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Biodigesters turn food into electricity, but can they also create fertilizer?

On a recent late-summer Wednesday, a freight container filled with cases of expired Muscle Milk protein drink awaited unloading at the UC Davis Renewable Energy Anaerobic Digester (READ) while a front-loader scooped heaps of spoiled vegetables into a mechanical processor. Nourished by a diet of assorted food waste from the UC Davis campus and area restaurants and markets, READ harnesses the activity of billions of microbes to produce biogas capable of generating 5.6 million kWh per year of clean electricity for UC Davis.

Out of date products are sent to the aenorobic biodigester to be converted to energy and now fertilizer

But a by-product of READ and other anaerobic digesters – the slurry of leftover solid and liquid material, or digestate – has caught the attention of UC Davis researchers interested in “closing the loop” on food production, consumption, and waste. When processed through an anaerobic digester, organic materials like food discards, expired or off-spec food products, or animal manure can be transformed into concentrated biofertilizers and soil amendments that are highly effective and easily applied to crops.

In an interdisciplinary collaboration at the Russell Ranch Sustainable Agriculture Facility, funded by the California State Water Resources Control Board and the California Department of Food and Agriculture, UC Davis faculty and students have developed a pilot-scale process for commercial production of several forms of this biofertilizer using digestate from READ and other nearby digesters. They are also evaluating their effects on yield and other agronomic metrics in corn and tomato field trials – paving the way for farmers and growers to take advantage of a highly sustainable source of plant nutrition.

The challenge and opportunity of fertilizer from anaerobic biodigesters

The digestate from READ and other digester facilities can be applied directly to soil as a fertilizer, but, because it has a limited shelf-life, it usually must be applied to land in the immediate region of the facility. With the input of food waste that can vary widely from day to day, a facility's digestate is inconsistent in texture and composition, making it difficult to transport and apply to fields using common farm fertilizer equipment.

Filtering and drying this digestate, however, results in solid and liquid forms that can be concentrated, homogenized, easily transported, and applied to soil through existing drip irrigation systems or surface spreading equipment.

This process could allow farmers and growers located further away, and working with common irrigation and fertilizer application equipment, to supplement or replace their synthetic fertilizer consumption with biofertilizers from food waste or animal manure.

How do biodigestate products measure up to synthetic fertilizers?

The research, co-led by professor Ruihong Zhang from the UC Davis Department of Biological and Agricultural Engineering (who also designed READ in partnership with Sacramento-based tech company CleanWorld) and Professor Kate Scow from the Department of Land, Air, and Water Resources, developed pilot-scale systems to efficiently and consistently separate the solid and liquid portions of food- and manure-based digestates. The researchers then examined the nutrient composition of the solid and liquid biofertilizer products, finding that biodigestate-based fertilizers contain valuable nutrients and microbes not found in many synthetic fertilizers.

In current field trials, the researchers are investigating the effects of each of the biofertilizer products on crop yield and quality. Their preliminary results show that it is possible to grow irrigated processing tomatoes and short-season corn using biofertilizer products as the sole source of fertilizer. The origin of the fertilizer matters, however – manure-based liquid fertilizer formed additional large particles after the final filtration, creating concerns about clogging the drip irrigation system. The team thinks an environmentally benign chemical sometimes added to manure digesters to clean the biogas may be the culprit of the problem, but future research is needed. The solid biofertilizer pellets they developed show much promise, as they can be applied using existing methods for spreading compost and can be economically transported farther away from the digester.

In addition to better understanding the best processes for producing and using the biofertilizers, further research is needed to understand how much of the nitrogen in each of the fertilizer products is available for uptake by the crop, as well as economic analyses to determine the commercial-scale production and transportation costs. The researchers will be able to narrow in on the agronomic and economic potential of biofertilizers through the upcoming analysis of the yield of the corn and tomato experiment plots at Russell Ranch. The results of a tomato experiment recently showed that the digestate fertilizers produced just as much fruit as a popular synthetic fertilizer.

UC Cooperative Extension advisor Gene Miyao looks at biofertilizer in its various stages, from raw waste to fertilizer

Interdisciplinary research for agricultural innovations

Russell Ranch, a program of the Agricultural Sustainability Institute, is designed as a shared space for interdisciplinary research and innovation. The biofertilizer research, among other active projects at Russell Ranch, is an example of the fulfillment of that intention. “The soil scientists are learning engineering, the engineers are learning biology, and the biologists are learning about soil,” Professor Zhang remarked.

