Minimal Irrigation Requirements of Kentucky Bluegrass and Tall Fescue Blends in the Northern Transition Zone

Lawns in the cool-humid region typically consist of mixtures or blends of cool-season turfgrass species and cultivars. To maintain a desirable aesthetic appearance and maximize seasonal greenness, many lawns receive supplemental irrigation. Turfgrass breeders have developed superior cultivars with reduced water needs, but the exact proportion of these grasses to include in lawn seed blends to reduce irrigation needs has not been well documented. A field study was conducted to determine the irrigation requirements of various blend ratios (0, 25, 50, 75, and 100%, w/w) of drought-tolerant (DT) and drought-susceptible (DS) Kentucky bluegrass (Poa pratensis L., KBG) and turf-type tall fescue [Schedonorus arundinaceus (Schreb.) Durmort., syn. Festuca arundinacea Schreb.; TF] cultivars at two mowing heights (5.1 or 8.9 cm). Supplemental irrigation requirements were determined over a 74-d deficit irrigation period using a 70% green coverage threshold (GCT(70)) approach, where 12.7 mm of supplemental irrigation was applied if an individual plot fell below GCT(70) using digital image analysis. Total irrigation needs ranged from 66.7 to 176.9 mm, and TF generally required the least irrigation. For KBG, a blend containing >= 75% DT cultivar required the longest time to reach GCT(70) (25-33 d), the least irrigation (94-110 mm), and provided the highest overall visual quality. The TF responses were more variable, and the magnitude of differences among cultivar blends was less compared with KBG. These results indicate that where blending of cultivars is desired, the inclusion of cultivars with demonstrated drought tolerance in blends is important for reducing lawn irrigation needs.