Date of Award

8-2026

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

Committee Chair(s)

J. Burdette Barker (Committee Chair)

Committee

J. Burdette Barker

Committee

Alfonso Torres-Rua

Committee

Scott B. Jones

Abstract

Growing water scarcity in the Intermountain West has increased interest in improving water use efficiency. Subsurface drip irrigation (SDI) has the potential to reduce evapotranspiration (ET), evaporative losses, surface runoff, and deep percolation. SDI adoption in Utah forage crops is limited, and region-specific information on forage crop water use under SDI is lacking. This study compared ET, yield, and productivity of forage crops between SDI and conventional irrigation methods in northern Utah.

The study was conducted on production fields. Applied irrigation, precipitation, and crop yield were directly measured, while deep percolation was estimated using numerical unsaturated flow modeling. Surface runoff was estimated using the Soil Conservation Service method. Weather data were collected from an on-site weather station.

Mean seasonal ET under SDI (550 mm) appeared lower than under conventional irrigation methods (665 mm). However, the difference was not statistically significant. Mean seasonal dry crop yield on SDI (5.4 Mg ha⁻¹) was significantly lower than under conventional irrigation methods (10.1 Mg ha⁻¹; p = 0.01). Mean crop water productivity under SDI (9.8 kg ha⁻¹ mm⁻¹) was lower than in conventional irrigation methods (15.2 kg ha⁻¹ mm⁻¹). Lower yield under SDI was likely due to crop stand damage during drip lateral installation and uncertainty in grower-reported yield values. SDI did not reach the goal of increasing crop yield and crop water productivity compared to conventional irrigation methods. Therefore, installing SDI into existing alfalfa stands is not recommended. Additional studies across more SDI sites conducted over complete growing seasons are warranted to evaluate irrigation effects on seasonal ET.

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