Potential Evapotranspiration, ETo (also abreviated as PET), is an estimate
of the water requirements of a 4-inch grass growing
in a deep soil under well-watered conditions. A turf
coefficent (Tc) is needed to relate pET to the water
requirements of a specific turf. For established lawns,
the Tc remains constant throughout the active growing
season of the grass. For warm season grasses, such
as St. Augustine, the Tc is 0.6 throughout much of
the year, while the Tc for cool season grasses, such
as rye, is 0.8.
However, we seldomly apply this amount of water to
lawns. Why? Because we do not want maximum production
of grass clippings. Instead, we want to maintain a
healthy, attractive turf with as little water as possible.
Thus, we modify the coefficent by specifying a Quality Factor.
The complete equation is:
ETo x Tc x Qf = turf water requirement
