Turfgrass Consumptive Use Values for the Phoenix Area

Consumptive use (CU) curves that provide average rates of turfgrass evapotranspiration (ET T ) are widely used by irrigation professionals for design and management of turfgrass irrigation systems. For approximately 35 years, the bermudagrass lawn CU curve developed by the United States Department of Agriculture (Erie et al., 1965; Erie et al., 1982) has served as the lone published CU curve for turfgrass in Arizona. While the USDA CU curve has proven useful to the turf industry, turf professionals do question whether ETT values obtained from the curve are relevant to turf sys- tems commonly used in Arizona today. The USDA curve was developed for the summer turf season using a low-maintenance common bermudagrass mowed to a height of 3.8 cm (1.5") every four weeks, and watered every two weeks using flood irrigation (Garrot and Mancino, 1994). A relevant turf system today consists of hybrid bermudagrass maintained at a height of ~ 2 cm (0.75") and watered at frequent intervals using sprinkler irrigation. The practice of overseeding with ryegrass in the fall to maintain green cover in winter is also common today. The USDA CU curve does not address the issue of overseeding and provides no in- formation on ETT for the period mid-October through mid-April.