Date of Award:

5-2026

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Burdette Barker

Committee

Burdette Barker

Committee

Lawrence Hipps

Committee

Bethany Neilson

Committee

Alfonso Torres-Rua

Abstract

Alfalfa is one of Utah’s most important crops, but it is also the largest agricultural consumer of water. Because the state faces frequent droughts and growing pressure on limited water supplies, farmers and water managers are increasingly interested in irrigation systems that could reduce water use. Subsurface drip irrigation (SDI), which delivers water directly to plant roots through buried drip lines, has shown promising results in other regions, where it often reduces water consumption and increases yield. However, little research has evaluated SDI under Utah’s unique climate, soils, and high-elevation valleys.

This study compared an SDI system with a traditional wheel-line sprinkler system in two neighboring alfalfa fields in Richmond, Utah, during the 2024 growing season. To measure crop water use (evapotranspiration, ET), the project used an eddy covariance (EC) tower, LI-710 ET sensors, and satellite-based modeling with the Two-Source Energy Balance (TSEB) approach. Together, these methods provided both detailed short-term measurements and full-season ET estimates.

Unexpectedly, the SDI field used more water than the wheel-line field. TSEB results showed seasonal ET totals of 445 mm for SDI and 410 mm for wheel-line irrigation. The SDI field also produced lower yield, the opposite of what many previous studies have found. Several factors may explain these results. The SDI field experienced stand damage during installation, leaving gaps and reducing early-season canopy cover. A likely shallow water table may have supplied extra moisture, increasing water use. Additionally, the two fields were managed by different farmers using different schedules and practices. Because of these differences, the results should be interpreted cautiously.

Based on this limited dataset, there is no evidence that SDI reduced water use or increased yield at this site. Instead, the study highlights how irrigation performance depends strongly on local soils, groundwater conditions, and management practices. More controlled, multi-year studies are needed before making statewide conclusions about SDI in Utah.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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