UC Food Blog
What flavors do you detect in a sip of lemon water? Are there notes of sweetness, sour, off flavors or fresh citrus taste? Scientists at the UC Kearney Agricultural Research and Extension Center and the USDA want to know every subtle taste sensation for a research project continuing over the next 18 months.
Participants will taste the major types of citrus to confirm that treatments used to eliminate pests in overseas shipments don't have an impact on fruit enjoyment. Lemon tasting will be followed by mandarins, navel and Valencia oranges, and grapefruit.
“This work is critical for the citrus industry,” said Mary Lu Arpaia, UC Cooperative Extension specialist in subtropical fruit. “A huge amount of California citrus is exported, but if there are quarantined pests in the shipment, that triggers treatments with a fumigant.”
In the past, importers treated citrus with methyl bromide. However, the pesticide has been phased out because it depletes the ozone layer. An alternative fumigant, phosphine, kills the insects, but scientists don't yet know what impact the chemical will have on the fruit.
“We're hoping there's no taste difference,” Arpaia said. “But we don't know. That's why we're doing the testing.”
USDA plant physiologist David Obenland, based at the USDA office across the street from Kearney in Parlier, is working with Arpaia to conduct the study at Kearney's sensory laboratory. The 1,100-square-foot laboratory features neutral white paint and broad-spectrum lighting; the ventilation system minimizes distracting odors. Six tasting booths each have small windows that open to the kitchen area, where samples are prepared.
“Previous research has resolved residue issues and determined phosphine is effective in killing the pests,” Obenland said. “But they didn't fully determine whether the process would hurt the fruit.”
The current project compares fruit treated with methyl bromide, phosphine and a cold temperature protocol in which the fruit is held just above freezing for three weeks. In addition to tasting the fruit, volunteers evaluate the fruit's appearance.
“People buy with their eyes,” Arpaia said. “We're asking our participants to compare the fruit visually to see if they detect any differences.”
The research is funded by the California Citrus Quality Council through a grant from the USDA Foreign Agricultural Service.
That simple request, prefaced with a term of endearment for good measure, means there's honey on the table.
And well there should be. As the daughter, granddaughter and great-great granddaughter (and beyond) of beekeepers, I grew up with honey on the table. (And on my fingers, face and clothes.)
My favorite then was clover honey from the lush meadows and fields of our 300-acre farm in southwest Washington. My favorite now is Northern California yellow starthistle honey, derived from the blossoms of that highly invasive weed, Centaurea solstitialis, which farmers hate (and rightfully so) and beekeepers love.
“Almost every honey has its own unique flavor-- even when it is the same varietal,” says Amina Harris, director of the UC Davis Honey and Pollination Center. “There are characteristics we learn to look for, but even within that variety, the honey will differ from each area collected. For instance: avocado honey is known for being very dark amber with a flavor reminiscent of molasses, licorice or anise. However, once you start tasting a selection, some will taste like blackstrap molasses and very black licorice. Others will have almost a fruity flavor like dried figs or prunes. Most folks can't tell the difference – and then there are the honey nerds, like me!”
“My favorite all-around honey is one I keep returning to. I love sweet clover from the High Plains with its cinnamon hit —the spicy characteristic is just something I love,” Harris said. “My favorite ‘shock honey' is coriander. Collected near Yuba City, this seed crop gives us a honey that is like walking through a spice bazaar with hints of cardamom, cinnamon, allspice, nutmeg, coriander and — chocolate.”
The UC Davis Honey and Pollination Center, located in the Mondavi Institute for Wine and Food Science on Old Davis Road, periodically offers courses on the sensory evaluation of honey, as well as honey tastings. Next up: the center will host free honey tastings at its home base during the 105th Annual Campuswide Picnic Day on April 13, and at the California Honey Festival in downtown Woodland on May 4. Another popular honey tasting: California Extension apiculturist Elina Lastro Niño, based in the UC Davis Department of Entomology and Nematology, hosts a honey tasting at Briggs Hall during the annual Picnic Day.
