Water deficit, heat tolerance, and persistence of summer-dormant grasses in the U.S. southern plains

Summer-dormant cool-season grasses are being used in the Southern Plains of the United States in place of traditional summer-active cultivars for high-quality winter forage. One reason for this is the ability of cultivars with summer dormancy traits to tolerate increasing annual temperature, decreasing precipitation, and repeated severe summer droughts. Research on adaptation of these grasses and mechanisms of summer dormancy has been conducted at Vernon, TX, since 2000. The experimental location is in a semiarid, subtropical climate with bimodal rainfall pattern with peaks in May and September, and prolonged summer drought. Adaptation and persistence studies involved summer-dormant and summer-active cultivars of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.], orchardgrass (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), and hardinggrass (Phalaris aquatica L.). Summer-active types of these grasses were not adapted to this environment and could not survive the first summer after planting. Summer-dormant types were fully adapted and persisted for at least 5 to 8 yr, depending on species. The most adapted were tall fescue, hardinggrass, and to some extent orchardgrass [subsp. hispanica (Roth) Nyman]. Detailed studies have also been conducted by the Samuel Roberts Noble Foundation at Ardmore, OK. Both research centers have breeding programs for summer-dormant grasses.