TO: Technical Advisory Group for the Napa County Groundwater Sustainability Agency
FROM: Brian D. Bordona, Director of Planning, Building and Environmental Services
REPORT BY: Jamison Crosby, Natural Resources Conservation Manager
SUBJECT: Presentation on Soil Health and Water Storage Assessment in Dry-Farmed Vineyards
RECOMMENDATION
title
Miguel A. Garcia PhD, Senior Project Manager, Agriculture, Resource Conservation District of Napa County, will make a presentation to the TAG on a regional soil health and water storage assessment in dry-farmed vineyards funded by the California Department of Water Resources to better understand and promote dry-farming practices for water conservation and climate resilience.
body
Procedure
Staff introduces.
Questions and answers with the TAG.
Public comments.
BACKGROUND AND DISCUSSION
Dry farming has long been practiced in California and plays a critical role in supporting agricultural resilience under conditions of increasing water scarcity and climate variability. This presentation summarizes findings from a regional soil health and water storage assessment conducted across 15 dry-farmed vineyards in Napa, Sonoma, and Mendocino Counties. The project seeks to evaluate how soil management practices influence soil health and the capacity of vineyard soils to store and supply water throughout the growing season without in-season irrigation.
Soil pits were sampled during the 2025 growing season to assess physical, chemical, and biological indicators of soil function, including organic matter, aggregate stability, and plant-available water. Various vineyard management practices were assessed from reduced- or no-till systems with organic inputs to more intensively tilled operations, allowing comparison of how disturbance and soil stewardship practices affect water storage and soil resilience.
Results indicate that most fields functioned within or above expected soil health and water-holding ranges relative to soil texture. Subsoil horizons consistently served as late-season moisture reserves, supporting vines through the dry season. Overall, the findings demonstrate that well-managed dry-farmed soils can function as effective natural water reservoirs, reinforcing the role of soil health in agricultural resilience and long-term groundwater sustainability.
ENVIRONMENTAL IMPACT
ENVIRONMENTAL DETERMINATION: The proposed action is not a project as defined by 14 California Code of Regulations 15378 (State CEQA Guidelines) and therefore CEQA is not applicable.
SUPPORTING DOCUMENTS
A. Presentation on Soil Health and Water Storage Assessment in Dry-Farmed Vineyards (Dr. Miguel Garcia, Napa RCD)