There's more to honey than meets the eye — or the palate. The Honey and Pollination Center recently hosted a three-day Sensory Evaluation of Honey Certificate Course last October, using “sensory evaluation tools and methods to educate participants in the nuances of varietal honey,” Harris said. Northern California public radio station KQED spotlighted the course on its “Taste This” program.
And we owe it all to honey bees.
Pollination ecologist Stephen Buchmann of the University of Arizona (who received his doctorate in entomology from UC Davis, studying with native pollinator specialist Robbin Thorp), writes in his book, Honey Bees: Letters from the Hive, that each worker bee “may make four to ten or so flights from the nest each day, visiting hundreds or many thousands of flowers to collect nectar and pollen. During her lifetime, a worker bee may flown 35,000 to 55,000 miles collecting food for her and her nest mates. One pound of honey stored in the comb can represent 200,000 miles of combined bee flights and nectar from as many as five million flowers.”
Take a 16-ounce jar of honey at the supermarket. That represents “the efforts of tens of thousands of bees flying a total of 112,000 miles to forage nectar from about 4.5 million flowers,” writes Buchmann.
Of course, we primarily appreciate honey bees for their pollination services (one-third of the food we eat is pollinated by bees) but honey is more than just an after thought.
It's been described as “liquid gold,” “the nectar of the gods” and “the soul of a field of flowers.” Frankly, it's nothing short of miraculous.
And well it should be.
A honey bee sips honey from honeycomb. (Photo by Kathy Keatley Garvey)
A honey bee sips nectar from a lavender blossom. (Photo by Kathy Keatley Garvey)
This time of year, it can be hard to resist the pull of sweet potatoes — roasted, mashed with butter, and topped with a combination of delectable treats from maple syrup to pecans to marshmallows. But did you know that the green leaves of the sweet potato plant also have the potential to be a tasty, nutritious food?
In Ethiopia, where sweet potatoes can be a staple crop, UC Davis graduate student Lauren Howe recently helped farmers taste test the leaves and consider this familiar crop in a new culinary light.
Watch a video to learn how to prepare sweet potato leaves:
The leaves of this drought-tolerant plant offer farming households there an alternative — and nutritious — food in the lean season, while they are waiting for its starchy, tuberous roots to be ready to eat. Introducing sweet potato leaves as a food option is intended to help farmers better diversify their families' diets, to include a wider variety of vegetables in addition to staple foods, especially during the dry season.
Boots on the ground with sweet potato farmers in Ethiopia
Lauren traveled to Ethiopia this summer to work with an organization called Send A Cow Ethiopia (SACE), on a Trellis Fund project. As part of the Horticulture Innovation Lab, each Trellis Fund project connects an organization in a developing country with a grad student from a U.S. university, to work together to benefit local farmers, while building the capacity of both the local organization and the student.
In Ethiopia, SACE helped Lauren better understand local contexts by connecting her with farming households to interview about their current farming practices and the role of sweet potatoes in their diets.
Later they traveled to meet with a group of about 25 farmers in the Ukara community to harvest leaves, cook together and discuss their perceptions of the leaves as a vegetable option.
Reflecting on taste tests, new foods, and rural communities
Lauren's own passion for food and witnessing how food can help build community is an important part of her reflection on this experience:
"This project is about creating tasty dishes to persuade people about the nutritional benefits of a new ingredient. It is gathering families, friends and neighbors to sit down to a communal meal (already a strong Ethiopian practice), breaking bread together, sharing stories, experiences and hopes for the future."
Background and related international agricultural research
Lauren's experience with a Trellis Fund project in Ethiopia was supported by the Horticulture Innovation Lab, a research program led by Elizabeth Mitcham of the UC Davis Department of Plant Sciences, with funding from the U.S. Agency for International Development. With a focus on fruit and vegetable innovation, the Horticulture Innovation Lab seeks to empower smallholder farmers in developing countries to earn more income and better nourish their communities — as part of the U.S. government's global Feed the Future initiative.
