Competitive Ability of Tall Fescue against Alfalfa as a Function of Summer Dormancy, Endophyte Infection, and Soil Moisture Availability

Management practices of summer-dormant cool-season grasses, including compatible legume species, are not well understood. In a greenhouse experiment, competitive ability of two summer-dormant (Flecha and TX06V) and a summer-active (PDF) tall fescue [Schedonorus arundinaceus (Schreb.) Dumort = Lolium arundinaceum (Schreb.) Darbysh.] was evaluated in associations with alfalfa (Medicago sativa L.) cv. Bulldog 505. Fescue cultivars were either infected with Neotyphodium coenophialum (Morgan-Jones & Gams.) Glenn, Bacon, & Hanlin comb. nov. fungal endophyte or noninfected. Monocultures and binary mixtures were exposed to a gradually imposed soil moisture deficit stress (30% soil water capacity [SWC]) from June through August or maintained at 90% SWC (control). Indices of competitive interactions (relative yield [RY], relative yield total [RYT], and aggressivity [AGR]) were calculated. The RY of summer-dormant tall fescue was less, whereas RY of summer-active tall fescue was similar to that of alfalfa. The RYT values for alfalfa-tall fescue mixtures were not different from 1 under nonlimited soil moisture, but alfalfa-Flecha mixture had RYT <1 under soil moisture deficit. The AGR of summer-dormant tall fescue was lower, but AGR of summer-active tall fescue was similar to that of alfalfa. Results suggest that summer-active tall fescue effectively competes with alfalfa, but summer-dormant tall fescue cultivars have lower competitive ability than alfalfa. In addition, endophyte infection increased competitive ability of TX06V and PDF but not of Flecha.