The exchange also extends beyond the university: a recent UC Davis Biofertilizer Field Day drew attendees from the UC Division of Agriculture and Natural Resources, several public agencies, the agricultural sector, other universities, nonprofits, entrepreneurs, and food processors. If the research continues to illuminate a way forward for biofertilizers, these audiences may fill important roles in bringing this new technology into practice – and in recycling your lunch leftovers back into a more efficient and sustainable food system.

More information: UC Davis READ, Russell Ranch, and the biofertilizer research

The UC Davis Renewable Energy Anaerobic Digester was unveiled in 2014 as the nation's largest anaerobic biodigester on a college campus, and represented a unique private-public partnership. Professor Ruihong Zhang invented the anaerobic digestion technology used by CleanWorld, which developed it into one of the most advanced commercially-available digester systems in the country.

Russell Ranch Sustainable Agriculture Facility is a “living laboratory” for interdisciplinary field research and innovation. Its flagship project, the Century Experiment, measures the long-term impacts of energy, water, carbon, and nitrogen inputs on agricultural sustainability in the flagship Century Experiment.

The biofertilizer research collaboration includes Zhang Lab graduate students Tyler Barzee and Hossein Edalati, Scow Lab postdoctoral researcher Daoyuan Wang, and Russell Ranch manager Israel Herrera. Collaborating institutions include CleanWorld, California Bioenergy, New Hope Dairy (Galt, CA), Fiscalini Dairy (Modesto, CA), and Sacramento Municipal Utility District.

Posted on Thursday, September 15, 2016 at 8:30 AM

Tips for a successful fall vegetable garden

When planning a fall garden it is important to take into consideration the first frost dates in your area to protect your crop. (Photo: Melissa Womack)
For many gardeners' spring and summer months are synonymous with growing edible gardens, but home vegetable gardening doesn't have to end when cool fall temperatures arrive. This fall, take advantage of California's unique climate that makes it possible to grow a variety of crops throughout the year.

Warm vs. cool season crops

Most vegetables are classified as either a warm season or cool season crop. This designation is based on the temperature range that the plants thrive in. Warm season crops grow best when the days are long and the temperatures are high (between 65°-95°F). In contrast, cool season crops grow and produce the best quality produce when the average temperatures are between 55°-75°F and are typically tolerant of light frosts when mature.

Typical cool season crops include root vegetables such as: beets, carrots, parsnips, and radishes; stems such as asparagus and rhubarb; leafy crops like cabbage, celery, lettuce, spinach and crops that have edible immature flowers like artichokes, cauliflower, and broccoli.

Importance of frost dates

Scarecrows are a staple decoration in autumn but they also serve a purpose in the garden of scaring off unwanted birds and animals. (Photo: Melissa Womack)
According to the UC Master Gardener Program's gardening resource the California Garden Web it is important to keep in mind the first and last frost dates in your area and protect plants if frost is expected, unless the crop is frost tolerant and established enough to handle the weather.

“When deciding what to plant in your edible garden it is important to take into consideration the best months a crop will thrive,” says Missy Gable, statewide director for the UC Master Gardener Program. “Fall can be a very rewarding gardening season. There are a variety of delicious crops that can survive the cooler temps and have a short number of days to maturity.”

Guides for determining the first and last frost dates for a specific area or region are available using historical references from the National Weather Service. Visit the California Garden Web section When should plant my garden? Frost dates webpage for detailed information about when to safely plant frost-tender crops.

Cool season vegetable gardening at a glance: 

Learn more with the UC Master Gardener Program

Artichokes are a beautiful addition to the fall edible garden. For optimal flavor and tenderness artichokes should be harvested before leaves open. Pictured above is the striking purple bloom of an unharvested artichoke. (Photo: Melissa Womack)
Interested in learning more about how to grow a thriving edible garden or home landscape? The UC Master Gardener Program has University-trained volunteers who are eager to help. Volunteers are available to answer questions about preparing your soil, fertilizing, mulching and more. With local programs based in more than 50 counties across California there is sure to be a workshop or class near you. Visit our website to find your local UC Master Gardener Program,




Vegetable Gardening Basics,
California Gardening Web,
California Master Gardener Handbook, Home Vegetable Gardening, page 338-339,
University of California Cooperative Extension Vegetable Research & Information Center,

Posted on Tuesday, September 13, 2016 at 8:49 AM

More irrigation for climate-smart farming and food security in Guatemala

Connecting 9,000 rural households in Guatemala with improved water management and climate-smart agriculture strategies is the goal of a new project led by a team at UC Davis, to ultimately increase food security and reduce poverty in Guatemala's Western Highlands.

