Automatic irrigation, controlled by instruments capable of detecting moisture needs of plants, has been successfully used to study evapotranspiration rates for turfgrass at Riverside. Tests indicated that frequent, automatic sprinkling with relatively low-volume applications per irrigation might allow easy measurement of evapotranspiration. Tensiometers, acting as hydrostats, can turn “on” irrigation water when needed, but unpredictable flow rates in soils make it necessary to use a separate timing mechanism to set the duration or amount to be applied and turn the water off. Automatic irrigation management programs are now feasible, under many conditions, using tensiometers or other instruments responding to an energy variable of water in the soil. However, to be accurate for evapotranspiration measurements, such procedures should account for water losses below the rooting depths in the soil.

Funds for purchasing irrigation equipment were provided by the Water Resources Center, University of California, Los Angeles. Moist O'Matic, Incorporated, Riverside, California, contributed to the installation of the automatic sprinkler system.