Determining Irrigation Thresholds Using Plant Available Water By: Ryan Schwab, Josh Friell, Eric Watkins, Gabe Olson-Jensen University of Minnesota
Irrigation practices that allow for depletion of soil water until just prior to the onset of visual wilt have historically been recommended for turfgrass soil water management because they encourage deeper rooting and greater resilience to drought stress (Espevig & Aamlid, 2012; Fu & Dernoeden, 2009; Fu, Fry, & Huang, 2007). Moreover, maintaining somewhat drier conditions is likely to produce a firmer, faster golf playing surface. Reports of water savings and improved playing conditions produced by using light and infrequent irrigation applications have drawn interest (Woods, 2013), but require further investigation. Fortunately, multiple technologies are available that enable practitioners to make data-driven irrigation decisions that can remove some of the 50
uncertainty associated with these approaches. Evapotranspiration (ET) is used to schedule irrigation using a water balance approach; however, it is sparsely used in the Midwest and the accuracy of ET estimates can be questionable. Conversely, in-ground soil moisture sensors (SMS) provide a real-time point measurement of available water. They may be placed in multiple representative locations across a golf course (Straw, Friell, & Horgan, 2019) and have been shown to generate significant water savings when used for irrigation scheduling and control (Serena et al., 2020). The use of SMS is formalized in the practice of threshold-based irrigation. Threshold-based irrigation is not a new concept and has long been used in agriculture. This approach is