Soil health is essential for agricultural adaptability and sustainability to climate change challenges. While soil health has been extensively studied in temperate annual agroecosystems with yield maximization goals, it remains understudied in semi-arid irrigated vineyards with unique production goals. This dissertation includes a participatory and multidisciplinary approach to assess the variability of soil health in vineyards. Integrating grower insights and scientific assessments, these three interconnected studies collectively address the complex relationship and variability of soil health practices, indicators, and microbial diversity in vineyards. The first chapter is composed of a “needs assessment” that evaluated wine grape growers’ perceptions and attitudes of soil health through semi-structured interviews. Growers defined vineyard soil health as a balanced, biodiverse, and resilient ecosystem that supports high-quality grape production. Barriers such as economic risks and knowledge gaps hinder the adoption of soil health practices, especially among Late Majority growers, emphasizing the need for targeted outreach and practical, outcome-based research. The second chapter focuses on assessing the variability of soil health indicators, such as those that represent carbon, nutrient and water cycling functions as well as microbial diversity, across grower-defined challenging and ideal soils in vineyards. Soil texture emerged as a key determinant of soil health for the growers due to its influence on water cycling functions and perceived effects on vine balance and grape quality. In contrast, disturbance (till vs no-till) practices and vineyard zone (vegetative cover in the tractor rows vs bare and irrigated vine rows) influenced the variability of several soil health indicators. This work underscores the value of incorporating grower collaboration to link soil health assessments with management decisions, particularly those targeting carbon and water cycling. The third chapter investigates the diversity of soil microbial communities and their relationships with soil health indicators in vineyards. Variability in microbial alpha (Shannon diversity index) and beta (Bray-Curtis dissimilarity) diversity was influenced by soil texture, disturbance, and depth. Key soil health indicators, such as TC, MBC, WAS, and NO3--N, correlated with microbial diversity, revealing critical connections between microbial dynamics and soil health functions. Together, these studies illustrate the importance of integrating grower perspectives, soil health assessments, and microbial diversity analyses to enhance sustainable vineyard management, advancing our understanding of grower needs, soil health functions, and their role in viticulture.

The negative effects of population growth and agricultural intensification on soil resources are further exacerbated by drought in arid regions like the California Central Valley. Deficit irrigation management techniques are used to navigate water shortages and work to maintain adequate production while limiting water inputs. This thesis examines the effect of four deficit irrigation management schedules via subsurface drip on the physicochemical properties of soil cropped with processing tomatoes, a late-season crop commonly grown under deficit irrigation. First, I investigated soil physical and chemical properties over the course of the season as the soils were exposed to increasing water stress. Second, I investigated the spatial arrangement of microbial populations and variability of soil physicochemical properties as the wetting zone of the soil decreases throughout the season. The experiment occurred in two consecutive years, 2021 and 2022, in Five Points, California. Processing tomatoes were irrigated with a control treatment, or either low, medium or high water stress treatments, each replicated three times. Soil physical and chemical properties such as pH, electrical conductivity, microbial biomass carbon, nitrate nitrogen, ammonium nitrogen, and potentially mineralizable nitrogen were measured in both experiments four times throughout the season. Spatially, I analyzed phospholipid fatty acid groups in the soil at 10 cm, 25 cm, and 45 cm away from the irrigation emitter. In both years, tomato yields did not significantly differ between the deficit irrigation treatments. Nitrate-N decreased as the season progressed, while potentially mineralizable nitrogen and ammonium-N increased with distance from the irrigation emitter. The total concentration of bacteria decreased with distance from the irrigation emitter in the medium stress deficit irrigation treatment, but not substantially more so than in the other irritation treatments, and our measured concentrations did not fall below ranges of total bacteria found in previous literature. I conclude that deficit irrigation does not significantly impact yield in processing tomatoes or reduce other soil properties such as pH, potentially mineralizable nitrogen, and microbial biomass carbon, sufficiently enough to affect soil health.