed with straight-bred Hereford steers from 13 November to 29 September. Basal cover of the individual herbaceous species and canopy cover of the shrubs were measured along 1289, approximately 33 ft line-transects in the six pastures (about 215 per pasture). All treatments showed significant recovery from a long history of severe grazing and the drought of the 1930's. Vegetation improvement was largely attributed to the favorable precipitation during the study. The basal cover of all perennial grasses was about 5 percent in 1941 and increased to between 8.6 and 14.8% by 1951. The increases were greater in the heavily stocked pastures compared to the light and moderate grazing intensity treatments. Steer gains averaged 370 lb per head. Of this total, 295 lb or 80% occurred in the summer period (April-September). Total live weight gain per head decreased as stocking rate increased. Stocking rate affected gain per head in both the winter and summer grazing periods. Live weight gain per acre increased as stocking rate increased. Maximum gain per acre was not reached within the bounds of the experimental treatments. Net return per acre increased as stocking rate increased. Based on this initial study, carrying capacity of this prairie was at least 21 and perhaps as much as 33 AUD per acre. Technical Abstract: This investigation was to determine the carrying capacity of the southern plains mixed-grass prairie by measuring vegetation and yearling steer gain responses to two replicates of three different grazing intensities between 1941 to 1951. The light, moderate, and heavy grazing treatments, set at 41, 53, and 82 animal unit days per ha (AUD ha-1), were grazed with straight-bred Hereford steers from 13 November to 29 September. Basal cover of the individual herbaceous species and the canopy cover of the shrubs were measured along 1289, 10 m line-transects in the six pastures (about 215 per pasture). All treatments showed significant recovery from a long history of severe grazing and the drought of the 1930's. Vegetation improvement was largely attributed to the favorable precipitation during the study. The basal cover of all perennial grasses was about 5 percent in 1941 and increased to between 8.6 and 14.8% by 1951. The increases were egreater in the heavily stocked pastures compared to the light and moderate grazing intensity treatments. Steer gains averaged 168 kg per head. Of this total, 134 kg or 80% occurred in the summer period (April-September). Total live weight gain per head decreased as stocking rate increased. Stocking rate affected gain per head in both the winter and summer grazing periods. Live weight gain per acre increased as stocking rate increased. Maximum gain per hectare was not reached within the bounds of the experimental treatments. Net return per hectare increased as stocking rate increased. Based on this initial study, carrying capacity of this prairie was at least 53 and perhaps as much as 82 AUD ha-1. Interpretative Summary |