Meagan Terry, left, a UC Davis researcher with the Horticulture Innovation Lab in Guatemala, discusses conservation agriculture with a Guatemalan consultant and a local youth group member. (Photo by Beth Mitcham)
Called MásRiego (“more irrigation”), the project aims to increase farmers' incomes and their use of climate-smart strategies, including drip irrigation, rainwater harvesting, reduced tillage, mulch use and diverse crop rotation. To enable farmers to adopt these new practices, the team will not only provide trainings but also build partnerships to increase farmers' access to needed micro-credit financing and irrigation equipment.

“The opportunity to impact so many farmers' lives on this scale is exciting,” said Beth Mitcham, director of the Horticulture Innovation Lab and a UC Cooperative Extension specialist in the UC Davis Department of Plant Sciences. “We're taking lessons learned from our previous research — in Guatemala, Honduras and Cambodia — and building a team to help more small-scale farmers apply our findings and successfully use these innovative practices.”

The new project is part of the U.S. government's global hunger and food security initiative, Feed the Future. The project represents an additional $3.4 million investment in the UC Davis-led Horticulture Innovation Lab by the U.S. Agency for International Development's mission in Guatemala.

The project's international team also includes representatives from Kansas State University; North Carolina Agricultural and Technical State University; the Centro de Paz Bárbara Ford in Guatemala; Universidad Rafael Landívar in Guatemala; and the Panamerican Agricultural School, Zamorano, in Honduras.

“The learning shared between these three U.S. universities and the universities in Honduras and Guatemala will be enriching for all of the institutions involved,” said Manuel Reyes, research professor at Kansas State University who is part of the team. “I find it satisfying that these academic institutions will be investing intellectually in marginalized groups in Guatemala's Western Highlands — and in turn, learning from them too.”

Helping youth envision a future in agriculture

Miguel Isaias Sanchez has started farming with drip irrigation and a water tower, using information from one of the first MásRiego trainings. (Photo by Beth Mitcham)
The new MásRiego project will focus on helping farmers, particularly women and youth, grow high-value crops on very small plots of land (200 square meters minimum), in the Quiché, Quetzaltenango and Totonicapán departments of Guatemala's Western Highlands.

By partnering with local youth groups and agricultural schools, the team will better prepare students for jobs in commercial agriculture and agricultural extension with knowledge of climate-resilient conservation and water management practices.

“Our local team is training youth as entrepreneurs, to see agriculture as an economic opportunity instead of just back-breaking work,” said Meagan Terry, UC Davis junior specialist who is managing the project in Guatemala for the Horticulture Innovation Lab. “They can envision a future in agriculture, with innovative ways to create value-added products or grow high-value crops for niche markets.”

As rainfall patterns vary with climate change, farmers in this region are expected to face increased competition for water. Practices such as rainwater harvesting, drip irrigation and conservation agriculture will become more necessary for small-scale farmers.

Climate-smart lessons from conservation agriculture, drip irrigation

In previous research, the Horticulture Innovation Lab has found that combining drip irrigation with conservation agriculture practices can successfully grow vegetables on small plots of land, without significant yield reductions. These practices improve soil structure, moisture retention and soil health.

Additionally, women farmers who participated in the Horticulture Innovation Lab studies in Cambodia, Honduras and Guatemala favored using these practices for another important reason: reduced labor in relation to controlling weeds, vegetable bed preparation and manual watering.

“I dream for many women, youth and their families, that their lives will be better off because of 'MasRiego' and the science behind this work,” Reyes said. “As for the research, we are learning how to improve this suite of practices so they can be tailor fitted globally. I am convinced that if this picks up, steep sloping lands can be farmed with the soil quality not being degraded — but even being enriched.”

These lessons, as well as findings from the program's “Advancing Horticulture” report about horticultural sector growth in Central America, lay the foundation for this new project.

