- Author: Michael Hsu
In 20-year study, UCCE specialist Mitchell, colleagues, growers advance no-till and cover cropping practices
In the 1990s, long before “regenerative agriculture” was a buzzword and “soil health” became a cause célèbre, a young graduate student named Jeff Mitchell first learned about similar concepts during an agronomy meeting in the Deep South.
Mitchell was astonished to hear a long list of benefits attributed to practices known internationally as “conservation agriculture” – eliminating or reducing tillage, cover cropping and preserving surface residues (the plant debris left after harvest). Potential positive impacts include decreasing dust in the air, saving farmers money on fuel and equipment maintenance, improving soil vitality and water dynamics and a host of other ecosystem services.
“All of these things start adding up and you kind of scratch your head and say, ‘Well, maybe we ought to try some of this,'” recalled Mitchell, who became a University of California Cooperative Extension cropping systems specialist at UC Davis in 1994.
In 1998, Mitchell launched a long-term study of those practices at the West Side Research and Extension Center (REC) in Five Points, Fresno County. “We started this because, way back when I first began my job, nobody was doing this,” he explained. “This was brand-new, uncharted territory for California.”
For the next 20 years, Mitchell and his colleagues studied changes to the soil and ecosystem, learned from their failures and successes, and shared those hard-won lessons with fellow scientists and farmers across the state. A summary of their findings was recently published in the journal California Agriculture.
Conservation agriculture in California: ‘No trivial undertaking'
Mitchell and the Conservation Agriculture Systems Innovation Workgroup – a network established in 1998 comprising farmers, researchers, public agency personnel and members of private entities and environmental groups – started with a virtually blank slate. According to Mitchell, surveys at the beginning of the 21st century found that conservation agriculture practices were used on less than one-half of 1% of annual crop acreage in California.
Although no-till is common in the Midwest and Southeast of the U.S. and across wide swaths of the globe, it was almost unheard of in the Golden State. With the development of irrigation infrastructure in the 1920s, California farmers saw continually phenomenal growth in yield over the last century – and thus had little incentive to deviate from tried-and-true methods that relied on regular tillage.
Nevertheless, intrigued by the potential benefits of conservation agriculture, Mitchell wanted to see which of those practices could be feasibly applied to California cropping systems. During the 20-year study at West Side REC, the researchers grew a rotation of cotton-tomato, followed by a rotation of garbanzo, melons, and sorghum, and finally tomatoes.
But at first, it was a struggle to grow anything at all – as they had to master the basics of how to establish the plants in a no-till, high-residue system.
“This was no trivial undertaking,” Mitchell said. “Early on we struggled – we failed the first couple of years because we didn't know the planting techniques and we had to learn those. There was an upfront, very steep learning curve that we had to manage and overcome.”
Then there was the long wait to see any measurable improvements to soil health indicators, such as the amount carbon in the soil.
“For the first eight years, we didn't see any changes whatsoever,” Mitchell said. “But then they became strikingly different, between the no-till cover crop system and the conventional field without cover crops, and the divergence between those two systems became even starker.”
The two-decade time horizon for the West Side REC study is one major reason why it has been so valuable for growers and scientists alike.
“It's so hard to capture measurable changes in soil health and soil function metrics through research because those changes are really slow,” said Sarah Light, UCCE agronomy farm advisor for Sutter, Yuba and Colusa counties and a co-author of the recent California Agriculture paper. “Often in the course of a three-year grant you don't actually get statistically significant differences.”
Reaching, teaching and learning from farmers
The study site on the west side of the San Joaquin Valley also has been a vital teaching resource. Even though Light works with farmers in the Sacramento Valley, she has conveyed findings from that research with her clientele and uses soil samples from the site to vividly illustrate a significant benefit of conservation agriculture practices.
In one demonstration, she drops soil aggregates – which look like clumps of soil – into two containers of water. One clump, from heavily tilled land, falls apart quickly and the water becomes dark and murky. The other, comprised of soil that has been no-till and cover cropped for 20 years, holds together – a sign of healthy, resilient soil – and the water remains relatively clear.
“It's a really simple demo, but it's very effective because it shows how easily soil aggregates break apart with water – or not,” Light said.
