Assessment of the Variability in Soil Health Indicators and Incorporating Healthy Soil Management Practices into the Context of Napa Valley Terroirs

Adoption of sustainable soil management practices is becoming common in winegrape production in response to an increased awareness of the value of soil health to maintain environmental quality. Soil health is characterized by the functions it provides to the vineyard (i.e water retention, nutrient supply, carbon sequestration etc.) and is often impacted by vineyard floor management practices such as compost application, no till or the use of cover crops. However, the magnitude of the effect of healthy soil practices on soil organic matter and other soil health indicators is difficult to predict. A major impediment for the diagnosis and establishment of target values of soil health in vineyards is the large diversity of soils and physiographic conditions across and within growing regions. In this project, we carried out semi-structured interviews to growers paired with ongoing sampling efforts across 32 vineyards in Napa Valley to (i) establish a baseline of soil health indicators within the various Napa Valley soil types; and (ii) examine grower perception and comprehension of these indicators and the desired qualities of a healthy soil relative to production goals. Activities in this project were carried out though a collaboration between researchers, extension specialists and the Napa Valley Grapegrower Association. The data gathered so far shows that most grape growers consider soil health to be important for wine grape production due to perceived benefits to reduce soil erosion, improve vine health and grape quality. Through grower input, researchers were able to extract the soil properties that are the most important for these beneficial outcomes, namely a balanced soil structure and nutrient supply. Finally, data collected in the interviews revealed a strong grower knowledge of how the physical and chemical aspects of soil health are related to beneficial agronomic outcomes, as well as strong grower interest in understanding the role of soil organic matter and the soil biome on these outcomes. The research team is currently collecting soil samples to assess the variability and establish benchmarks for those soil health indicators that are desired for winegrape production. Furthermore, we will assess the role of soil organic matter and the soil microbiome with these indicators of soil health.