Changes in Forage Nutritive Value among Vertical Strata of a Cool-Season Grass Canopy

An understanding of the vertical distribution of nutritive value in cool-season grasses could support decisions regarding the management of residual mass and plant height to meet nutritional value targets. The objective of this study was to characterize the vertical distribution of nutritive value within a grass sward and to relate it to the morphological components of the herbage (lamina, stem + sheath, and dead matter). The research was conducted from April to October 2009 and 2010 in a mixed cool-season grass sward consisting primarily of tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons., formerly Festuca arundinacea Schreb.]. Growing periods were initiated in April, May, June, July, and August, during which forage was allowed to accumulate for the remainder of the growing season, with weekly sampling for nutritive value and morphological composition. Neutral detergent fiber (NDF) was significantly greater in the 5- to 15-cm strata than in the 15- to 25-cm in 32% of all initiation date x days after cutting combinations across years. The NDF concentration increased as the season progressed, which was associated with increasing dead matter and declining lamina content in the canopy. Differences in NDF digestibility among strata were less consistent than for NDF. For the May through August initiation dates, few nutritive value differences were found among strata, which were attributed to lower nutritive value in the 10-cm strata immediately above the stubble height. Consequently, we anticipate a small decrease in nutritive value of the diet of a grazing animal as it consumes tall fescue-dominant pasture.