That aggregate stability is a key factor in soil's ability to both move water (infiltration) and hold onto water (retention). Those dynamics are crucial for farmers to avoid ponding in their fields, preserve water for drier months, and generally endure the flood/drought whiplash of climate change.
Over the years, Mitchell has hosted thousands of visitors at the West Side REC study site to showcase the potential benefits of adopting soil-health management practices.
“I don't think I'm exaggerating in saying that this is probably the most-visited agricultural field station project in the history of UC ANR (UC Agriculture and Natural Resources),” he said.
Both the West Side REC – and Mitchell himself – are greatly valued by the local grower community.
“Jeff is a microcosm of the university's applied research on the West Side of the San Joaquin Valley,” said John Diener, who grows almonds, fresh market garlic, canning tomatoes, cotton, masa corn and wheat for production and seed on land adjacent to the field station.
Growers adopt, adapt and adjust practices
Tom Willey, a retired farmer and longtime collaborator with Mitchell, has actively encouraged peers to visit the Five Points site – especially in the early years.
“It was very innovative and there weren't many examples of that anywhere in the state,” Willey said. “So, I helped encourage people to go out there and learn and possibly think about doing similar work on their own farms.”
Willey himself was a pioneer in experimenting with no-till practices in organic vegetable cropping systems.
“As organic farmers, we were probably more tillage dependent than conventional farmers because it was the only method we had for weed control; we weren't able to use herbicides,” Willey said.
Despite early struggles, he persisted in trying different techniques and mechanical means of weeding. And Willey later partnered with a group of progressive vegetable growers and UC and California State University Chico personnel to secure a Conservation Innovation Grant from the Natural Resources Conservation Service to support more on-farm trials and share their experiences.
In the end, however, no-till proved too risky to continue, given the losses they incurred. One tricky issue is nutrient cycling. The organic growers found that after mowing down a cover crop and spreading compost, leaving those nutrients on the surface without incorporating into the soil through more vigorous tilling (or adding synthetic fertilizers, as conventional growers could do) results in lower yields. In the short term, farmers simply did not see yields that could sustain their operation.
“It's very difficult in vegetable systems, and particularly difficult in organic vegetable systems,” Willey said. “I would say a number of us have learned to diminish the over-reliance that we had on tillage, but not to completely eliminate it.”
Cover cropping is also a challenge for some farmers, with certain cover crops making a perfect haven for devastating pests such as lygus bugs and stink bugs, according to Diener.
“We do everything we can to eliminate the host crop from which they come, so why am I going to bring the enemies to my house?” he said. “It's about making enough money to be there next year. You're not going to be there next year with these pests. It's just not a practical management option, in light of our significant pest pressure and disease hosts for our crops of value.”
Instead of planting cover crops, Diener said he opts for mixing in grain crops that can similarly contribute to soil health – while generating revenue at the same time. According to Diener, a longtime collaborator with Mitchell, the best way to adopt conservation agriculture practices is to tailor them to specific localities and each grower's circumstances. And in his corner of the San Joaquin Valley, that means not following the template of the high-precipitation, no-till systems found in the Midwest.
“We've adapted Jeff's principles to our program; it won't look like Iowa to you, which is what everybody comes to expect to see. It ain't how it works, folks,” Diener said. “It's a different methodology. We do those things that fit our environment and that's why that West Side field station is important – because it's our environment.”
Promoting and enhancing soil health, one step at a time
More widespread adoption of soil-health management practices can be driven by a variety of factors. With the rise of drip irrigation in tomatoes, for example, more growers began using no-till or reduced till to minimize disruptions to the delicate driptape in their fields.
And, according to Mitchell, the dramatic increase in no-till practices in dairy silage production – from less than 1% to over 40% – was the result of entrepreneurial efforts by a small but extraordinarily dedicated group from the private sector that worked with farmers, one by one.
Because optimizing these practices requires close and intensive attention – and no small amount of courage and gumption – Mitchell and Light understand that growers might need to take an incremental approach. Even one fewer pass over the field, or cover cropping every other year, can provide some benefit for soil health, Light said.
“The value is that when you can prove the concept, then you can motivate every step of the way,” Light explained. “Jeff is showing the shining light of the goalposts, and that can motivate us to take every challenging step along the way.”