Past research from the Horticulture Innovation Lab has focused on other leafy greens, specifically African indigenous vegetables, and also on sweet potatoes themselves (orange-fleshed sweet potatoes, that is). Though the program has not done in-depth research on sweet potato leaves for human consumption beyond this small Trellis Fund project, you can find more information about eating sweet potato leaves and tips in this bulletin from the University of Arkansas Cooperative Extension, and a wealth of information about sweet potato farming and gardening from the University of California Vegetable Research and Information Center.
Related Food Blog posts:
- New reason to give thanks for sweet potatoes
How orange-fleshed sweet potatoes are making a difference in some African countries
- More African indigenous vegetables on more plates
A brief look at some leafy greens popular in Eastern Africa
- Connecting with farmers over pineapple postharvest practices
Another Trellis student experience with a video
- ‘Local' farm inspiration from half a world away
A UC Cooperative Extension specialist reflects on his time as a Trellis student
Sweet potato leaves in Ethiopia - Horticulture Innovation Lab photo by Lauren Howe/UC Davis
Food Tank is hosting its inaugural summit, titled “Growing the Food Movement,” on Nov. 14 in San Diego at the Illumina Theater. The event is co-sponsored by the Berry Good Food Foundation, the University of California's Division of Agriculture and Natural Resources, and the San Diego Bay Food and Wine Festival.
More than 30 speakers and panelists from the food and agriculture world in the San Diego area and around the globe, including David Bronner, Ryland Engelhart, Jessica Greendeer, ANR's own Rachel Surls, UC Cooperative Extension sustainable food systems advisor in Los Angeles County, and Gabriele Youtsey, chief innovation officer, and many more are participating. Journalists Kirk Siegler from NPR and Mari Payton of NBC 7 will moderate the panel discussions between these diverse and engaging food leaders.
“Food is the ultimate bonding experience,” said Youtsey, “Cook a meal at home with your family and sit down to eat it together.”
“One of the nation's largest concentrations of people are in Southern California, yet it's often left out of critical conversations about the food system,” said Rose Hayden-Smith, who worked behind the scenes to persuade Food Tank to hold a summit in Southern California.
"San Diego County has 6,687 farms, more than any other county in the United State,” said Hayden-Smith, a UC Cooperative Extension advisor for youth, family and community development and editor of UC Food Observer. “Although 68 percent of those farms are 9 acres or less, the county's farmers rank number one in both California and the nation in production value of nursery, floriculture and avocados.”
The varied topography and microclimates allow San Diego farmers to grow more than 200 different agricultural commodities from strawberries along the coast, to apples in the mountain areas, to palm trees in the desert.
website and Facebook page and engage in the discussions on social media using #FoodTank. Hayden-Smith will be live-tweeting from the event for UC Food Observer.
After the event, all videos will be immediately archived on Food Tank's YouTube Channel. Some content will also be shared through the podcast “Food Talk with Dani Nierenberg.”
Here is a preview of the all-star speaker line up at the 2018 San Diego Summit to advance the conversation about growing the food movement.
Alina Zolotareva is the Senior Marketing Manager and Product Champion at AeroFarms, the largest indoor vertical farm in the world, growing local, nutrient-dense, responsible leafy greens year-round. A natural communicator, connector, and problem-solver, Alina is passionate about driving transformational change and innovation in the realms of food, nutrition, public health, and urbanization as a registered dietitian nutritionist, marketer, and product developer.
Candice Woo is the founding editor of Eater San Diego, a leading source for news about San Diego's restaurant and bar scene. Keep up with the latest Eater San Diego content via Facebook or Twitter, and sign up for Eater San Diego's newsletter here.
