Semester

Spring

Date of Graduation

2026

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Division of Plant and Soil Sciences

Committee Chair

Eugenia Pena-Yewtukhiw

Committee Member

John Grove

Committee Member

Michael Gutensohn

Committee Member

Joe Lynch

Abstract

Over the past decade, soil health (SH) has gained popularity due to the novelty of sustainable soil use related to human wellbeing. Soil health describes the overall quality of soil and its capacity to function over time. As interest in SH grows, researchers continue to explore new soil health indicators that can improve knowledge on how soil health is assessed and managed. Some indicators directly reflect soil health status, and some indirectly relate to processes and functions occurring within the soil. Volatile organic compounds (VOCs) are naturally occurring compounds that play a role in multiple soil processes. They are associated with both abiotic and biotic soil processes, and are influenced by soil properties such as water retention, soil porosity, organic matter, and microbial activity. It was hypothesized that soil health, categorized as either good (healthy) or bad (unhealthy) is related to the overall quantity and/or type of VOCs. Specifically, soils with “good” SH would produce a higher diversity and concentration of VOCs. Samples were collected from two contrasting plant-soil production systems (pastures and high tunnels). Sampling locations were selected based on farmer-defined soil health levels (good/healthy and bad/unhealthy). Samples were collected at 0-15 cm soil depth, and 4-8 mm dry sieved aggregates were placed in glass vials. The VOC were collected using Stir Bar Sorptive Extraction (SBSE) and analyzed using gas chromatography-mass spectrometry (GC-MS). The VOCs data were compared with other soil properties, including soil pH, dry and wet aggregate stability, soil texture, organic matter, and soil respiration. Results showed a significant interaction between soil health category and production system for the number of unique VOCs (p = 0.1187) at a = 0.15. No significant interactions were observed for total VOCs concentration (p = 0.99). With good SH, the number of VOCs was correlated with clay content, aboveground biomass, bioavailable phosphorus (P), and permanganate oxidizable carbon (PoxC). Aboveground biomass, clay content, and PoxC were also correlated with total VOCs concentration in soils with good SH. With bad SH, only wet mean weight diameter (WMWD) of aggregates was correlated with the number of VOCs. In contrast, sand content, P, and PoxC were correlated with total VOCs in soils with bad SH.

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