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Temporal and Vertical Distribution of Nonstructural Carbohydrate, Fiber, Protein, and Digestibility Levels in Orchardgrass Swards

^a Dep. of Plants, Soils, and Biometeorology, Utah State Univ., 4820 Old Main Hill, Logan, UT 84322-4820
^b USDA-ARS Northwest Irrigation and Soils Research Lab., Kimberly, ID 83341
^c USDA-ARS Plant Sci. Research Unit, Dep. of Crop Sci. and Dep. of Animal Sci., Box 7620, North Carolina State Univ., Raleigh, NC 27695-7620

^* Corresponding author (tgriggs{at}ext.usu.edu)

Received for publication February 7, 2006. Herbage nonstructural carbohydrates (NC) contribute to livestock performance and silage fermentation. Knowledge of the distribution patterns of NC and other nutritional constituents in orchardgrass (Dactylis glomerata L.) swards could support harvest management decisions. Our objective was to determine diurnal and vertical patterns of total NC (TNC), crude protein (CP), and neutral detergent fiber (NDF) concentrations, and in vitro true dry matter digestibility (IVTDMD) and NDF digestibility (NDFD) in orchardgrass swards in October, June, and August. Herbage was sampled at 6-h intervals between 0100 and 1900 h from horizons positioned 40 to 27, 27 to 18, 18 to 12, and 12 to 8 cm above soil surface. Herbage composition varied among horizons in all months, and diurnally only in June and August. In June and August, only TNC with maxima of 109 to 123 g kg^–1 at 1900 h exhibited consistent diurnal patterns. Swards harvested to residual heights of 18, 12, or 8 cm exhibited little spatial variation in TNC during June and August, but CP, NDF, and IVTDMD varied with harvest depth on all dates. As swards were harvested to successively greater depths, TNC increased in October, but not in June and August. In contrast, CP and IVTDMD decreased, and NDF increased, for harvests to successively greater depths in all months. For harvests in June and August, manipulation of depth would capture more variation in CP, NDF, and IVTDMD, but manipulation of time of day of harvest would capture more variation in TNC to meet animal performance and silage fermentation requirements.

Abbreviations: CP, crude protein • DM, dry matter • IVTDMD, in vitro true dry matter digestibility • NC, nonstructural carbohydrate • NDF, neutral detergent fiber • NDFD, neutral detergent fiber digestibility • NIRS, near-infrared reflectance spectroscopy • TNC, total nonstructural carbohydrates • WSC, water soluble carbohydrates