INSIGHTS INTO TERROIR FACTORS FROM A DENSE NETWORK OF VINEYARD SOIL AND WEATHER STATIONS, SUNNYSLOPE DISTRICT, IDAHO

The Sunnyslope District (District) of the Snake River Valley Appellation is the focus of wine grape production in Idaho. The District covers roughly 4,000 ha of the interfluve between the Snake and Boise rivers to the west and southwest of the city of Boise, with approximately 430 ha under vine. The District has varied physiographies including exposed Plio-Pleistocene-aged lake deposits, remnant Pleistocene-aged river terraces and volcanics, and Bonneville flood deposits. In 2014, we initiated a study of the District’s terroir that focused on the soils and climate at 10 vineyard site. Eight of the ten vineyard sites are within a 5.5 km radius and so present an opportunity to examine how terroir factors vary over short distances. Soil pits were dug at 17 locations, and 10 weather and soil moisture stations were established. Here we present data and observations that show how slope, aspect, elevation, and distance from the Snake River may be factors in distinguishing between the vineyard sites.

Soils are all Entisols or Aridisols, dominated by sand, sandy loam, or loamy sand, and are well to exceptionally-well drained. Profiles and parent materials are split evenly between soils with simple profiles and single parent material, soils having buried and sometimes restrictive horizons, and soils with strongly contrasting, and sometimes cobbly, layered parent materials. Soils with simple profiles tend to occupy lower elevation sites while sites with buried or more complex layering are higher up the interfluve. Sites that are lower in elevation are also typically cooler (fewer growing degree days). The instrumentation also revealed differences between sites with respect to cold damage vulnerability - this difference is attributable to differences in potential for cold air to drain from vineyard sites. The winter of 2016-17 in the District was extreme by all measures, breaking records for snow on the ground as well as near record low temperatures. Sites that had both higher gradient slopes and space to accommodate cold air drainage recorded less extreme cold temperatures (-26°C) than sites with no to low gradient slopes with no space to accommodate cold air drainage (-31°C). Differences between sites provide data that, in future plantings, may inform selection of cultivar choice to fit the characteristics of the vineyard.