- Author: Jeannette Warnert
As a start, spread organic mulch on the top of soil to boost its quality over time. As the mulch breaks down, soilborne organisms slowly churn it back into the soil and eventually move it through the soil profile. Spread leaves, pine needles, small trimmings, grass clippings, wood chips or straw two- to four-inches deep on the surface and let the soil microorganisms to the work. The addition of water in the summer will help the mulch break down.
Step up your soil building game by adding plenty of compost. This is the technique UC Master Gardener Randy Thomson recommends in his Madera and Fresno county classes. Thomson joined the MG program in 2011 when he lived in Los Angeles County. Three years later became a Master Composter in Orange County. In 2018 he moved to Madera County and localized his teaching on traditional and worm composting.
“In urban areas, developers scrape off the topsoil and compact the dirt before building a home's foundation,” Thomson said. “How do you grow in that? We need to rebuild what was optimized for construction, garden in raised beds or grow plants in pots. In soil with organics, you can actually grow food.”
Thomson's interest in soil building began when, during his teen years, his foster mother took him to the family farm in Oregon's fertile Willamette Valley.
“I loved it. There's a logic to living with agriculture. Ag is a lot about listening and observing how to use an environment without destroying it,” he said. He has applied this concept to gardening, and prefers to “keep things simple.”
“Good soil is 50 percent air and water. Forty-five percent is sand, silt and clay. The last 5 percent is organic matter, more specifically, compost,” Thomson said.
This formula leads to a soil capable of supporting worms, bacteria, fungi, protozoa, nematodes and micro arthropods that eat each other, embody the nutrients and make them available for plants.
“Compost is all you need,” Thomson said. “If you take care of the soil, the plants will take care of themselves.”
Another benefit: with a little labor, compost is free. The inputs – plant trimmings, grass clippings, leaves and food scraps – are generated in and around the home. Follow Master Gardener composting instructions to transform them into a rich soil amendment.
![]() Collect food scraps. |
![]() Add food to the top of bin. |
![]() Add water. |
![]() Add shredded dry leaves. |
![]() Over time, contents compost. |
![]() Harvest from the bottom. |
The cold composting method doesn't require gardeners to regularly turn the pile, which can be labor intensive. |
Another Master Gardener, Tony Carrasco of Fresno County, uses compost, and has gardened successfully with the use of other organic fertilizers, such as steer manure, bone meal, blood meal, fish emulsion and worm castings.
“I use soil amendments because I saw it was working for farmers in the field,” he said. “I was always planting and experimenting. I noticed that this stuff works.”
When Carrasco was a child, he and his siblings worked in orchards, packing houses and fields when school was out of session. At age 17, he got a job installing air conditioning. “That's when I said, ‘No more field work for me.'” But he never lost his fascination with growing things.
After retirement, Carrasco became a Master Gardener. He is one of three managers at the program's demonstration garden, Garden of the Sun. He adopted several garden plots at the MG garden and at the community garden in Kingsburg, plus he gardens at home.
“Twice a year I till in compost, horse and cow manures and organics I buy in bulk at a nursery near Sacramento,” he said. “I don't have a formula. I've gotten to where my vegetables come out pretty good.”
Carrasco experiments with worm composting and introducing fungi to breakdown organic materials in the soil. He said he has also tried bokashi composting, a Japanese composting method that ferments food waste in an anaerobic environment with effective microorganisms and bokashi bran. (Learn more from Bokashi Fermentation by Dr. Michael Vincent Rodriguez, UC Merced on YouTube.)
Carrasco's gardens produce a bounty of beautiful produce, much more than his family can use. He donates the excess to friends, neighbors and the Kingsburg Senior Center.
“Of course, there is a cost. But for me, the return is the joy of gardening. It's a joy to share,” he said.
For more information about composting, download a two-page in a printable pdf format here.
/table>- Author: Jeannette Warnert
The summer months in Fresno County are ideal for garden soil solarization, an environmentally sound way to kill weeds, insect pests and soil pathogens with free and naturally abundant solar energy. No pesticides are used in the process.
The greenhouse effect of the sun's rays on clear plastic can heat up the top 12 to 18 inches of the soil to as high as 145 degrees under perfect conditions. Excellent pest control can be achieved by maintaining the soil at 110 to 125 degrees in the top 6 inches, according to the UC Integrated Pest Management Program. The hot soil environment will kill such pests as nematodes, grubs, cutworms, beetles and snail eggs. Disease pathogens, such as fungi that cause verticillium and fusarium wilt, die.
There are downsides. Solarization requires taking garden space out of production during the growing season for 4 to 6 weeks, but future garden success is likely worth the sacrifice. The process may also kill some beneficial soil organisms, though UC IPM reports that many beneficials survive solarization or quickly recolonize the soil afterward. Earthworms, often present in healthy soil, burrow deeper to escape the heat and return when the treatment ends.
