| Summary: | Turfgrass actual evapotranspiration (ET) measurements are critical for water management and irrigation scheduling. With no historical ET measurements in eastern North Dakota, turfgrass ET rates were measured with the residual method using eddy covariance instrumentation and two arrays of soil moisture sensors on unirrigated turfgrass under natural conditions in the 2011, 2012, and 2013 growing seasons. An on-site weather station provided weather data to calculate the standardized grass-based reference evapotranspiration (ET) (). The daily ET/ET ratios were screened using the criteria of soil moisture ≥50% of available water for the top 30 cm of the root zone, rain amounts ≤10 mm, and a recovering period after drought. The screened monthly average ET/ET ratios for the unirrigated turfgrass were 1.03, 0.98, 0.94, 0.90, 0.82, and 1.18 from May to October. The mean ET/ET ratio for the entire growing seasons was 0.96, implying that the American Society of Civil Engineering–Environmental and Water Resource Institute ET method was valid for guiding the turfgrass ET calculation even in unirrigated and cold climate conditions. Because this is the first reported study on ET measurement of a turfgrass site, the limited data can provide a baseline on water management for turfgrass under various weather conditions in this region. The results indicated that a monthly refinement of ET/ET values might be required to maintain the landscape turfgrass quality more precisely in terms of water management.
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