Evapotranspiration Note

This technical note treats plant water need as two parts, the water held in the plant's own tissue and the water lost by transpiration, and sets out the metered EPIC records that show how much turf draws from a stable underground reservoir.

Transpiration varies with species, leaf area, humidity, temperature, wind, sun and plant health; the note gives turf rates from 0.10 gallons per ft² per day on cool nights to over 0.40 in hot, dry, windy conditions. It sets out textbook water requirements by climatic region, from foggy coastal climates to dry desert areas, and explains why overhead sprinkler irrigation is inefficient.

The test records include a sand-based Kentucky bluegrass bucket logged in Reno in August and September 2001, with period averages of 0.17 to 0.24 gallons per ft² per day, and the University of Nevada, Reno practice field of 200,000 ft², metered from July 2000 to May 2002 with monthly averages of 0.09 to 0.16 gallons per ft² per day.

The note closes with three comparisons: a four-year residential study in Reno (0.15 gallons per ft² per day for EPIC against 0.33 for sprinklers, stated as 58% less), a New Mexico State University study on 12 golf greens reporting 50% savings with better turf quality, and Al Sammaleah Island in Abu Dhabi, where Bermuda grass in an EPIC profile used 78.9% less water than a similar area under conventional sprinklers.