To solarize soil, smooth an area and water uniformly to 12 inches deep, then cover it with clear plastic. Rolls of clear plastic “drop cloth” are available in the paint sections of large home stores and online. Thin plastic (1 millimeter) provides greater heating but is susceptible to tearing; slightly thicker plastic (1.5 to 2 millimeters) is better for windy areas. Secure the plastic tightly over the soil with shovelfuls of soil, lumber, rocks, landscape staples or anything that will keep the breeze from catching the edges. Leave the area undisturbed for 4 to 6 weeks or longer in cooler temperatures or if the area is shaded part of the day.
After solarization, the bed can be planted immediately with seeds or transplants.
Fresno County Master Gardener Emily LaRue is solarizing a garden bed at the program's demonstration garden, 1750 N. Winery Ave., Fresno. The Garden of the Sun is open to public visitors from 9 to 11 a.m. Mondays, Wednesdays and Fridays.
For more information on soil solarization, see the UC IPM Pest Note: Soil Solarization for Gardens & Landscapes.
- Author: Lauren Fordyce
While preparing your garden for planting this spring, you may have found white grubs in the soil. Discovering these fairly large, white grubs can be alarming, but they usually won't cause significant plant damage.
Grubs are the soil-dwelling larvae of beetles in the Scarabaeidae family, also simply called scarabs. They are generally curled in a C-shape with whitish bodies and 6 legs. Grubs of some species may be less than 0.5 inch long, while other species may be up to 2 inches. Some grubs feed on living plant material while others do not.
Masked chafer beetle grubs are often what people find in garden beds in California. If you find large grubs in compost, those are likely the larvae of the green fruit beetle (also commonly called figeater beetle and green fig beetle). Japanese beetles are not usually present in California, but there are a few small hot spots under eradication efforts by the California Department of Food and Agriculture.
In most cases, the presence of grubs does not require pesticide treatment and populations of 6 or less per square foot won't cause significant damage. If you notice them in your garden beds, they can be hand-picked and killed. Some may choose to feed them to their backyard chickens or leave them out for wild birds. Beneficial nematodes can be applied to control grub infestations.
To learn more about common white grubs, visit https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=56797
- Author: Ben Faber
Soil Biodiversity in California Agriculture: Framework
and Indicators for Soil Health Assessment
Prepared by: California Department of Food and Agriculture Below Ground Biodiversity Advisory Committee
Soil health depends on soil biodiversity.
However, external pressures from land-use change, climate change and certain agricultural practices threaten the biotic networks that underpin the delivery of soil's many ecosystem services. Yet measuring soil biodiversity is a complex task, with a wide variety of possible indicators, and methodologies that are evolving with recent technological advances. This report, prepared by the Belowground Biodiversity Advisory Committee (BBAC) convened by the California Department of Food and Agriculture (CDFA), focuses on how best to assess soil biodiversity in the context of working lands and considers current and future challenges faced by California agricultural producers, policy makers, governing agencies, and related stakeholders. The report presents information on the taxonomic and functional diversity of soil organisms, ecosystem services they provide, threats to soil biodiversity, assessment frameworks, and biodiversity indicators. Examples of how biodiversity indicators can be applied to specific use cases provide insights for soil health, sustainable and climate-smart agriculture, and biodiversity conservation in California.
Soil biodiversity is the interconnected ‘social' network of numerous species of living organisms that contribute to soil functioning. As these organisms grow, die, and interact with soil's abiotic components, they perform essential functions in carbon, water and nutrient cycling and plant growth, collectively described as multifunctionality, benefiting ecosystems and humans alike. Comprehensive assessment of soil biodiversity involves measurements of organism abundance, identity, and functional diversity or traits, ideally in tandem with measurements of soil processes, as well as interactions among organisms. Soil biodiversity and soil processes vary in space and time due to factors like location, climate, vegetation, and land management practices across California's diverse landscapes.
Soils are incredibly biodiverse habitats, containing a vast array of organisms ranging from macroscopic organisms like gophers to microscopic worms, fungi, and billions of bacterial cells. The physical and chemical properties of soils – soil texture, pH, water and oxygen content, salinity, organic matter inputs, and nutrients – determine the types of organisms found in a particular habitat. The array of organisms inhabiting soil spans over six orders of magnitude in size, and includes microorganisms (viruses, bacteria, archaea, and fungi); microfauna (protists, nematodes, and tardigrades); mesofauna (mites and springtails); and macrofauna (earthworms). Life in soil exists in ecological communities that are complex and interconnected. These interconnections provide stability to soil functions. Soil organisms are critical to regulation of greenhouse gases, both by consuming and producing gases such as nitrous oxide, carbon dioxide, and methane. Mycorrhizal fungi in symbiosis with most plant species promotes root growth and availability of water and nutrients. A broad range of soil organisms mediate the decomposition of organic inputs and enhance nutrient cycling. Other functions of biodiverse soils include soil structure formation, organic matter formation, carbon storage, water regulation, and pathogen suppression. But despite these critically important functions, the diversity and complexity of soil biodiversity makes it challenging to decipher these intricate relationships and understand the impact of human activities.