Shannon Cappellazzi, who helped with the data analysis on the recently published California Agriculture paper, agrees that there is value in taking a stepwise approach in building soil health.
Cappellazzi was the lead project scientist on the Soil Health Institute's North American Project to Evaluate Soil Health Measurements, which looked at 124 different long-term soil research sites across the continent – including the Five Points site.
After analyzing 2,000 samples from the various study sites, Cappellazzi said the evidence suggests that layering on each component of a conservation agriculture program – doing no-till, adding cover crops and then integrating livestock, for example – can have additive, cumulative benefits for soil health.
“I think having the data to show the long-term benefit makes people willing to do the short-term change, even if it's a little bit hard for a couple years,” Cappellazzi said.
The research at the West Side REC also produced another key takeaway.
“To me, what really stood out was that for most of the soil health indicators, cover crops had a huge impact. Both the cover crops that had no till – and the cover crops that had standard tillage – had considerably higher carbon and soil health indicator measurements than those without cover crops,” said Cappellazzi. She added that the data also indicated improvements in how the water moved into the soil, and how the soil held that water.
Vital research drives an enduring legacy
Water management and conservation, of course, will be paramount in California's increasingly volatile climate reality. Mitchell's Five Points research – and related studies across the San Joaquin Valley by UC Davis agroecologist Amélie Gaudin and others – contributed data that overturned a long-held belief about winter cover cropping.
“There's a lot of preconceived ideas about cover crop water use,” Mitchell said. “One of the things that we learned was that compared to bare soil water loss in the wintertime, cover crop water loss during that same growing period – from about November through March – tends to be almost a wash.”
That crucial finding provided researchers and soil health advocates with invaluable evidence to preserve the practice as an option for farmers.
“They've needed to go around and give a dog-and-pony show to a lot of Groundwater Sustainability Agencies (GSA) that had been on the brink of banning the growing of cover crops because the perception out there is that they use a lot of water,” said Willey, the retired vegetable grower. “But over the winter months, cover crops don't use a lot of water. In fact, they may not use any net water at all.”
The young researchers who studied cover-crop water use represent another important legacy of the Five Points study site. It has been an experiential training ground for many of the next generation of soil scientists, agronomists and ecologists.
“The number of students who have been trained by and through this study has been really phenomenal,” said Mitchell, noting that they have worked on topics ranging from air quality to soil carbon related to no-till and cover cropping.
Their contributions will be essential in continuing to refine and optimize these practices that are fundamental to conservation agriculture. On Diener's concerns about lygus bugs and stink bugs, for example, Cappellazzi – in her new role as director of research at GO Seed – is studying and breeding cover crops with an eye on characteristics that make for less hospitable habitats for certain pests.
Indeed, while the California Agriculture paper effectively wraps up the 20-year study at Five Points, its lessons will continue to resonate and inspire for years to come.
“This is a step in a long journey,” Light said. “It's a launchpad – this paper might be able to tie a bow on it in terms of the data collection, but in terms of the extension impact, this is really just the beginning.”
And for Willey, the omnipresent climate crisis compels the entire sector to pick up the pace along that journey.
“We've got a lot of pressure now to evolve agriculture very rapidly in response to climate change and I don't think we can sit around and twiddle our thumbs,” he said. “We know the directions we need to be heading – with more natural systems mimicry and less reliance on toxic inputs and synthetic fertilizers – and we need to figure out how to incentivize and support farmers in moving in those directions.”
- Author: Pamela Kan-Rice
Outstanding academics recognized with Distinguished Service Awards
Winners of the Distinguished Service Awards were announced June 13. Sponsored by UC ANR and Academic Assembly Council, the Distinguished Service Awards recognize service and academic excellence in UC Cooperative Extension over a significant period of time. The awards highlight the use of innovative methods and the integration of research, extension and leadership by UC ANR academics.
Award categories include outstanding research, outstanding extension, outstanding new academic, outstanding team, outstanding leader and contribution to diversity, equity and inclusion.
We are pleased to congratulate and recognize this year's honorees:
Outstanding Research - Mark Hoddle 
Mark Hoddle has been a UCCE specialist in biological control in UC Riverside Department of Entomology for 25 years. His research program on biocontrol of invasive pests that attack agricultural crops, threaten wilderness areas, and degrade urban landscapes in California has been supported by more than $14.5 million in grants from commodity boards and state and federal agencies and have significant impacts in California, nationally and internationally.
