In the summer of 1993, I visited the two small farms on the campus of UC Santa Cruz (UCSC). One of them was a flat, sunny site near the coast, the air pleasantly warm instead of blistering hot like further inland. The tour guide showed us a field in which small, round, bright-red tomatoes peeked out from brown, withered, un-staked vines. I felt appalled to see a UC growing tomatoes so incorrectly.
The tour guide then extracted some of the red globes from the brown rubble of vines and gave each of us one to try. The juicy tomato erupted with deep, complex flavor and sweetness. Feeling disloyal to the Jersey tomatoes I had enjoyed every summer growing up, I had to admit that this was the best tomato I had ever tasted. It still is 33 years later. I happily revised my opinion of the UCSC farming methods.
The tour group leader explained that the tomatoes were dry farmed, meaning that they were grown with only the water that the soil absorbed the previous winter. The tomato vines did not need staking because the dry surface of the ground was inhospitable to harmful insects and fungi.
The lack of water concentrated the flavor and sugars into a smaller volume. As researcher, Yvonne Socolar said at a recent dry farming webinar, “Dry-farmed tomatoes and grapes taste incredible, and consumers are willing to pay for that. But most dry-farmed crops don’t have a quality bump, so it is not a slam dunk for dry farming.”
However, dry farming is getting more attention across California as growers look for ways to farm in a water-constrained environment. But what does dry farming actually involve, where does it work well and what are the tradeoffs?
The dry farm webinar, sponsored by the Berkeley Food Institute, dug into those questions. Socolar — one of two presenters — noted that the changing climate is making the water supply in California less predictable, and 16% of California’s main groundwater systems are running dry.
As in other Mediterranean climates, rain falls mainly in the cool winter season and typically not at all in the summer growing season. Dry farming of tomatoes occurs in coastal areas but potentially could work in parts of the western foothills of the Sierras. By contrast, the inland valley floors are too hot and dry.
Socolar presented a map of suitable locations for dry farming in California that she generated based on interviewing dry-farm tomato growers. The map can be seen in her research paper at Where dry farming could work in CA. Fortunately, the high priority water areas do have land suitable for dry farming.
How Do the Plants Survive?
Socolar explained that dry farming is inherently a diversified farming system, with cover cropping and hedgerows complementing the crop. The plants need deep roots in soil that holds moisture. Organic matter from cover crops is central for holding water and creating a conducive microbiome.
Although not widely used yet, biochar can also hold water, and it does not break down, so it might help even in years when the cover crop does not thrive. Cover crops, however, also provide nutrients. Foliar sprays also may be used to distribute micronutrients.
Eight of the 10 farmers who Socolar interviewed also rotate crops, but two do not, growing tomatoes repeatedly (10 years in a row and counting), or switching between tomatoes and fallow.
Socolar wrote in her article, “These management decisions to maintain fields as dry farmed rather than rotating irrigated crops through are particularly compelling in light of recent research on many of the same fields, showing that repeated seasons without any external irrigation result in soil microbial communities that are associated with improved dry farm tomato performance.”
Water Savings
The dry-farm methods used in California come from Greece and Spain, which have the namesake Mediterranean climate. Whereas the average water consumption for irrigated crops on typical dry-farm land is roughly 3 acre-feet per acre, most dry-farm tomato growers use between zero and ten inches of water.
Socolar estimates that nearly half of the water of the Shasta reservoir could be saved — 776 billion gallons/year — if all the potential dry farmland were dry farmed.
Built-In Pest Control
Because the surface of dry-farmed soils is dry during the growing season, weeds, pests and diseases have a harder time gaining a foothold. That lessens the need for labor. “Weed seeds need water to germinate, so they don’t emerge as easily, and fungal diseases that thrive in moisture do not have the conditions they need to take hold and spread,” Socolar described.
But Socolar cautions that not all that potential dry-farm land is ready to be dry farmed immediately. Rehabilitation with cover cropping and incorporating green manure may take years before the field reaches the level of performance needed to dry farm.
For farmers renting land, the lease term would need to be at least ten years to make the investment in soil benefits worthwhile and so the farmer can get to know the fields. The grower also needs a market willing to pay the quality premium.
Socolar notes that some farmers have also found nuts and orchard fruits to be desirable options to add to tomatoes and grapes for dry farming. “These crops have similar market appeal and quality premiums, making them economically viable,” Socolar wrote. Olives, too, being from the Mediterranean area are traditionally dry farmed, and were grown without irrigation until the 1970s. Globally, by far most olive oil crops are still dry farmed, according to Leandro Ravetti of Cobram Estate Olive Oil.
Whatever the crop, the current dry farmers are paving the way for viable options for other California farmers as the squeeze on water tightens.
— By Nancy Power, Assistant Editor