IRRIGATION SCHEDULING ON SAND-BASED CREEPING BENTGRASS Evaluating ET Estimation, Capacitance Sensors and Deficit Irrigation in the Upper Midwest

During the 2003 and 2004 growing seasons, research was conducted on a 'Providence' creeping bentgrass (Agrostis stolonifera L.) sand green at the University of Minnesota St. Paul campus to evaluate the use of ECH20 capacitance soil moisture sensors and FAO 56 ET (Food and Agriculture Organization of the United Nations Evapotranspiration) estimation in scheduling turfgrass irrigation by applying prescribed irrigation treatments based on replacement of 100% actual ET loss and either 100% or 80% of FAO 56 estimated ET loss in a series of four 10 day experiments. Turf quality and soil moisture response to deficit irrigation treatments were also assessed. FAO 56 ET estimation accurately predicted actual ET, and a summer crop coefficient (kc) of 0.98 was calculated. ECH20 probes were highly sensitive to changes in soil moisture. There were no significant differences in root zone water storage fluctuation between treatments. Lysimetry and sensor data indicated the presence of a substantial thatch effect on irrigation infiltration and ET loss. Daily irrigation consistently wetted the soil no deeper than 10 cm. There were no statistical differences in turf quality between irrigation treatments in any experiment, suggesting that replacement of 80% of actual ET is sufficient to maintain acceptable daily irrigated creeping bentgrass in Minnesota.