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Posts Tagged: Samuel Sandoval Solis

New cover crop research can help groundwater sustainability agencies plan

Cover crops seem to offset their water use by improving soil moisture retention

This almond orchard near Durham in Butte County, shown in 2017, was one of 10 sites studied to determine soil water content in cover cropped versus non-cover cropped almond orchards and tomato fields from 2016 to 2019.

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 image shows a large field comparison of cover cropping and non-cover cropping in a Firebaugh tomato field where cover crop water use was studied. Cover crops build fertility, organic matter and water-holding capacity in the soil.

“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 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.


Posted on Tuesday, December 21, 2021 at 4:07 PM
Focus Area Tags: Agriculture

Drought is back! And so is Water Talk


Owens River north of Bishop. Photo by Dustin Blakey

The Water Talk podcast returns Friday, April 2, for its second season. This year's podcast will include a focus on the water issue on many minds at the end of a relatively dry rainy season: drought. As Water Talk co-host Faith Kearns says in the Season 2 preview episode, “in California, drought is not ‘if', it's ‘when'.” 


The second season will include a diverse group of guests from every corner of the state; border to border. “We thought a lot about the geography of the state, the identities of the people with whom we were speaking, and the experts we were talking with, and the topics,” says co-host Mallika Nocco.


The weekly podcast will feature discussions of agriculture, water policy, environmental and social justice, land and wildlife management, water for cities, Indigenous perspectives on water, climate change, and other issues related to California water. 



Some aspects of the podcast were modified in the second season as well. For example, instead of recording the podcast during a simultaneous live event, each episode was recorded with only the co-hosts. In addition, two production assistants supported the development of each episode. 


“The Water Talk team has new members!” the group tweeted. “We were thrilled to welcome ultra-talented Claire Bjork and Victoria Roberts as production support for Season 2, thanks in part to a UC ANR Renewable Resources Extension Act grant.”  


You can subscribe, listen and download all the episodes in Spotify, Apple and Google podcasts, as well as on the podcast's webpage. In addition to listening to the podcast, you can follow @podcast_water on Twitter for water-related news.


To catch up on Season 1 of Water Talk, visit


The Water Talk podcast is hosted by Mallika Nocco, UC Cooperative Extension specialist in the UC Davis Department of Land, Air, and Water Resources; Faith Kearns, California Institute for Water Resources academic coordinator; and Samuel Sandoval Solis, UC Cooperative Extension specialist in UC Davis Department of Land, Air, and Water Resources.

Posted on Thursday, April 1, 2021 at 5:34 PM
Focus Area Tags: Environment

Samuel Sandoval Solis shares his passion for water resource management

UC ANR's Samuel Sandoval Solis is featured on the cover of Vision Magazine.
The cover story in the most recent issue of Visión Magazine details the passion and expertise of UC Agriculture and Natural Resources' water resources scientist Samuel Sandoval Solis, a UC ANR Cooperative Extension specialist based at UC Davis.

Solis was born in Mexico City and began contributing to the family income at the age of 13 as a grocery store bagger. He earned a bachelor's degree in civil engineering at Instituto Politecnico Nacional.

When Solis was hired to help a community of 300 manage its water resources, he was nervous about his abilities, the article said.

"However, like many hardworking Latinos, Samuel put his fear and doubts to the side, and decided to pursue this great opportunity," wrote reporter Vanessa Parra. 

Solis earned a master's degree in hydraulics at Instituto Politecnico Nacional, and a Ph.D. in environmental and water resources engineering at the University of Texas, Austin. His research centered on the Rio Grande, a river shared by Mexico and the U.S. (Mexicans call the river Rio Bravo.)

"I was under friendly fire from people of both nations," Solis said. "Because I was doing my research in the Rio Grande/Bravo while living in Texas, people from the U.S. thought I was a spy and people from Mexico thought that I was a traitor," he said.

The language and culture barriers that Solis once perceived as negative characteristics became valuable assets when he joined the University of California. He is able to communicate with Spanish-speaking farmers on a personal level. 

