high frequency irrigation control necessitates real-time monitoring of soil water, plant water status or atomospheric evaporative demand. the research objective was to determine the suitability of real-time control of subsurface drip irrigation using automated evaporation pan measurements. hourly electronic measurement of water loss from an evaporation pan was a critical feedback control element in the irrigation scheduling of a high frequency subsurface drip system (sdi) used to irrigate cotton. the water level in the class 'a' pan was monitored continuously using a micrologger to measure the output of the electronic water level sensor. the crop water needs were calculated by multiplying the evaporation from the pan by a pan and crop coefficient. when the calculated water need was equal to or greater than 2 mm (0.08 in.) in 1990 and 1 mm (0.04 in.) in 1991, the micrologger automatically activated the irrigation system. data were automatically transmitted daily to the station computer via telephone. water was added each night to the pan automatically to refill the pan to a constant level. after installation and testing, the control system worked automatically without manual intervention for two growing seasons. (author abstract) 16 refs