A previous version of this article was published by UC Davis News Service and on the Horticulture Innovation Lab blog

Curious about partnering with the Horticulture Innovation Lab? The Horticulture Innovation Lab builds partnerships between agricultural researchers in the United States and researchers in developing countries, to conduct fruit and vegetable research that improves livelihoods in developing countries. The program currently has three research grant opportunities for U.S. researchers: one focused on tomatoes, another on apricots, and a third on integrated crop-livestock systems. 

Posted on Tuesday, August 30, 2016 at 8:02 AM

Mark your calendar for World Food Day events

The day for collectively taking action against global hunger is still two months away. But September and October are already shaping up as “world food months,” with a number of events connecting Californians to their food systems and the world's food challenges.

World Food Day officially falls on October 16, honoring the establishment of the United Nations Food and Agriculture Organization (FAO). In the meantime, here are a few worldly UC events to look out for, both online and in person:

UC Student Video Challenge calls for student stories

The World Food Center at UC Davis is kick-starting the World Food Day spirit of building awareness around solutions for ending hunger. In partnership with the UC ANR Nutrition Policy Institute and the UC Global Food Initiative, the Center launched a video contest for students across the 10 UC campuses—including extension offices and health systems—to capture stories on UC research related to food or nutrition security, as defined in the second of the UN's Sustainable Development Goals. Students can win up to $1,000 and a paid trip to the World Food Prize International Symposium. The deadline is September 7. 


World Bank and International Year of Pulses 

Combining World Food Day with the FAO's celebration of pulses for being a sustainable protein source, the agriculture and SecureNutrition groups at the World Bank are teaming up with the World Food Center to host a talk on the role of legumes in nutrition, climate-smart agriculture and serving low-income countries. Douglas Cook, director of the Chickpea Innovation Lab at UC Davis, will deliver the presentation, which will be streamed online as well, on October 6.

Talk from recent head of UN World Food Programme 

Speaking on the need for ensuring the world's neediest receive not only enough food, but the right food, World Prize laureate Catherine Bertini will deliver a public lecture in honor of World Food Day. The World Food Center is hosting Bertini at UC Davis on October 10, also with livestreaming available. The winning submissions for the World Food Day Video Challenge will be showcased ahead of the lecture.

barr kiko
(Photo: Karin Higgins/UC Davis)

UC research at World Food Prize 

Known as the “Borlaug Dialogue,” the World Food Prize International Symposium is the most prestigious gathering in food and agriculture. Beth Mitcham, head of the Horticulture Innovation Lab at UC Davis will speak at the symposium, while the World Food Center is again organizing a panel discussion, this time focused on measures of progress for nutrition security and featuring leaders from the FAO, the US Agency for International Development and the International Food Policy Research Institute.

In past years, World Food Prize laureates have included researchers from UC San Francisco, UC Berkeley and UC Davis. The symposium is held in Des Moines, Iowa, on October 12-14, and will be livestreamed as well.  

From “Tank” to “Fork” and everything in between 

While not directly connected to World Food Day, Sacramento's annual Farm-to-Fork celebrations have locals tipping their glasses to the close connection Californians share with the nation's top ag economy. Tastings, farm tours, food drives and street festivals span the month of September. The Farm Tank conference, meanwhile, is partnering with UC Davis and the Farm-to-Fork organizers to expand the foodie dialogue with a list of speakers ranging from corporate chefs to food reporters and UC ANR's chief information officer, Gabe Youtsey. The event also takes place in Sacramento, on September 22.

Posted on Monday, August 15, 2016 at 2:14 PM
  • Author: Brad Hooker

Summer farm fun

This time of year, most farmers don't get much sleep. Tomatoes, pears and peaches often ripen in the Sacramento Valley faster than the harvest crews can pick them, even working 12-hour days. But this is also the season that some farmers are happy to show off their farms to visitors, inviting guests to enjoy the delightful flavors and beauty of the harvest in a pause from the bustle. UC Cooperative Extension hosts an online agritourism directory and calendar,, to help Californians find farms and ranches to visit. Here are a few upcoming opportunities for summer fun on California farms, pulled from the calendar:

