Publication Date

5-2021

Date of Final Oral Examination (Defense)

3-12-2021

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geoscience

Department

Geosciences

Major Advisor

David Wilkins, Ph.D.

Advisor

Jennifer Pierce, Ph.D.

Advisor

C.J. Northrup, Ph.D.

Abstract

Terroir is the set of factors including climate, soil, and management practices that influence the character of a wine. Of these factors, soil texture and chemistry is a major determinant in wine grape quality (van Leeuwen et al., 2009). Understanding the characteristics of the soil is key to making decisions that support the production of the highest possible quality grapes from the resources available. Few studies have been conducted in the Snake River Valley AVA (SRVAVA). This study seeks to build upon the data already available and provide analysis of vineyard-scale terroir in a leading grape growing district of the SRVAVA.

Nine vineyards from the Sunnyslope wine grape growing district of southwestern Idaho were selected for their diversity of geographic location and growing environment. Soil pit locations in each vineyard were determined using a stratified-random sampling technique and normalized difference vegetation indices (NDVI) calculated from aerial imagery. This study combines field collection, sampling and analyses of soil texture and chemistry to characterize the soils in the selected vineyards. The results show the majority of vineyards contain aeolian or colluvium-derived soils composed of coarse silts and fine sands. Only two vineyards, those located closest to the Snake River, contain basalt gravels and lithic sands not observed in the other vineyards. Geochemical data show an increase in Ca with elevation and a decrease in Fe and Mn with elevation, which may be the result of varying soil parent materials or recent deposition of sediments.

The results of my study support the presence of vineyard-scale terroir and the assertion that intra- and inter-vineyard heterogeneity is inherent. Further, my results show recent sediment deposition and agricultural practices have overprinted the original soil profiles. Understanding vineyard-specific soil characteristics like those investigated in this study will allow vineyard owners to manage for specific soil traits and promote the unique terroir of their product. Management of vineyards in this way can support the growth of high-quality grapes and the production of desirable wines that reflect the unique conditions under which they were grown, their terroir.

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