|Griggs, Thomas - UTAH STATE UNIVERSITY|
|Macadam, Jennifer - UTAH STATE UNIVERSITY|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2006
Publication Date: May 11, 2007
Citation: Griggs, T.C., Macadam, J.W., Mayland, H.F., Burns, J.C. 2007. Temporal and vertical distribution of soluble carbohydrate, fiber, protein, and digestibility levels in orchardgrass swards. Agronomy Journal. 99:755-763. Interpretive Summary: Knowing the distribution of orchardgrass (Dactylis glomerata L.) sward constituents could improve harvest management. We determined daily levels of total nonstructural carbohydrates (TNC), crude protein (CP), fiber (NDF), and digestibilities of dry matter (IVTDMD) and fiber (NDFD) in sward horizons in October, June, and August. Constituent levels varied diurnally in summer only, but June and August patterns were inconsistent. At increasing harvest depths, levels of CP and IVTDMD decreased and NDF levels increased in all months, while TNC levels increased in fall but not in summer. Quality of harvested orchardgrass can be regulated by harvest timing and depth.
Technical Abstract: Herbage soluble carbohydrates (SC) contribute to livestock performance and silage fermentation. Knowledge of the distribution of SC and other constituents in orchardgrass (Dactylis glomerata L.) swards could support harvest management decisions. Our objective was to determine daily and seasonal levels of total nonstructural carbohydrates (TNC), crude protein (CP), neutral detergent fiber (NDF), in vitro true dry matter digestibility (IVTDMD), and NDF digestibility (NDFD) in orchardgrass sward horizons. Herbage was sampled at 6-h intervals in October, June, and August from horizons centered 10, 15, 22, and 34 cm above soil surface. Constituent levels varied diurnally in summer, but not in fall. Only TNC levels, reaching 109 to 200 g/kg at 1900 h in each period, had consistent diurnal patterns during June and August. There was little variation among TNC levels from harvests to residual heights of 18 to 8 cm during summer, but vertical gradients in CP, NDF, and IVTDMD levels were strong for harvest depths in all periods. Vertical gradients of TNC were reversed in October relative to summer, with higher TNC levels at greater depths of harvest in fall. In contrast, CP and IVTDMD decreased, and NDF increased, consistently with depth of harvest in all periods. Digestibilities of dry matter and NDF were closely associated, but neither was closely associated with TNC levels except in August. Diurnal patterns were more consistent among periods for TNC than for other constituents.