David Bronner is the Cosmic Engagement Officer (CEO) of Dr. Bronner's, the top-selling brand of natural soaps in North America and producer of a range of organic body care and food products. He is the grandson of the company's founder, Emanuel Bronner, and a fifth-generation soapmaker. David is an activist, philanthropist, and ardent supporter of fair trade, animal rights, drug policy reform, and regenerative organic agriculture among other issues.
Evelyn Rangel-Medina is Chief of Staff for Restaurant Opportunities Centers (ROC) United, whose mission is to improve wages and working conditions for the nation's low wage restaurant workforce. An experienced manager, public interest lawyer, public policy advocate, and campaign director, she has worked with a broad range of nonprofit organizations to advance lasting social change. At ROC-United, she manages two worker centers that organize hundreds of immigrant low-wage workers of color to advocate for higher labor standards and dignified working conditions.
is the Chief Innovation Officer at University of California, Agriculture and Natural Resources (UC ANR), providing leadership to UC ANR's information technology unit to support programmatic, educational, administrative, and marketing-oriented projects. He has been active for many years in EDUCAUSE and Internet2 and speaks regularly on cloud computing, big data, collaboration technologies, the role of technology in academia, and cyber-security.
Heather Lake of Fox 5 San Diego has covered some of the city's largest events including Comic-Con and opening day at the Del Mar Races. Before heading to the West Coast, Heather was an anchor, reporter, and bureau chief at WCTI in Jacksonville, North Carolina, working closely with the military community at Camp Lejeune. Many of her most memorable assignments include working alongside Hope for The Warriors as the nonprofit granted “warrior wishes” to many of our service men and women.
Jeff “Trip” Tripician joined Niman Ranch in 2006 and has grown the brand to a national industry leader by expanding distribution channels and geographies as General Manager. Under his direction, the company has more than tripled in size while maintaining its core values and mission of raising livestock traditionally, humanely, and sustainably. He is passionate about helping the family farmer thrive in rural communities.
Jennifer Burney is an Associate Professor at the School of Global Policy & Strategy at UC San Diego. As an environmental scientist, her research focuses on simultaneously achieving global food security and mitigating climate change. She designs, implements, and evaluates technologies for poverty alleviation and agricultural adaptation, and studies the links between “energy poverty”—the lack of access to modern energy services—and food or nutrition security, the mechanisms by which energy services can help alleviate poverty, the environmental impacts of food production and consumption, and climate impacts on agriculture.
Jenny Ramirez is the Human Resources Director for California Harvesters Inc., an employee trust farm labor company in Bakersfield, California. Early in her business career she identified that the best way she could support workers was to be directly involved with setting policies and procedures, a role that she is reinventing at California Harvesters. Bringing over a decade of experience in California agriculture, she is passionate about using her position and training to improve working conditions for farm workers.
Jessika Greendeer is the founder of Waxopini Wiiwamasja, which is Ho-Chunk for “nourishing spirits.” She is responsible for stewarding Indigenous seeds, teaching others how to grow and preserve Ancestral foods, protecting her traditional foods and carrying out her vision of feeding her people. Jessika is a US Army veteran, who completed a Veteran-to-Farmer training program in Pennsylvania with Delaware Valley University and the Rodale Institute. She has brought her knowledge of organic farming back to her community by growing out ancestral landrace varieties and market vegetables within the Ho-Chunk Nation community gardens, working to heal and regenerate the earth throughout her ancestral homeland of Southern Wisconsin.
Josh Henretig is a Senior Director for Microsoft and is responsible for leading the Artificial Intelligence for Earth and Corporate Sustainability programs for the company. Over the years, Josh has contributed to all aspects of Microsoft's environmental strategy, from implementing responsible business practices that have led to the company's commitment to become carbon neutral and to be powered by 100% renewable energy through an internal price on carbon, to projects and programs that advance social opportunity and environmental sustainability in the communities.
Karen Archipley owns and operates a USDA certified HydroOrganic farming enterprise, headquartered in Escondido, California.The Archipley's founded Archi's Acres, Inc. in 2006 with two core objectives: to create a viable, sustainable, organic-produce farming business and develop a business that would provide entrepreneur opportunities for veterans in sustainable organic agriculture, bringing to light the many issues that veterans face when they leave the military and choose farming as a career.
