Nighttime scheduling of sprinkler irrigation is a widespread strategy to conserve water by reducing wind drift and evaporation losses (WDEL). Water intercepted by a canopy and evaporated during daytime irrigation events, however, may decrease gross water loss and ease heat stress, while microclimate changes from nighttime irrigation may be less consequential. The objectives were to determine whether water savings exist when comparing daytime versus nighttime irrigation with two urban crops by measuring (1) field water- and energy-balances to quantify WDEL, crop evapotranspiration (ETc), and changes in soil moisture storage; (2) the response of microclimate and evaporative demand; and (3) crop response. A field study at the Greenville Research Farm in North Logan, Utah (41.77° N, 111.81° W), tested two sprinkler irrigation timings (daytime, 14:00–17:00, and nighttime, 02:00–05:00) with Poa pratensis L. ‘Kentucky bluegrass’ turfgrass and Zinnia elegans L. ‘Benary’s Giant Salmon Rose’ cut flowers, in triplicate from 2019–2021, resulting in 126 paired events. The mean WDEL were 7% greater with daytime irrigation than with nighttime irrigation across both crops. Using the field water-balance method, the mean total seasonal ETc, was 13 mm greater with nighttime irrigation than with daytime irrigation for both crops. There were no significant differences in ETc using the energy-balance method, nor was the response of either crop significantly different by day/night irrigation timing. Though recommendations may vary by climate and sprinkler design, landscape irrigation should avoid hours with wind speeds greater than 3 m·s− 1 and not rely on nighttime irrigation as a sole water conservation approach.
Pyakurel et al. (Fri,) studied this question.