When managed as pasture, the CP concentration in tall fescue generally was similar to or less than that of similarly managed orchardgrass, Kentucky bluegrass, or reed canarygrass (Phalaris arundinacea L.) (Item A, Table 11-2). In most cases CP concentrations were adequate to support acceptable animal daily performance (National Research Council, 1996). The noted exceptions were in the summer and autumn, when CP concentrations can drop below 100 g/kg.
The inclusion of tall fescue, Kentucky bluegrass, or orchardgrass in a mixture with alfalfa (Medicago sativa L.) (Item A, Table 11-2) resulted in all three grasses having low CP, averaging 91, 107, and 107 g/kg, respectively. The use of irrigation on tall fescue generally depressed CP concentration regardless of cultivar (Item B, Table 11-2).
Nitrogen application increased the CP concentration whether forage was harvested in the vegetative, boot, or headed stages of maturity-a trend that carried over to the summer regrowth (Item C, Table 11-2). Crude protein concentrations in the spring generally were greater than those in the summer.
Defoliation intensity altered CP, with greatest concentrations occurring from regimes with more frequent cuttings (Item D, Table 11-2). Crude protein concentrations decreased during summer, but could be increased by raising the stubble height. Although not shown in Table 11-2, CP concentration of tall fescue harvested to an 11- to 9-cm stubble declined to 133 g/kg in late May (spring) of Year 1 and 135 g/kg in July of Year 2, but in Year 3 concentrations remained above the August low CP concentration of 155 g/kg. The respective number of cuts per year totaled 14, 15, and 22 (Burns et al., 2002). These year-to-year differences, associated mainly with rainfall and temperature, can greatly influence tall fescue composition during stress periods in summer.
Dry Matter Disappearance and Fiber Fractions
The DMD of tall fescue was, with few exceptions, greater than that obtained from orchardgrass in both summer and autumn (Item A, Table 11-3). This difference was reflected also in reduced NDF and ADF concentrations. Although season altered DMD, with summer disappearance the least, little difference was noted among tall fescue cultivars (Item B, Table 11-3). This was observed also for NDF and ADF where data were available. Regardless of stage of maturity and subsequent regrowth, N fertilization generally increased DMD and decreased NDF and ADF concentrations (Item C, Table 11-3). In the winter season, forage cut to a 5-cm stubble generally had greater DMD in the green tissue, and DMD increased at higher N rates. This is in contrast to forage cut at 10 cm where the green tissue was similar in DMD among N rates.
Defoliation intensity showed little effect in the spring when forage cut from a 10-cm canopy height to a 5-cm stubble (10-5) was compared with forage cut from 15 cm to a 5-cm stubble (15-5) or from 11 cm to a 9-cm stubble (Item D, Table 11-3). In summer, however, cutting 15-5 decreased DMD when compared to 10-5. In contrast, raising the stubble to 9 cm increased DMD. This is consistent with the increase in DMD normally found higher in the plant canopy. Raising the stubble from 5 to 9 cm also reduced NDF and ADF, indicating that raising the grazing height during the summer stress period would increase utilization of forage with greater nutritive value.
The diurnal change in soluble carbohydrate concentrations shows that tall fescue reached higher concentrations of soluble carbohydrates between 0600 h and 1800 h than either Kentucky bluegrass or bromegrass (Item A, Table 11-3), although similar trends occurred for all three forages. Greater soluble carbohydrate concentrations in afternoon-harvested than in morning-harvested forages improved nutritive value (Holt and Hilst, 1969; Lechtenburg et al., 1972; Burns et al., 2001).