Solis began his work in California just as it was caught in the grip of the current four-year drought. The dry period, he said, can be viewed as a "tipping point" to change the way the state uses and manages its water. His research focuses on water planning and management.

"We develop methods for finding strategies to better distribute water, ensuring adequate quality and the right timing," Solis said. "We consider the scientific, social, environmental, and economic aspects of basins. Our goal is to improve California's water management through cooperation, shared vision and science-based solutions."

Posted on Thursday, September 24, 2015 at 11:02 AM
Tags: drought (171), Samuel Sandoval Solis (3), water (81)

Optimizing irrigation may ease groundwater overdraft in Pajaro Valley

Pajaro Valley’s Water Management Agency electoral divisions
In the Pajaro Valley, an agricultural region in Monterey County, residents are being proactive about water conservation policies and seeking ways to save water. 

Groundwater makes up roughly 90 percent of the water delivered by Pajaro Valley’s Water Management Agency (PVWMA). There is a current overdraft of groundwater in the aquifers of this region, which calls for immediate action to protect their water source. Historically, the amount of groundwater in the aquifer was above sea level so the amount of salt water in the freshwater aquifer was kept at bay. Removing too much water from the ground at a faster rate than it is being replenished has caused seawater from the Pacific Ocean to enter the aquifer as the water level tries to even out. This seawater intrusion impairs water quality because saltwater is too saline for both agriculture and human consumption.

PVWMA is implementing seven different projects to control this seawater intrusion. One of these projects is their agricultural conservation program.

Agricultural conservation program

PVWMA asked Samuel Sandoval Solis, Ph.D., UC Cooperative Extension specialist in the Department of Land, Air and Water Resources at UC Davis, to help them with their agricultural conservation program. PVWMA wanted to know the volume water that could be potentially saved and the resulting economic impact of water savings on the valley. 

The key to agricultural water savings is to water a crop to its evapotranspiration (ET) value. The ET value indicates optimum water amounts that should be applied in order for the water to be completely beneficial to the plants. To estimate the potential water savings, Sandoval and his UC Davis team – undergraduate student Vicki Lin and Ph.D. students Jenna Rodriguez and Belize Lane – had to determine how many growers were surpassing a crop’s ET value.  The scientists interviewed growers to find out the volume of water each grower applied to the crops and the amount of money they invested in crop production. A statistical analysis was completed with applied water data of growers from PVWMA, information from the growers’ interviews, and expert-provided ET values to check for accuracy.

The scientists also analyzed land-use data sets from 2009 and 2011 for this project.  The analysis focused on 2009 because it was a normal year in terms of groundwater extraction. They determined that Pajaro Valley can save between 4,600 and 5,100 acre feet per year through conservation. This agricultural water savings program is anticipated to contribute to 41 percent of the region’s total water savings just by using water more efficiently.

Vegetable growers would take hard hit

Economic impact of water fee increase
This increase in water savings results in a direct decrease in revenue for PVWMA ranging from $842,000 to $929,000. To compensate for this loss in revenue, a potential increase in water extraction fee rates was analyzed. An increase in water fees will affect farmers, especially vegetable crop growers in the coastal region of Pajaro Valley because they already put 60 percent of their total net profits into their investment cost.  These coastal vegetable growers currently receive estimated revenue of $3,910 per growing season. If their water rates are increased by 50 percent, or $103/AF, their revenue will be decreased 6.7 percent ($265) per growing season. The economic impact graph at right shows how an increase in rates will affect farmers, substantially lowering their net profit on crops. Growers of strawberries, raspberries, blackberries and nurseries have a larger return on their investments, so an increase in water fees will not affect them as dramatically.

The full 37-page report on this project can be downloaded from a link at the top of

From left, project team Jenna Rodriguez, Belize Lane and Sam Sandoval. Vicki Lin not shown.
Posted on Wednesday, October 23, 2013 at 8:45 AM

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