Soil biodiversity faces many of the major threats from human activities and global change that also impact soil health and sustainability of California's agroecosystems. Land use changes, intensive agriculture, climate change, pollution, invasive species, overexploitation, and loss of habitat connectivity all pose risks. These threats disrupt soil biological networks, reduce biodiversity, impair ecosystem functions, and degrade soil structure and fertility. Soil biodiversity loss reduces multifunctionality and the provision of ecosystem services, highlighting the need to recognize the value of belowground communities to overcome challenges such as climate change, land degradation, and overall biodiversity loss. Addressing these challenges through sustainable land management, agroecological approaches, and awareness campaigns is crucial for preserving belowground biodiversity to maintain provision of essential ecosystem services.
READ ALL ABOUT SOIL DIVERSITY in the Report:
https://www.cdfa.ca.gov/oefi/biodiversity/docs/Soil_Biodiversity_California_Ag_July_2023.pdf
![soil food web image soil food web image](/blogs/blogcore/blogfiles/105737.jpg)
- Author: Michael Hsu
Anaerobic soil disinfestation helps suppress weeds, disease without fumigants
Troubled by puny plants, low yields and persistent mite problems, third-generation Southern California strawberry grower Glen Hasegawa was ready to give up on his transition from conventional to organic 12 years ago.
“I've always liked a challenge – but it turned out to be more of a challenge than I thought it would be!” he said.
But then, with the help of scientists including Oleg Daugovish, UC Cooperative Extension strawberry and vegetable crop advisor in Ventura County, Hasegawa tried a technique called anaerobic soil disinfestation (ASD). When applied correctly, the multi-step ASD process creates a soil environment that suppresses pathogens and weeds and makes for healthier, more robust crop growth.
“Back in the day, it was really hard to get the plant growing vigorously in organic,” said Hasegawa, owner of Faria Farms in Oxnard. “So we started using the ASD and then you could definitely see that the plant had more vigor and you could grow a bigger, better plant using it.”
Seeing that he could produce yields “in the neighborhood” of those grown in conventional strawberry fields fumigated with synthetic fumigants, Hasegawa was able to expand his original 10 acres of organic strawberries to 50 acres.
“I guess you could say I'm kind of a convert,” he said, noting that he now applies ASD to all his acreage each year in late spring.
Joji Muramoto, UC Cooperative Extension specialist in organic production based at UC Santa Cruz, has been experimenting with ASD since it was first brought to the U.S. from the Netherlands and Japan in the early 2000s. Carol Shennan, a professor in the Department of Environmental Studies at UCSC, and Muramoto were among the first to try the technique in California. They found that ASD successfully controlled an outbreak of Verticillium wilt – caused by the pathogen Verticillium dahliae – at UCSC's small organic farm in 2002.
Since then, Shennan, Muramoto, Daugovish and their colleagues have seen encouraging results at 10 trial sites across the state.
“We demonstrated that ASD can provide comparable yields with fumigants, in side-by-side replicated trials,” Muramoto said.
ASD promotes host of beneficial changes to soil ecosystem
ASD comprises three basic steps: incorporating a carbon source that is easily digestible by microbes in the soil (traditionally, rice bran has been used), further encouraging fermentation by covering the soil with plastic to limit oxygen supply, and finally adding water through drip irrigation to initiate the “anaerobic” decomposition of the carbon source and maintain the three-week “cooking” process.
The resulting cascade of chemical, microbiological and physical changes to the soil creates an ecosystem that is both conducive to strawberry growth – and inhospitable to pathogens and weeds.
“It's not like a pesticide where you have a mode of action, and thus resulting in ‘A' and ‘B' for you,” Daugovish explained. “There's a sort of cocktail of events that happens in the soil; they all happen interconnectedly.”
Compared to similar fields that did not undergo the process, ASD-applied organic strawberry fields across California have seen yields increase by 60% to 70% – and even doubling in some cases, according to Daugovish.