Highlights of his work include the successful biological control of the glassy-winged sharpshooter, a species of palm weevil (Rhynchophorus vulneratus), the Asian citrus psyllid and the Argentine ant, resulting in a massive reduction and elimination of these pests in California and other states and countries.
Hoddle also has developed proactive biocontrol and integrated pest management programs for pests not yet present in California but that are likely to invade, including the spotted lantern fly, the avocado seed moth and the avocado seed weevil.
His outstanding research has led to over 200 publications in peer-reviewed journals, books and book chapters. He also has published over 100 extension articles and 40 web pages. His outreach includes interviews for TV, radio, newspapers, magazines and podcasts.
In addition to his academic successes, Hoddle has mentored seven graduate students, more than 40 undergraduate students and nine post-graduate researchers. He also has received several national and international awards throughout his career.
Outstanding Extension - Lyn Brock 
Lyn Brock is the academic coordinator for statewide training for both the Expanded Food and Nutrition Education Program and CalFresh Healthy Living, University of California. Brock leads the training and professional development efforts for academics and staff that work at the state and county levels for both programs.
When the COVID-19 pandemic began, the EFNEP and CFHL, UC programs were stymied by the inability to provide in-person education. Through her persistence, innovation and leadership, Brock transitioned more than 140 program staff to virtual delivery in a matter of months so that they could continue to serve the people of California.
She spearheaded novel trainings pertaining to a wide variety of topics that suddenly became relevant, including learner-centered programming, online learning platforms and copyright policies, among others. Under her leadership, 24 evidence-based curricula were adapted for virtual delivery during the pandemic. These programs are still regarded by the programs' federally funded partners as cutting-edge in virtual education.
Brock has produced numerous limited distribution publications and also presented during conferences, trainings and presentations to extend knowledge in her role as training coordinator. Highlights of her extension work include the What's Up Wednesday meetings, virtual staff check-in meetings to facilitate communication between program leadership staff. She also developed training material and trained staff on available virtual platforms to allow them to deliver programs virtually.
Outstanding New Academic - Aparna Gazula 
Aparna Gazula became a UCCE small farms advisor in 2016. Her extension program provides training and technical assistance for nutrient management, pest management, irrigation and food safety to diversified vegetable farmers in Santa Clara, San Benito and Santa Cruz counties.
Because a majority of the crops grown by Asian immigrant farmers – including amaranth, bok choy, gai choy, gai lan, a choy, Chinese celery, edible chrysanthemum, yam leaves, garlic chives and pea tips – are considered minor crops, there is little research-based information about them that can be used as the basis for management decisions or to fulfill regulatory requirements.In six years, she has secured more than $1.6 million in grant funding for research, outreach and technical assistance to fill information gaps on pest management, food safety and water and nutrient management.
Many of the socially disadvantaged farmers Gazula works with face language and cultural barriers. To provide targeted extension to non-English speaking farmers, she secured grant funding to hire specialists and educators who are fluent in Cantonese and Spanish. With her team, Gazula provides technical assistance, workshops, and outreach publications in Chinese and Spanish.
She also has led her team in assisting farmers in the region to access pandemic relief funding and state programs to improve soil health and water use efficiency. Gazula and her team helped non-English-speaking farmers submit over 200 applications for relief between April and December 2020. These farmers received $3.1 million in emergency aid, allowing them to maintain vegetable production during the pandemic. With her team she also provided training and technical assistance, in both Cantonese and English, to farmers about the State Water Efficiency and Enhancement Program and Healthy Soils Program.
Although Gazula is a new academic, she is recognized throughout the region for her expertise and is often called on by community and local government groups to contribute to food and farming initiatives. She has established herself as a leader in supporting the Asian vegetable industry.
Outstanding Team - UC ANR Winter Cover Cropping/Water Use Team
The UC ANR Winter Cover Cropping/Water Use Team is composed of UCCE specialists Daniele Zaccaria, Samuel Sandoval Solis, Amelie Gaudin, Jeff Mitchell and Khaled Bali, UCCE advisor Dan Munk and UC Davis students Alyssa DeVincentis and Anna Gomes.
