Irrigated fescue grass ET compared with calculated reference grass ET

摘要

Cool-season, short, and well-watered grass is the world-wide standard reference for crop evapotranspiration (ET) research and practice. Fescue grass (Festuca arundinacea Schreb.) was grown at Bushland, TX since 1995, and its water use measured witha monolithic, weighing lysimeter. The grass was mowed (to 0.11 m) and irrigated frequently and managed for vigorous growth. It was irrigated with a subsurface drip irrigation (SDI) system. Data were analyzed for the period I July 1995 through December 1999 that included a wide diversity in climatic regimes. Several grass reference ET models including FAO-56 Penman-Monteith (PM), ASCE PM. FAO-24 Penman, Kimberly-96 Penman, SCS-93 PM, Penman-48, and the Hargreaves-Samani equations all for grass; the ASCEPM and Kimberly-82 Penman equations for alfalfa (Medicago sativa L.); and the general Priestley-Taylor equation for non-advected conditions were evaluated and contrasted with the daily grass ET measurements. Measured fescue daily ET rates exceeded 10 mmd~(-1) occasionally. The FAO-56 and ASCE Penman Monteith equations tended to over-estimate during spring and fall and under-estimate during summer and especially on high ET days (> 8 mm d~(-1)). The older Penman formula ET correlated well to the measureddaily data. The Hargreaves-Samani and Priestley-Taylor equations substantially under estimated grass ET in this environment.