Hopes of dry land: Managing soils to improve fruit yield and quality in dry farm tomatoes

View the project final report

Commodities

• Vegetables: tomatoes

Practices

• Crop Production: biological inoculants, drought tolerance
• Education and Training: farmer to farmer, on-farm/ranch research, other, participatory research, workshop
• Natural Resources/Environment: biodiversity
• Production Systems: agroecosystems, dryland farming, organic agriculture
• Soil Management: soil analysis, soil chemistry, soil microbiology, soil quality/health
• Sustainable Communities: community development, public policy

As farmers confront the fragility of California’s water system, a crucial question emerges: how can farmers adapt to water scarcity without jeopardizing their livelihoods? Innovative farmers have turned to dry farming, a method of growing produce with little to no external water inputs, and a radical departure from irrigated agriculture. Conversations with six such farmers in the Central Coast region reveal strong interest in research that evaluates the soil microbial and nutrient factors that can best support dry farm crops.

We propose to assess how farmers can shape soil microbial communities through fungal inoculants and nutrient management in ways that enhance dry farm tomatoes’ performance. Recent trials have established fungal inoculants as tools to alleviate crop water stress, making them ideal candidates for dry farm soils; however, high soil nutrient concentrations deter plant-fungal symbioses. Through participatory research we will measure soil nutrients and plant-fungi symbioses to determine whether inoculation can profitably improve fruit yields and quality, and under what soil nutrient conditions.

We will also help facilitate a dry farming community of practice by collaborating with participating producers and local ag advisors to organize a producer workshop, encouraging attendance among experienced and potential new dry farmers in addition to local land and groundwater policy stakeholders. Our findings will be shared through presentations at conferences, and in videos, factsheets, op-eds, and a peer-reviewed publication. Through increased awareness and improved techniques, we hope to grow the practice of dry farming, preserving water as we build the dry farm community.

1. Coordinate field trials through on-farm participatory research to engage farmers in research design and outcomes. In Spring 2021 we began on-farm trials on seven dry farm tomato fields after having engaged in a participatory design process with dry farmers on California’s Central Coast. These farmers have a shared interest in identifying management practices that can limit blossom-end rot and increase yields, leading us to focus our study on how to manage dry farm soils to encourage fungal symbionts that show potential to improve both fruit yields and quality. The project allowed us to collect labor-intensive harvest data from the indeterminate tomato varieties grown on the fields, and to analyze soil/root samples to provide farmers with information on how to best manage dry farm soils to support beneficial fungal communities.
2. Characterize fungal communities and quantify the utility of fungal inoculants. Our project builds on promising preliminary trial results with arbuscular mycorrhizal fungi. We set up five inoculated and five non-inoculated plots in each field to determine which native fungal species are present and deepen our understanding of the relationship between fungal diversity and improved farm production, while testing whether fungal inoculation has the potential to improve tomato performance on dry farms. 
3. Identify soil management strategies that enhance fruit yield and quality, and evaluate their profitability. Because high nutrient concentrations can limit plant-fungi associations, we tracked soil nutrient levels (nitrogen and phosphorus, both available and total) to pair with fungal and harvest data. Of particular interest is nutrient depth, as some farmers go to great lengths to deliver nutrients deeper into the soil profile in dry farm systems. Also of interest is field history—i.e., number of years since most recent irrigation—as previously dry soils may prime native beneficial microbial communities. We will identify the soil management strategies (inoculation, nutrient depth, etc.) that show the strongest yield/quality improvements, and compare farm revenue generated by each practice to expected management costs to determine profitability.
4. Engage Central Coast farmers and stakeholders in collaborative learning about dry farm soil management. We maintained a blog over the course of the field trials to build connections between participants and maintain engagement in the research process. In the second year of the project, after data have been analyzed, our producer workshop will allow farmers to connect with research results, one another, and relevant land and water stakeholders.
5. Disseminate findings to build the dry farm community and public engagement. A video we produce, two conferences, a factsheet, and the producer workshop will help us communicate our results to producers, improving dry farm soil management, lowering barriers to beginning dry farmers, and introducing new farmers to the practice. A policy memo and a publication for a general audience will increase public interest in dry farming, as well as potentially shaping policy to incentivize the practice.