In direct response to prominent knowledge gaps around implementing the Sustainable Groundwater Management Act, the team conducted a focused applied research program on water-related impacts of winter cover crops in California's Central Valley from 2016 to 2019.
Their research showed that the benefits of winter cropping in processing tomato and almond production systems offset or compensated for water used during the winter by the cover crops. Contrary to widespread belief, research results showed that cover crops did not use a lot of soil water because evapotranspiration during this period is normally low, crops shade and cool the soil surface, and improve soil aggregation, pore space and soil water infiltration and retention.
This research provided the basis for a series of 11 invited extension education presentations and outreach activities to inform and guide policy implementation of local stakeholder agencies and entities including the Madera Regional Water Management Group, the American Farmland Trust's SJV Conservation Partnership Program, the CA/NV Chapter of the Soil and Water Conservation Society, and the East Stanislaus, the Eastern Merced, Fresno, Kings, and Tulare Counties Resource Conservation Districts, as well as the California Irrigation Institute.
Outstanding Leader - Gail Feenstra 
Gail Feenstra, director of the Sustainable Agriculture Research and Education Program, is a distinguished leader and visionary, not only in UC ANR, but across the food systems landscape. Her career has been exemplary in terms of her pioneering success in applied, multidisciplinary research, evaluation, and outreach. In the early 1990s, Feenstra began to parlay her graduate training in nutrition along with her experience in community development and food systems into what was then a very new, poorly studied discipline that she would continue to develop and lead for the next three decades.
This field of work comprises regional food systems that merge the business and livelihood needs of small- and mid-scale farmers with the economic well-being and nutritional health of their local communities. Feenstra developed SAREP's and the nation's understanding of values-based supply chains. She has been a pioneer in the farm-to-school movement and has developed widely adopted tools for farm-to-school evaluation. In recognition of her stature in this field, CDFA selected her to lead a four-year, $60 million evaluation of its Farm to School Grant Program.
Feenstra also has shown tremendous leadership within UC ANR through her role as co-chair of the California Communities and Food Systems Program Team where she has helped shape collaborations within UC ANR. She has worked to bridge interconnected disciplines of nutrition, food, health, community development and agriculture within UC ANR. She also has led efforts to work across program teams, particularly in developing new specialist and advisor position descriptions. Her energy is infectious and her leadership through collaboration is compelling. The Agriculture, Food and Human Values Society recently honored Feenstra with its 2022 Richard P. Haynes Distinguished Lifetime Achievement Award.
Outstanding Contribution to Diversity, Equity and Inclusion - Katherine Soule 
Katherine Soule began her DEI work in 2013, focusing on providing solutions to the challenges that marginalized youth, families and communities face on the Central Coast.
Her work particularly focused on the needs of Latino youth and families, LGBTQ+ youth and adults, neurodivergent people, and individuals living in poverty. Through a timely intervention, Soule's DEI work has helped to increase health equity, improve food security and safety, and promote economic prosperity in marginalized communities.
She implemented a very impactful “Schools as Hubs of Health” program that reached more than 4,000 students annually in more than 150 classrooms and created a college and career readiness pathway that engaged more than 12,000 youth. She brings an interdisciplinary approach to her work with an emphasis on engaged and participatory research, and lifelong commitment to personally unlearning and decolonizing.
Soule also demonstrates DEI leadership by serving on the UC ANR DEI Advisory Council as the inaugural chair and serving on the City of San Luis Obispo's DEI Taskforce.
- Author: Trina Kleist
Conservation Agriculture Systems Innovation has been named the 2022 recipient of the Conservation Innovation Award by the Soil and Water Conservation Society, an international organization based in Ankeny, Iowa.
“This is a very nice honor… and it has been achieved by, truly, the combined work and efforts of so many,” said Jeffrey P. Mitchell, UC Cooperative Extension specialist in UC Davis Department of Plant Sciences, who helped found CASI and has been instrumental in its leadership.
CASI, part of UC Agriculture and Natural Resources, started in 1998. It was formed by farmers, scientists and representatives of public agencies, private industry and environmental groups who aimed to develop knowledge and exchange information about the benefits of reducing tillage in agricultural lands.
