Posts Tagged: Sustainable Agriculture Research

Can California native plants be used as cover crops to benefit farmers and native ecosystems?

In late February, in an almond orchard in the Sacramento Valley, the fall-planted cover crop mix of grasses, brassicas and legumes had barely produced a green fuzz above the soil surface, and it was unclear when it would bloom. Unfortunately, this scene is becoming more frequent across California, as climate change causes more prolonged droughts and rain-dependent winter cover crops can barely grow, which delays or reduces bloom, essential for supporting pollinators. Fortunately, California native plant species have evolved with drought and have developed many strategies to survive and reproduce in those conditions.

Poor growth of cover crops during a dry winter. Photo by Sonja Brodt

 

Would it be possible to capitalize on the over 9 million acres of cropland in California for drought resilience and habitat restoration by utilizing more native species as cover crops? Our team at the UC Sustainable Agriculture Research and Education Program (UC SAREP) spent some time considering various native plant species and their potential ecological and operational attributes as cover crops. For a full list of species and their attributes, see https://ucanr.edu/sites/covercrops/.

Many native species are so well adapted to drought that they will still germinate and bloom during extremely dry years, for example, annuals like Tidy Tips (Layia platyglossa) and California poppy (Eschscholzia californica). Alternatively, perennial bulb species like Prettyface (Triteleia ixioides) and Bluedicks (Dipteronstemon capitatus) become dormant during the dry summer, retaining their bulbs below ground and re-growing when the rains return. These species could perhaps fit well in no-till orchard systems. Summer dormancy is important for tree nut growers because they usually need clean ground under the trees during harvest. Moreover, the costs to terminate and reseed would potentially be eliminated. While these species are well-known by Native Americans for their edible bulbs, at this point in time, we are not aware of any cover cropping trials having ever been conducted with these species. 

Cover crop growth with higher rainfall. Photo by Vivian Wauters

Another species with strong reseeding and more availability is the annual Lacy Phacelia (Phacelia tanacetifolia), which offers an intriguing historical precedent for developing a native species for cover cropping purposes. Native to California, it was introduced into Europe in 1832 by Germans. It is very attractive to pollinators and experienced a boom there in the early 1990s. European beekeepers and farmers have been using Lacy Phacelia as a cover crop ever since, and it has recently been gaining traction on California farms as well. California has many species of phacelia, with another, described as being even more attractive to native bees, being the annual Great Valley Phacelia (Phacelia ciliata). Besides supporting native bees, other native plant species can contribute nitrogen to the soil, such as annual Lupine (Lupinus spp.) and perennial Deerweed (Acmispon glaber), which are legumes and form an association with nitrogen-fixing bacteria in their roots.

Lacy Phacelia cover crop in a vineyard. Photo by Lauren Hale

Cover crops are not usually considered marketable crops. However, we should not preclude the potential for some plants that are useful as cover crops to provide a harvestable product as well. Native perennial fiber plants such as Indian hemp dogbane (Apocynum cannabinum), narrow leaf milkweed (Asclepsias fascicularis), and common nettle (Urtica dioica) could offer the opportunity to cultivate summer cover crops that have a market value, especially in cases where farmers are already willing to irrigate their cover crops to improve their development and amplify the benefits. Bowles Farming in the San Joaquin Valley is experimenting with growing these three species for fiber production. All three also attract native bees and important butterfly species such as monarchs (as long as farmers avoid spraying insecticides). 

While we believe that some native species could open new opportunities for farmers as cover crops, we still have insufficient studies testing the effects and viability of these species. Organizations like the NRCS Plant Materials Center at Lockeford and the Xerces Society are conducting practical studies with native species, creating plant guides and working with farmers to expand their use. In addition, researchers Lauren Hale of the USDA Agricultural Research Service and Anil Shrestha of California State University, Fresno, are using a 2021 UC SAREP small grant to study the effects of native species mixes on water demand and weed populations in San Joaquin Valley grape vineyards. Hale suggests that below-ground ecosystems may benefit as much from native plants as above-ground ecosystems. Says Hale, “Because plants and their microbiomes have evolved together for millennia, it seems logical that native plants would promote a good response from the native soil microbiota.”

