Rangeland and steer responses to grazing in the Southern Plains

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 2 replicates of 3 different grazing intensity treatments between 1941 and 1951. The light, moderate, and heavy grazing treatments, set at 41, 53, and 82 animal-unit-days ha-1 (AUD ha-1), were grazed with straight-bred Hereford steers with an initial weight of 213 +/- 11 (SD) kg from about 13 November to 29 September each year. Basal cover of the individual herbaceous species and the canopy cover of the shrubs were measured along 1,289, 10-m line-transects in the 6 pastures (about 215 per pasture). All treatments showed recovery from a long history of severe grazing and the drought of the 1930's. Vegetation change was largely attributed to favorable precipitation during the study. The basal cover of all perennial grasses was about 5% in 1941 and increased to between 8 and 15% by 1951. The increases were greater in the heavily stocked pastures compared with 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 (Apri1-September). Total live weight gain head-1 decreased as stocking rate increased. Stocking rate affected gain head-1 in both the winter and summer grazing periods. Live weight gain hectare-1 increased as stocking rate increased. Apparently, the maximum gain hectare-1 was not reached within the bounds of the experimental treatments. Net return hectare-1 increased as stocking rate increased. Based on this initial study, carrying capacity of this prairie was greater than 53 AUD ha-1. During extended periods of good rainfall, the carrying capacity of Southern Plains mixed-prairie may reach 82 AUD ha-1.