Soil Health

What is soil health and why should growers care?

A healthy soil is a living, dynamic ecosystem, able to continuously perform physical, chemical, and biological processes that allow crops to thrive over time. Some of these processes include efficient water retention and infiltration, adequate nutrient cycling, proper aeration, and the ability to support a diverse biological community. Organic matter is at the center of all soil functions; it is a primary source of carbon, which gives energy and nutrients to soil organisms. Organic matter interacts with soil particles to form stable aggregates, which enhances the soil water cycling. Also, soil organic matter is a nutrient source itself and has a high pH-dependent cation exchange capacity which reduces nutrient loss and therefore need for nutrient additions.

Soil Health Study

The University of California Davis (UC Davis) Soil Health and Biodiversity Lab and the North Coast Soil Health Hub (NCSHH) conducted independent studies to assess the variability of soil health indicators across 62 vineyards (32 UC Davis, 30 NCSHH) of the Napa Valley AVA with the collaboration of wine grape growers.

A guide has been developed in partnership with UC Davis, Napa Resource Conservation District (RCD) and the Napa Valley Grapegrowers to assist growers in learning how to take and manage soil samples The results from our joint study are detailed in the report “Soil Health Guide for Napa Valley Vineyards.

Read the Guide

Why is soil health important for Napa Valley vineyards?

Soils are a non-renewable resource essential for sustainable wine grape production. Building healthy soils through sustainable management practices can benefit vine health and productivity in diverse ways. A healthy soil with strong aggregation and good structure will allow adequate water flow and retention that can benefit vine root health and growth, and water and nutrient uptake (Smith et al., 2008; Lazcano et al, 2020).

Napa Valley soils are very diverse with distinctive characteristics encompassing 33 soil series and 6 soil orders. The Valley is home to deep and rich alluvial soils, rocky hillsides, and volcanic soils found in a wide range of topographies. This soil diversity provides the perfect setting to grow a wide variety of wine grapes for multiple wine styles. The Napa Valley currently supports the growth of over 40 wine grape varieties, with Cabernet Sauvignon and Chardonnay being the most widely planted (2022 Napa County Agricultural Crop Report).

Building soil health through vineyard soil management practices that promote the accumulation of organic matter, biodiversity, and soil protection, can build vineyard resilience and longevity. Additionally, these practices could benefit vine health and support wine grape growers’ targeted production goals. Testing soil health indicators across the diverse landscape of the Napa Valley AVA works as a tool to assess the status, including opportunities to build soil health and resiliency in vineyards.

Principles of Soil Health

Soil health can be managed by following a series of basic principles that will preserve the integrity of soils as ecosystems and guarantee the provision of ecosystem services such as nutrient cycling, C cycling, water retention and infiltration, and regulation of biodiversity, among others (USDA NRCS). These basic principles are:

Read more about cover crops and compost

There is no established recipe for soil management practices–no silver bullet exists. Winegrape growers must make smart choices to balance the benefits and disadvantages of soil health management, depending on the local climate and soil conditions, their production goals, and desired ecosystem services during the wine grape cycle.

By envisioning a long-term healthy vineyard farmed with healthy soil practices, growers can avoid any drawbacks reflected mainly in yield losses during such a transition that demands commitment and more awareness of its long-term benefits in the agroecosystem.