From the Field

Dry Farmed Tomatoes are Delicious, and They Can Teach Us a Lot About Agroecological Transitions to Water Scarcity

In a new study, Berkeley Agroecology Lab researcher Yvonne Socolar examines the fungal communities in soil that help dry farm systems flourish.

April 29, 2024

By Austin Price

A video produced by Nolan Kirby of Earthworks Media documents Yvonne Socolar’s research on seven organic farms growing dry farmed tomatoes in California’s Central Coast region.

According to Socolar, much of this study was co-designed by the farmers she worked with — farmers like Jim Leap at the UC Santa Cruz Center for Agroecology, Joe Schirmer at Dirty Girl Produce, and Veronica Mazariegos-Anastassiou at Brisa Ranch, who all had a history with dry farmed tomatoes (Jim Leap had even authored a dry farmed tomato growers guide for the Central Coast). Many of the farmers are listed as co-authors on the paper, and a large portion of Socolar’s research was driven by their questions: How did AMF inoculants affect fruit quality and yield? How deep in the soil profile are the nutrients tomatoes access in dry farm systems? How does the fungal community in the soil change under low irrigation conditions?

The results shed further light on the important relationship between soil health and water.

For one, the AMF inoculants did not improve tomato yield or quality — in fact, in some cases, the introduced fungi harmed tomato quality. AMF is ubiquitous in farm soils, and farms will already have their own AMF community prior to inoculation. “Coming in with an exogenous powder is not actually an effective way to build soil health here,” says Socolar, “because these farms are already building a healthy soil microbial community through diversified farming practices like cover cropping and rotating crops.”

These healthy soil communities extend beyond AMF as well. Socolar’s study found that dry farm soils have a unique fungal signature that builds the longer they have been dry farmed. And this signature not only builds, but actually improves tomato quality. “This may be one of the most exciting results for farmers, who now have a new way to promote high quality fruits in their fields by dry farming for multiple years in a row,” says Socolar.

In a recent study, Yvonne Socolar researched the fungal communities known as arbuscular mycorrhizal fungi that may help tomatoes access nutrients under water stress. Here, Socolar collects soil samples to bring back to the lab. Photos by Nolan Kirby

In February 2023, Socolar organized a symposium that gathered farmers in the Central Coast region of California to discuss dry farming.

Socolar also noted that dry farmed tomatoes send their roots deep into the soil — usually more than two meters down, and much deeper than a farmer will typically manage for nutrients. Socolar’s study found that, because surface soils dry quickly in dry farm systems and effectively lock those nutrients away from plant roots, dry farm tomatoes use their deep roots to draw nutrients from depths of two feet and below. That knowledge signals that farmers may have success experimenting with several seasons of deeply rooted cover crops like daikon radish to build up nutrients deep into the soil.

In the context of these farms in Santa Cruz and San Mateo counties, dry farming works well not only because the conditions are right — the Central Coast rarely gets too hot; it receives a lot of winter rain; the soil has the right clay content to hold onto moisture — but also when farmers take care of the soil in a way that both primes tomatoes for low irrigation and adapts them to the conditions. As opposed to irrigated tomato agriculture across the state, diversified, dry farm systems on the Central Coast exemplify place-based, agroecological farming.

“This is a celebration of diversified farming,” says Socolar. “ Dry farming isn’t a silver bullet, but it can be a lighthouse example for how diversified farming practices can help farmers decrease water usage — even if it’s not all the way to zero irrigation — and become more suited for the environmental conditions where they’re growing.”

This research was supported by the USDA National Institute of Food and Agriculture through the Western Sustainable Agriculture Research and Education program.

Learn more about this research and dry farmed tomatoes: