Date of Award:

5-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Melanie Stock

Committee

Melanie Stock

Committee

Scott Jones

Committee

Neil Allen

Committee

Kelly Kopp

Abstract

Nighttime irrigation scheduling is a longstanding water conservation approach to reduce evaporative losses in Utah's semi-arid, urban landscapes. However, residential demand now exceeds system capacity, and the efficiency of the practice has come under question. Therefore, the objectives of this study include: 1) quantify whether a water savings exists between day and night irrigation with a water balance and energy balance approach, and 2) analyze microclimate and crop quality effects to determine any changes to evaporative demand or plant stress by irrigation timing. In 2019, we established 12 field plots in North Logan, UT (41.77° N, -111.81° W, 1380 m elevation) to test two irrigation timings (2:00 - 4:00 am and 2:00 - 4:00 pm) with two urban crops (turfgrass and zinnia cut flowers) on a sprinkler system in triplicate. Field instrumentation included a central weather station, flow meters on sprinkler sets, soil moisture sensors at 0.08 m and 0.18 m depths, canopy air temperature and vapor pressure, surface temperature, and catch cups for wind drift and canopy interception calculations. Daytime irrigation resulted in greater wind drift and evaporative losses (WDEL) by 7% compared to nighttime in both crops. A decrease in canopy and surface temperature, as well as the vapor pressure deficit was greater with daytime irrigation than nighttime, decreasing the evaporative demand at maximum air temperature (Tmax). Turf and zinnia yield and quality were not affected by irrigation timing, though the percentage cover of turf was significantly greater with daytime irrigation compared to nighttime. Thus, landscape irrigation scheduling should avoid hours with peak wind speed to reduce the WDEL and irrigate the field at or after Tmax to reduce the evaporative or heat stress to the crop.

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