Keith Maddox is the Executive Secretary Treasurer at the San Diego and Imperial Counties Labor Council and the 134 unions it brings together. The San Diego and Imperial Counties Labor Council is the local central body affiliate of the AFL-CIO, founded in 1891. The Labor Council offers an avenue for local unions to come together as a unified group, with a membership of more than 250,000 local working families.
Kirk Siegler of National Public Radio (NPR) covers the urban-rural divide in America, exploring the intersection between urban and rural life, culture, and politics. Based at NPR West's studios in Culver City, CA, but frequently roaming the country, Kirk's reporting has also focused on the far-reaching economic impacts of the drought in the West while explaining the broader, national significance to many of the region's complex and bitter disputes around land use. His assignments have brought listeners to the heart of anti-government standoffs in Oregon and Nevada, including a rare interview with recalcitrant rancher Cliven Bundy in 2014.
Lorena Gonzalez Fletcher is Assemblywoman for District 80, California State Assembly, elected in May of 2013 to fight for California's working and middle classes. In 2015, The Atlantic Magazine labeled her “The California Democrat setting the National Agenda” for her practical, progressive legislation aimed at alleviating real issues in people's lives. Lorena is the first Latina in California history to chair the Assembly Appropriations Committee. She is also Chairwoman of the Select Committee on Women in the Workplace and Vice Chair of the Latino Caucus.
Maria Hesse is the Managing Editor for Edible San Diego, a food and lifestyle designer, pug photographer at PugsMutt.com, and co-author of The Intentionalist Cooks! You can find her at MariaHesse.life or get in touch at firstname.lastname@example.org.
Mannah Gbeh owns and runs Bee Valley Farm. He is skilled in horticulture and agriculture, seasoned in public education and tours, and passionate about eradicating hunger in the world. As a young boy growing up in Liberia West Africa, agriculture was the way of life for Mannah. In 2007, he was Honorably Discharged from the United States Navy after serving seven years and doing three tours in the Middle East. In 2010, he started the Nursery Technology program at Cuyamaca College.
Mari Payton of NBC 7 is a senior investigative reporter leading the award-winning NBC 7 I-Team. Mari's stories have prompted local, state, and federal investigations and caused law and policy changes. She's reported breaking news live on the TODAY show, MSNBC, and other NBC stations across the country. She's also received numerous awards from the Society of Professional Journalists and Press Club.
Michael Gardiner is a food writer for San Diego CityBeat and a licensed California attorney. In addition to San Diego CityBeat, he is the monthly food columnist for L'Chaim San Diego Magazine and the primary writer for the San Diego Food & Travel Blog, www.sdfoodtravel.com.
Michael Hamm is Senior Fellow at the Center for Regional Food Systems at Michigan State University. Michael founded the C.S. Mott Group for Sustainable Agriculture in 2003 and was founding director of the MSU Center for Regional Food Systems from 2011-2015. Michael is affiliated with the departments of community sustainability; plant, soil and microbial sciences; and food science and human nutrition. Community food security and community, regional, and sustainable food systems are research interest areas.
Michelle Lerach is a lawyer, entrepreneur, activist, and President of the Berry Good Food Foundation. In 2008, she received the Consumer Attorneys of California Women's Law Caucus Outstanding Consumer Advocate Award before leaving the practice to commit herself fully to social activism. An “agvocate” for sustainable food, she founded Berry Good Night and Berry Good Food Foundation to advance a healthy, integrated food system by educating, connecting, and supporting food producers and consumers. An outspoken critic of current GMO labeling policy, she serves on the steering committee of Californians for GE Labeling.