For additional information:

UC SAREP List of California Native Species for Potential Use as Cover Crops: https://ucanr.edu/sites/covercrops/

Xerces Society lists of pollinator-friendly native species for California: https://xerces.org/pollinator-resource-center/california

NRCS California Plant Materials Center plant guides: https://www.nrcs.usda.gov/wps/portal/nrcs/publications/plantmaterials/pmc/west/capmc/pub/

UC SAREP Cover Crops Database: https://sarep.ucdavis.edu/covercrop

Powers of microbes: UC Davis graduate students get creative to teach farmers about soil microbiology

If you grew up in the 1980s or 1990s (or were a child at heart during that era), the famous Powers of Ten film likely left an indelible mark in your mind.

The film starts with a couple lounging on a picnic blanket and zooms out to the outer reaches of the universe, then back in to peer into the microscopic world of the human body: from white blood cells to DNA, and finally down to the proton of a carbon atom.

In its short 9-minute run time, Powers of Ten manages to inflame an existential angst about the size of a single human life while at the same time connecting the viewer to the beauty of the universe and the human body.

As a high school student watching the video, it filled me with the same sense of awe that I felt the first time I heard Carl Sagan's famous quote that “we are all made of star stuff.” 

Powers of Ten reminds us that looking at the world from different perspectives, from the very tiny to the immensely large, helps create a better understanding of the natural world, our place within it, and how we can impact it for good.

Had Powers of Ten returned from outer space by zooming into a piece of soil rather than a the human body, it would have explored the billions of living creatures in one handful of soil, slowly scaling down from millipedes to earthworms to ants to nematodes to protozoa, and finally down to the soil's bacteria and fungi that make up the base of the soil food web.

The video might then have looked a lot like the recent workshop at the Russell Ranch Sustainable Agriculture Facility, which served as a science fair for farmers and researchers to learn about the minuscule but powerful soil microbe.

PhD student Daniel Rath teaches principles of soil aggregates at Russell Ranch's recent Soil Health Workshop

Through hands-on demonstrations using everything from soccer balls to building blocks, sponges, and food coloring as props, graduate students and postdoctoral researchers in UC Davis' Soil Microbial Ecology Lab lead by soil microbiologist and professor Kate Scow explained the role and importance of these invisible players in soil to the people who depend on direct observation for much of their work: farmers.

While farmers often have a baseline knowledge about soil microbiology and its importance on the farm, “the science is evolving so quickly at this point, that it can be hard to keep up,” said attendee Margaret Lloyd, UC Cooperative Extension advisor  who works with small-scale farmers in Yolo and Sacramento counties.

The workshop coupled foundational principles of soil microbiology with practical on-farm management situations, making the case for farmers to actively consider soil bacteria, fungi, and other micro organisms in their decision-making process.

Jessica Chiartas, a fourth-year graduate student in soil microbiology and one of the workshop organizers, is somewhat of a soil science evangelist.

Her hope was to help workshop attendees better understand that “soils are not just physical, chemical systems. A majority of the processes that take place underfoot are biologically driven. Soils are living and breathing bodies and much like us, they need to be fed, covered, and protected from disturbance” in order to function in the long term.

PhD student Jessica Chiartas demonstrates how carbon sequestration differs in different soil types

Scaling down

The scale of microbial activity in soil makes it challenging to help farmers dig into just what scientists are talking about when they talk about microbes. 

“It's important to talk about the scale of microbes,” Chiartas said. “So much of what goes on in soils is mediated by microbes and the scale that they operate on is far different than the scale we measure them at. Our typical method of soil sampling and analysis is analogous to harvesting whole fields of crops, chopping them up, throwing them in a heap and then trying to glean information about the individual plants.”

