Evaluation location: Oklahoma, United States
The field was located on The Noble Foundation Headquarters Farm in Ardmore, OK (34 10 N, 97 04 W); soil type was a Konsil loamy fine sand (fine-loamy, siliceous, thermic Ultic Paleustalfs). Plots were grazed by beef cattle (Bos taurus), at a stocking rate of approximately 4052 kg live weight hectare -1, from 9 April to 23 April, and 29 May to 5 June, 1998. In this and all subsequent trials, plots were grazed to maintain a stubble height of approximately 5 cm or less, except as noted, and very little or no summer re-growth occurred following grazing because of onset of summer dormancy. In November, 1998, plants were assigned a vigor rating, with 0 being dead, 9 being maximum vigor. Vigor ratings were based on visual estimates of the amount of fall growth, density of tillering, and plant diameter, or for rhizomatous species, plant spread. As for all trials, fall re-growth had essentially ceased when vigor ratings were taken.Two heifers (216 kg live weight hectare -1) grazed the approximately 2.35 hectare field from December, 1998 to 23 March, 1999, after which time they were confined to the approximately 0.4 hectare tall fescue planting, resulting in an estimated stocking rate of 1350 kg live weight hectare -1. Heifers were removed on 14 June, 1999; one heifer grazed the area (730 kg live weight hectare -1) from 23 June - 13 July. Vigor ratings for the tall fescue planting were taken in November, 1999 following the same procedures as for 1998.