Michelle Parente is the Dining, Wine + Lifestyle reporter for The San Diego Union-Tribune. Her areas of expertise include the Valle de Guadalupe wine region, fashion, television, women's issues, and coverage of aging, such as the impact of Alzheimer's and dementia and family caregiving. A native New Yorker, Michelle received her B.A. in political science and Italian Literature at UC Berkeley. In 1980, she studied at L'Università di Urbino, in Italy. One of her life's goals is to make her way through each of the world's great wine regions.
Nate Looney is an urban farmer, army veteran, entrepreneur, and owner of Westside Urban Gardens. Founded in 2015, Westside Urban Gardens is an urban agricultural startup, using controlled environment techniques to cultivate gourmet leafy greens and microgreens. These crops are Homegrown By Heroes. A graduate of the Veterans to Farmers Controlled Environment Course, Nate also completed a Farmer Veteran Coalition internship, funded by The San Francisco Foundation at Ouroboros Aquaponic Farms in Half Moon Bay, CA.
Neil Nagata is the President of the San Diego County Farm Bureau and Nagata Bros Farms, a third generation Oceanside farmer with over 30 years' experience in fresh fruit, vegetable, and strawberry substrate/hydroponic production and research. He has worked with regulators and legislators to support fruit and vegetable production in the United States and internationally. As the founding president of the non-profit California Strawberry Growers Scholarship Fund, he has helped provide scholarships for children of California strawberry farm workers, raising over US $2 million.
Rachel Surls is the Sustainable Food Systems Advisor for University of California Cooperative Extension Los Angeles County. Involved in a variety of projects related to urban food systems, she has worked with UCLA students to conduct the “Cultivate LA” survey of urban agriculture in Los Angeles. She recently led a UC ANR team that carried out a statewide needs assessment of urban farming. Rachel and a co-author recently published a book on the local history of urban agriculture, titled From Cows to Concrete: The Rise and Fall of Farming in Los Angeles.
Ryland Engelhart is the Mission Fulfillment Officer and co-owner at Cafe Gratitude and Gracias Madre, as well as Co-Founder of Kiss the Ground, educating and advocating about the connection between soil, human, and planetary health. He is also a co-creator of the award-winning, transformational documentary film, “May I Be Frank.” He is an entrepreneur and activist, using his restaurants as a platform to inspire more gratitude in our culture. He speaks on sacred commerce, tools for building community, and regeneration.
Sarah Mesnick is an Ecologist, Southwest Fisheries Science Center, NOAA Fisheries, and Adjunct Professor, Scripps Institution of Oceanography, UC San Diego. Focused on social evolution in the ocean and on the role of social behavior in explaining patterns of species diversity, the main goal of her research in recent years is to provide a social framework within which to investigate stock identity, population trends, and fishery interactions in cetaceans. She serves as liaison between CMBC and NOAA SWFSC and leads the Sustainable Local Fisheries project.
Stepheni Norton is the owner of Dickinson Farms, a retired Chief Petty Officer and decorated military Veteran, with over 20 years of entrepreneurial experience. Stepheni's farming journey began after purchasing the Dickinson homestead, subsequently deploying and falling ill. After almost three years of misdiagnosis, she was properly diagnosed with stage 3 Lyme Disease, and promptly started daily IV treatment. Designing a farm layout and business plan from the IV chair, she successfully built the first and only licensed farm in National City—an heirloom fruit, vegetable, and herb farm. Norton contributes her free time to help aspiring and small business owners build and grow their businesses.
Vince Hall is the CEO of Feeding San Diego, with extensive nonprofit and public sector management experience, including serving as Staff Director for Governor Gray Davis. He also served as a lecturer at San Diego State University and his previous community involvement included serving on the San Diego Community College District Trustee Advisory Council, the San Diego Unified School District Citizen Bond Oversight Committee, and the boards of the National Conflict Resolution Center, San Diego Regional Technology Alliance, and the San Diego Diplomacy Council.
When it comes to watering walnuts, most California growers believe you need to start early to keep trees healthy and productive throughout the long, hot summer. But according to striking results from a long-term experiment in a walnut orchard in Red Bluff, growers can improve crop production if they hold off irrigation until later in the season and directly measure their trees' water needs.