The presenters at the soil health workshop used vivid analogies to translate the abstract results of scientific research and hard-to-imagine scales into concrete, relatable concepts.

A single gram of soil may contain a billion bacteria, and several miles of fungal hyphae, the web-like growth of fungus. Translated into human scale, the numbers are mind boggling.

If a single microbe were a 6-foot-tall person, then a single millimeter of soil would be as tall as the empire state building. A typical soil bacterium contains as many DNA letters in its chromosome as two copies of “War and Peace.” A stack of copies of “War and Peace” equivalent to bacterial DNA from a single teaspoon of soil would be larger than the Great Pyramid of Giza.

Radomir Schmidt explains microbial biodiversity

A soil information revolution

The metaphors of scale are a fun thought experiment, and they could provide a jumping-off point for a discussion between farmers and scientists essential for improving our current understanding of soil as a living system. Climate change is expected to amplify the  effects of soil erosion, compaction, nutrient leaching and other issues common in our current agricultural systems.

“We need improved management that works with the soil ecosystem to increase crop production while enhancing soil health,” said Radomir Schmidt, a postdoctoral researcher and workshop organizer. ”That's going to take a concerted effort and open dialog between farmers, scientists, and citizen scientists to discover, test, and implement these methods in the real world.”

We are now in the era of “soil information revolution," Schmidt said. As our knowledge of the soil microbiome expands, implementing this knowledge in agricultural practice is more and more possible.

This graduate student cohort is well-positioned to make the necessary connections, learning from farmers while helping them zoom in to see the essential lifeforms that impact their farm, then zoom out to help make decisions that are good for the farmer, good for the crop, and good for the microbe.

Farmers in the Davis area will have another opportunity to learn soil health fundamentals at a workshop this fall hosted by the UC Sustainable Agriculture Research and Education Program and Russell Ranch Sustainable Agriculture Facility. Details about the workshop will be posted here.

Postdoctoral researcher Radomir Schmidt discusses the scale and diversity of microbes in different agricultural management systems

Recording of life-cycle assessment of tree crops webinar posted

Trees, like this walnut orchard, store carbon.

Sonja Brodt, academic coordinator in the UC ANR Sustainable Agriculture Research and Education Program, and Elias Marvinney, a graduate student in the UC Davis Department of Plant Sciences, hosted a webinar on July 29 to discuss their life cycle assessment analyzing the environmental impacts associated with walnuts, prunes, peaches, almonds and pistachios. The researchers are quantifying energy use and greenhouse gas emissions in orchard crop production both on the farm and beyond.

Research by the UC Davis and UC Agriculture and Natural Resources scientists found that almonds have a relatively small carbon footprint and could become carbon-neutral or even carbon-negative, largely through incorporating orchard biomass into the soil or using the biomass, hulls and shells for renewable power generation and dairy feed.

To watch a free recording of the Life Cycle Assessment of Greenhouse Gas Emissions and Energy Use in California Orchard Crops webinar, go to http://bit.ly/1ITIbKr.  

Brodt and Marvinney co-authored two related articles published in the current issue of Journal of Industrial Ecology examining the environmental impact of the almond industry.

The first article, "Life Cycle-based Assessment of Energy Use and Greenhouse Gas Emissions in Almond Production, Part I: Analytical Framework and Baseline Results," is authored by Alissa Kendall, an associate professor in the UC Davis Department of Civil and Environmental Engineering, Marvinney, Brodt and Weiyuan Zhu, a UC Davis graduate student in horticulture and agronomy.

Marvinney is lead author of the second article, "Life Cycle-based Assessment of Energy Use and Greenhouse Gas Emissions in Almond Production, Part II: Uncertainty Analysis through Sensitivity Analysis and Scenario Testing," in collaboration with Kendall and Brodt.

This research was supported by grants from the Almond Board of California and the CDFA Specialty Crop Block Grant Program.

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