Trade-Offs in Growth, Persistence, and Quality of Summer-Active and Summer-Dormant Tall Fescues.

Tall fescue (Lolium arundinaceum) populations with genetic origins in continental Europe (e.g. 'Kentucky-31') are considered summer active because they respond to summer rains by resuming growth. Populations originating in the Mediterranean region possess varying degrees of summer dormancy, meaning that summer growth is reduced relative to summer-active types, even when well watered. Summer-dormant types survive prolonged summer droughts better than summer-active types. Trade-offs associated with the summer-dormant relative to summer-active types include greater autumn and winter growth, lower annual forage yield, greater risk of winter injury, and earlier decline in forage quality in spring owing to earlier flowering. These themes will be illustrated with data from field trials conducted simultaneously in northwest Arkansas and north-central Texas. We also propose a numerical index for quantifying the degree of summer dormancy expression as a ratio of summer dry matter (DM) yield to autumn DM yield.