At 14-day intervals one of 7 cohorts of Thurber needlegrass (Stipa thurberiana Piper) plants was defoliated to a 2.5-cm stubble to describe initial growth rates, determine defoliation effects on subsequent regrowth accumulations, relate regrowth potential to available soil moisture, and determine the nutritional value of initial growth and regrowth for livestock. Despite substantial differences in precipitation between 1985 and 1986 in southeast Oregon (77% and 111% of long term average), accumulation rates of Thurber needlegrass were approximately equal, and are strongly correlated with soil moisture. Maximum herbage production the second year consisted of 20% regrowth, and there was either no regrowth, or its rate declined (the second year) after the 19 June defoliation event. Crude protein content of the initial growth component declined with season progression and even fell below the recommended 7.5% level by early July 1985, and NDF (neutral detergent fiber) ranged between 40-70 % (increasing with plant maturity). However, in the regrowth component, crude protein was slightly higher after the April defoliation and much higher in the May and June defoliation events (no analysis was done in July) and NDF values ranged from 50 - 70%. Managers contemplating 2-crop grazing regimes for Thurber needlegrass should base scheduling on plant phenology, soil moisture considerations and historic use rather than specific calendar dates.
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