The UCCE advisor also shared the story of a longtime grower in Ventura County, who came to him with fields in “miserable” condition; they were plagued by one of the world's worst weeds, yellow nutsedge, and infected with charcoal rot, a disease caused by the fungus Macrophomina phaseolina. But after applying rice bran and following the ASD recipe, the grower saw phenomenal results.
“The only complaint he said to me was, ‘Now I have too many berries – we have to have more pickers to pick the berries!'” Daugovish recalled.
Via researchers' meetings, online resources, on-farm demonstration trials and word of mouth from peers, use of ASD by California strawberry growers has grown significantly during the past two decades. Tracking the purchase of rice bran, Muramoto estimated that about 2,500 acres were treated by the ASD-related practices in 2023 – covering roughly half of the 5,200 total acres of organic strawberries in California.
Muramoto directly links the growth of California organic strawberry production – which now comprises about 13% of total strawberry acreage in the state – with the increasing adoption of ASD.
“If you remove the acreage with the applied rice bran over the last 10 years or so, organic strawberry acreage is just flat,” he said.
Within the last decade, acreage of organic strawberries with ASD-related practices increased by 1,640 acres, which is a boon for air quality, human health and long-term soil vitality. According to Muramoto's calculations, that increase in organic acreage translates to a reduction of about 465,000 pounds of fumigant active ingredients that would have been used in growing conventional strawberries.
“There are hundreds of reports of acute illnesses related to fumigation in the record, so it's very important to find alternatives to fumigants,” said Muramoto, citing California Department of Pesticide Regulation documents.
Research continues to make ASD more economical, effective
The popularity of ASD has come at a price, however, for organic strawberry growers.
“There's more organic out there, and I think most of the organic guys are using it, so there's more demand on the rice bran; the price has been steadily going up every year, like everything else,” said Hasegawa, adding that he has been trying to decrease the amount of carbon while maintaining ASD's efficacy.
On top of greater demand from other growers and from beef cattle and dairy producers (who use rice bran as feed), the price also has increased due to higher costs in transporting the material across the state from the Sacramento Valley. So Daugovish and his colleagues – including Peter Henry, a U.S. Department of Agriculture plant pathologist – have been searching for a cheaper alternative.
“We all want an inexpensive, locally available, reliable, easy to use and functional carbon source, which sounds like a big wish list,” Daugovish said.
Carbon sources such as bark, wood chips, or compost are ineffective, as the crucial ASD microorganisms are choosy about their food.
“Microbes are just like cows; you can't feed them straight wood; they get pretty angry,” Daugovish explained. “And if you feed them something with too much nitrogen, they can't digest it – they get the runs. Microbes are the same way – you have to have the right proportion of stuff so they feel comfortable doing what they're doing.”
In search of an ideal replacement, researchers tried and ruled out grass clippings, onion waste, glycerin and coffee grounds. Finally, they pivoted to a material with properties very similar to rice bran: wheat bran, in the form of wheat middlings (also called midds, a byproduct of flour milling) and dried distillers' grain (DDG, a byproduct of ethanol extraction).
After field experiments in Santa Paula, the UC and USDA researchers found that midds and DDG were just as effective at controlling soilborne pathogens and weeds as rice brain – but at 25% to 30% less cost. Their results were published last year in the journal Agronomy.
“Not surprisingly, the wheat bran has worked almost exactly the same as rice bran,” Daugovish said.
He and Muramoto are now conducting trials with wheat bran at commercial fields, and the initial results are promising. Daugovish said the grower at one site in Ventura County has seen a 90% reduction in Macrophomina phaseolina, the causal pathogen of charcoal rot, in the soil – and an 80% to 90% drop in yellow nutsedge germination. They are waiting for final yield numbers after the coming summer.
While ASD has been beneficial to organic productivity and soil health, both Daugovish and Muramoto acknowledged specific limitations in suppressing the “big three” strawberry diseases: Verticillium wilt, Fusarium wilt and charcoal rot. In coastal areas with cooler soil temperatures, for example, ASD can actually exacerbate the latter two diseases, as the fungal pathogens feed on the rice bran.
“We know it works at warmer temperatures, but, practically, it's hard to do in coastal California,” Muramoto said. “It would be nice if we can find a way to suppress Fusarium wilt at a lower temperature, but we don't have it right now.”
That's why researchers emphasize that ASD is not a “silver bullet.” It's just one tool in the organic toolbox, which includes careful crop rotation, disease-resistant strawberry varieties and better diagnostic tests that help growers pinpoint outbreaks and make the application of various methods more targeted and more efficient.
And scientists will continue to optimize ASD to make it more effective and economical for growers in the different strawberry regions of California – from the Central Coast to the Oxnard Plain.
“We know it can work really well; it's just finding the most sustainable way to do this in our region,” Daugovish said. “We've got to just have an open mind and keep trying.”
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