  • The farmers of Five Foot Farm.
    Plumas County Farm Crawl
    - Up the Feather River Canyon, on the eastern side of the Sierras, are the beautiful communities of Quincy and Indian Falls. Small-scale growers, members of Plumas Grown, offer tours and fresh snacks from their fields from 8 a.m. to 12 p.m. on Saturday August 6, 2016. Each farm will offer tours on the half hour (8:30, 9:30, 10;30 and 11:30). Participating farms include a school garden project, Five Foot Farm, Shoofly Farm and Sundberg Growers. Strawberries, tomatoes, garlic, carrots, huge heads of lettuce, hoop houses, and intense cultivation on small plots will be featured. Bring the kiddos, friends and family (no dogs please). All of these operations use sustainable growing practices and are happy to chat with you about why they love to grow good food. Admission by donation, no pre-registration required. Learn more: (707) 217-6415 or
  • Good Humus Peach Party (Yolo County) - Every year on the first Saturday in August, Jeff and Annie Main, owners of 20-acre Good Humus Produce, hold a celebration to give thanks for the year's fruit harvest. They invite you all to come out, see the farm, have a refreshment and enjoy all that Good Humus has to offer. This is a pot luck party; guests are asked to bring a dish to share and their own plates, silverware and cups. No cost, but donations are welcomed. The Mains will provide peach pies, peach ice cream, peach salsa, peach pizzas, and more. You are invited to come early and be part of the experience of making all the peachy fun food. Other activities include a treasure hunt, farm tours, stock tank dipping, music and neighborly chat. Saturday August 6, 1 p.m. - 11 p.m. Learn more
  • Tomato Sauce Party at Eatwell Farm (Solano County) - It's time to join in on the tradition. Let's get canning! Tomato season is in full swing on the farm, and the plants are bursting with ripe and juicy tomatoes ready for picking. Join us as we harvest the bounty of the farm, toss it in a pot, and create delicious tomato sauce to savor the rest of the year. The produce is free, so bring as many jars as you can process over the two day event. The ticket price covers the cost of hosting the event and paying staff. Cost: adults $20, Children $5. August 6 - 7, 2016  Learn more and buy tickets here
  • Grape Days of Summer (Placer County) - Celebrate PlacerGROWN — local wine, local food, local agriculture. Take a self-guided tour of up to 20 wineries, taste foothill wines and enjoy a unique and educational experience at each stop on the Placer County Wine Trail. Saturday & Sunday, August 6 & 7, 11 a.m. to 5 p.m. WHERE: Placer County Wine Trail - Auburn, Lincoln, Loomis, Meadow Vista, Newcastle & Rocklin. Activities: Learn About Wine & Wine Making • Live Music at Some Locations • Food at Every Winery • Barrel Tastings • Vineyard Tours • Vertical Tastings • . . . and more! Tickets: Weekend Pass - $45.00,  Sunday Only - $25.00/person, Designated Driver - $10.00/person  website, more info
  • Wine and Produce Passport Weekend (Sacramento River Delta) - Just minutes from Sacramento and Elk Grove, along scenic CA Hwy 160, Delta Farm and Winery Trail members will open their farms and wineries to the public. Farms are open from 9:00 a.m. to 5:00 p.m. and wineries from 11:00 a.m. to 5:00 p.m.  During Passport Weekend, enjoy farm tours, local wine tastings, farm equipment displays, and contests. Fresh produce - including tomatoes, pears, melons, squash, stone fruits, sweet corn, zucchini, beans, eggs, and organic produce - will be readily available at many of the farms. Saturday and Sunday August 13 and 14. Tickets: adults $25 in advance, $35 week of purchase and are valid for both days. Kids under 21 are free. Tickets are available for purchase online at Each visitor over 21 will receive a wine glass at their first winery stop.
  • Good Land Organics Coffee Tour (Santa Barbara County) - The tour will be lead by Good Land Organics owner and grower, Jay Ruskey. You will be welcomed with fresh coffee, freshly made juice and seasonal fruit.  Jay will give an overview of the coffee research collaboration that has been conducted with the assistance of the University of California Small Farm Program.  He will then lead you on a moderate level hike where Ruskey will explain the dynamics of new crop adaptation and integration of organic tree fruit agriculture. The walk will
    Coffee trees at the Good Land Organics farm.
    take you through the eclectic mix of exotic fruit varieties that grow on the farm. Each person will have an opportunity to taste a fresh picked coffee berry and discover the original flavors of the coffee bean, while discussing coffee cultivation and post harvest processing. On your return hike, there will be time for open discussion and for any further questions.  At noon you have the option to enjoy your picnic lunch at our pond. August 13, 2016, 10:00 a.m. - 1:00 p.m. Cost: $50 per person. website, reservations

Learn about more farms, ranches and adventurous fun at

Posted on Monday, August 1, 2016 at 2:12 PM

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