Traditional practices such as tilling and plowing the land in preparation for crops are ingrained in agriculture. However, research has revealed that these practices cause soil erosion, dust and water run-off, and release greenhouse gases. In contrast, farmers and ranchers who have adopted the alternatives to tillage that CASI has been developing and evaluating see improved soil, better water infiltration and storage, less dust and lower costs, Mitchell said.
In the last 25 years, the no-till and low-till systems being explored by CASI have been widely adopted in much of the United States and in South America. But, in California's Central Valley, less than 1% of production acreage is farmed using conservation tillage. That's “largely because producers lack information, and successful examples of CT systems are only now being developed here,” CASI reported.
Now with more than 1,500 active members and affiliates, CASI conducts annual conferences to share research and the results of demonstration projects.
Mitchell's leadership of CASI praised
“Huge congratulations, Jeff, for your visionary and literally selfless leadership, always listening and learning, always humble. Thanks for taking us to new frontiers and possibilities of alternative futures. Thanks for showing us other ways to be a leader!!” – Kate Scow, UC Davis Department of Land, Air and Water Resources
“The team is special because everyone is sharing and learning as one. And, because your leadership has enabled us to all be more than the sum of the parts.” – Eric Kueneman, former global director of the United Nations Food and Agriculture Organization programs in Rome
“It was a pleasure to support the great work that this group does to change the farming paradigm in California.” – Cary Crum, California Ag Solutions
“Jeff is a modest person, but his achievements are numerous and span the gamut of extension, research and teaching. He has contributed enormously to our department through his innovative teaching, his inclusive extension work and his dynamic classroom teaching.” – Paul Gepts, UC Davis Department of Plant Sciences
The center's next project is to expand research and demonstration projects, acquire equipment, expand training and develop greater incentives for farmers to adopt conservation tillage in California.
- Author: Pamela Kan-Rice
Over a century of growing cotton in California, scientists and farmers have learned how to better manage soil health. To share their collective knowledge, they have produced a series of videos about cultivating better soil health in cotton fields.
At its peak cotton production, California harvested as much as 1.6 million acres of cotton in the late 1970s to early 1980s. Due to water shortages, growers harvested less than 200,000 acres of cotton in 2020.
“Although cotton acreage in California has fallen off in recent years, some rather impressive advances in soil health management in San Joaquin Valley cotton production fields have been achieved in the past couple of years,” said Jeff Mitchell, UC Cooperative Extension specialist, who formed the California Conservation Agriculture Systems Innovation Center with growers and production consultants.
In partnership with the Soil Health Institute of Greensboro, NC, the Conservation Agriculture Systems Innovation Center has released a four-video series on soil health in California cotton production systems (YouTube links below).
“The series of four videos chronicles not only the history of advances in soil health management in San Joaquin Valley cotton systems, but also some major progress that stems from both long-term research and very recent farmer and private sector innovation with new production paradigms,” Mitchell said.
“San Joaquin Valley farmers have done some really impressive work in recent years to improve the ways that they care for the soil in their fields,” Mitchell said.
To improve soil health, growers try to minimize soil disturbance, enhance biological diversity, keep living roots in the soil and cover the soil with plants and plant residue. They experimented with no tillage and cover crops. Researchers found that cotton fields using no tillage and cover crops achieved a higher soil aggregate stability score than standard tillage with or without a cover crop and no till without a cover crop. In no-till fields with cover crops, water infiltrated the soil in seconds rather than minutes.
The soil health videos range in length from 10 minutes to 21 minutes.
The history video traces important contributors and breakthroughs during the 100-plus years that cotton has been grown in California.
The second video features progress at improving soil health made by Cary Crum, formerly of California Ag Solutions of Madera now with Agritechnovation, Inc., and cotton farmers he works with in the San Joaquin Valley.
The third video chronicles the goals and findings of the unique 22-year soil research study that has been underway in Five Points as one of the Soil Health Institute's national program of long-term North American soil health study sites. It shows what is possible when the core soil health principles are implemented consistently in the region.
The fourth video on the importance of soil aggregate stability shows how attention to the dedicated soil health management principles can improve soil structure and overall production efficiency.