The findings from researchers at the University of California may help farmers optimize water use.
“It's a game-changer,” said walnut grower Hal Crain, who welcomed researchers on to his orchard to test irrigation optimization. “It's clear to me you can improve nut quality and yield by applying water based on what the tree wants and needs, rather than just watering when it's hot outside and the soil is dry. That's a big deal for walnut growers and for the entire agricultural industry.”
Changing the paradigm
Crain is a second-generation farmer whose family has been growing walnuts in Butte and Tehama counties for 55 years. Like most walnut farmers, Crain had always started irrigating in early to mid-May when the days grew warmer and the trees sprouted leaves.
“That's standard practice for probably 90 percent of California's walnut growers,” said Crain, walking amid his trees on a sunny afternoon. “The theory is that when you irrigate early, you preserve the deep moisture in the soil that trees need to survive the heat of summer.”
But that's not how it works, the research shows. Instead, trees that grow in saturated soil early in the season don't develop the deep roots they need to thrive.
“With all the water right there at the surface, the lower roots suffer,” explained Bruce Lampinen, UC Cooperative Extension orchard management specialist with the UC Davis Department of Plant Sciences. “Trees end up with a very shallow root system, which doesn't serve them well as they try to extract moisture from the soil later on.”
Lampinen has long suspected that walnuts were getting too much water in the spring.
“A lot of the symptoms we see like yellowing leaves and various diseases can all be explained by overwatering,” said Lampinen.
So Lampinen did what scientists do: He set up an experiment. Five years ago, with funding from the California Walnut Board and the U.S. Department of Agriculture, he joined forces with Ken Shackel, a plant sciences professor with UC Davis, and Allan Fulton, an irrigation adviser with UC Cooperative Extension. Together, they led a team of scientists testing irrigation on Crain's ranch.
“Hal is an exceptional partner,” Fulton said. “Farmers have a lot to accommodate when they host an experiment like this, with researchers going in and out of the orchard at all hours. He had to work around our people and the timing of our water treatments. He's always eager to experiment with technology and learn new things, and he shares what he learns with other growers. Hal completes the circle.”
Tough nut to crack
When is the best time to irrigate? Researchers say the trees hold the answer. Scientists use pressure chambers, which are air-pressure devices that measure a leaf or small shoot to gauge how hard the plant is working to pull moisture from the soil.
“Just because the soil looks dry doesn't mean the plant is suffering,” said Shackel, who specializes in plant physiology. “Pressure chambers let you ask the tree how it's feeling — sort of like taking a human's blood pressure — which is a much more accurate way to measure a plant's water needs.”
For the last five years, the team has been applying different water treatments to five blocks of trees. One block is getting standard, early irrigation. Crain's orchard managers begin irrigating the other blocks when the trees reach different levels of water stress based on pressure-chamber readings.
The trees that experience moderate stress are doing the best. Their irrigation usually starts in mid-to-late June, several weeks later than when standard watering begins.
“You can tell just by looking at that block that the trees are healthier,” said Crain, standing beneath a canopy of lush, green trees. “And, we're starting to see greater yields and better nut quality.”
Translating the research
The research is helping scientists advise farmers on irrigation.
“My biggest take-away is knowing when to start watering is a really important factor to the health of your trees,” Lampinen says.
Pressure chambers — sometimes called pressure bombs — can cost more than $3,000, and high-tech versions are under development.
“I tell growers a pressure bomb would pay for itself even if you just used it once a year to determine when to start watering,” Lampinen said.
Crain is certainly convinced.
“When you irrigate based on your trees' needs, you optimize water,” Crain says. “I'm not using less water overall, but the water I do use is producing more food. That's good news for everyone.”
This story was originally published in the Fall 2018 issue of Outlook Magazine, the alumni magazine for the UC Davis College of Agricultural and Environmental Sciences.