EFFECT OF DEFOLIATION INTENSITY ON REGROWTH OF TALLGRASS PRAIRIE

Grazing trials were conducted in north and south-central Oklahoma thro ughout the growing season of 1989 and 1990 in an attempt to explain li ve herbage accumulation rate of tallgrass prairie as a function of liv e residual herbage level. A 1-2 day grazing period on 8 treatment padd ocks began 26 May (Trial 1), 7 July (Trial 2), and 18 August (Trial 3) of each year. Two replicate paddocks per trial were subjected to stoc king densities of 7,600, 15,200, 22,700, and 30,300 kg animal weight h a-1. Live herbage was measured immediately after grazing to determine live residual herbage level and 2,4,6, and 8 weeks after grazing to de termine live herbage accumulation. Live herbage accumulation rate was determined as the first derivative with respect to day after grazing d ay of polynomial regression equations fit to live herbage accumulation data. Maximum live herbage accumulation rate decreased as season prog ressed but the time required to reach maximum live herbage accumulatio n rate was not dependent upon season. Live residual herbage level was a significant parameter in equations describing live herbage accumulat ion rate in 6 of 9 trials.