One important lesson from the study is that growers must be patient, improvements in the soil occur gradually.
“We did not see changes in many soil health properties or indicators during the first eight or actually 10 years of our study,” Mitchell said.
Videos on soil health in California cotton fields:
Soil health management systems for California cotton: A brief history https://youtu.be/7DWIJ_3QIz8
Recent advances in soil health management in California cotton production systems https://youtu.be/tRWk-d9F1I8
Local research base for soil health management in California cotton production systems https://youtu.be/AdqnsicuGYo
Regenerating soil aggregate stability in California cotton production systems https://youtu.be/K2fsvPTmlF0
- Author: Pamela Kan-Rice
Cover crops seem to offset their water use by improving soil moisture retention
Cover crop research conducted by a team of university researchers is now helping to inform and shape policy to implement the Sustainable Groundwater Management Act (SGMA) in several San Joaquin Valley counties.
“The Madera County Regional Water Management Group appreciates continued scientific discussions on SGMA-related issues, and especially enjoyed hearing from researchers on cover crops,” said Tom Wheeler, chair of the Regional Water Management Group for Madera County and a Madera County supervisor. “This is work that should be helpful to growers as they evaluate cover crops as part of their sustainable future.”
To help protect groundwater resources over the long-term, groundwater sustainability agencies (GSAs) are developing groundwater sustainability plans for their local regions.
"Our findings suggest that cover crop water use is negligible in most water years and the long-term benefits can help GSAs meet their management goals,” said Alyssa DeVincentis, a former UC Davis Ph.D. student who worked on the project. “How cover crops impact soil moisture depends on species and management history, but generally soil moisture at the end of the winter season did not differ between fields with winter cover crops and clean cultivated soils."
From 2016 through 2019, UC Agriculture and Natural Resources researchers and their collaborators amassed very large data sets from almond orchard and tomato field sites located between Chico in Butte County and Arvin in Kern County. They used the data to quantify changes in soil water storage and evapotranspiration that occur under cover-cropped and bare fallow conditions during the winter cover crop growing period – about November to March.
The research team includes UC Cooperative Extension water specialists Daniele Zaccaria, Samuel Sandoval-Solis and Jeff Mitchell based at UC Davis; DeVincentis now of Vitidore, Inc.; and Anna Gomes, Ph.D. student at Stanford University.
The GSAs must first quantify the amount of water going into the groundwater bank through rainfall and surface water irrigation versus the amount of groundwater being removed at all farms within the GSA's jurisdiction.
“To do this, many local GSAs are turning to remote sensing and modeling of evapotranspiration, or ET, to provide data on the regional balance between groundwater depletions versus recharges,” Mitchell explained.
“Because winter cover crops may appear on remote sensing images as water-using vegetation, the sole use of model-driven data coming from satellites could become a disincentive to the practice being used.”
“This approach may not account for the important benefits that winter cover crops provide San Joaquin Valley farmers like Justin Wylie, a Madera County almond and pistachio grower who works with the research team,” Mitchell said. “He has experienced the benefits of winter cover crops firsthand, including increased water infiltration, habitat and carbon for soil organisms, and reduced water run-off.”
Cover crops grown during the winter may not use a lot of soil water because ET during this period tends to be low. They also provide shading and soil surface cooling, which help reduce soil evaporation. In addition, Mitchell said that cover crops can improve soil aggregation, pore space and soil moisture retention.
Together, cover crop benefits seem to offset or compensate for their actual water use during the winter.
“Because GSAs need reliable and accurate information related to this important issue and to possible shortcomings of relying solely on remote sensing as the way to go, our research has been particularly timely in the context of SGMA,” said Daniele Zaccaria, associate professor and water management specialist in UC Cooperative Extension at UC Davis.
A presentation about their cover crops research is available on YouTube at https://youtu.be/x3xQlZ9EdCk. The webinar is intended for water agency personnel, but the information is relevant to anyone who is interested in how cover crops may influence San Joaquin Valley cropping systems and the water cycle, Mitchell said.
A peer-reviewed article about this cover crop research, “ “Impacts of winter cover cropping on soil moisture and evapotranspiration in California's specialty crop fields may be minimal during winter months,” will appear in the first quarterly issue of California Agriculture in 2022.
