California Agriculture
California Agriculture
California Agriculture
University of California
California Agriculture

Current issue and featured articles

Special Issue
The Salton Sea
January-March 2022
Volume 76, Number 1
The Salton Sea: An introduction to an evolving system and the role of science
by Kurt Schwabe
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In this special issue, California Agriculture presents review articles that highlight what research to date can say about the changing Salton Sea ecosystem and its environmental and human health–related impacts, and identify areas in which further scientific research is needed to better inform policy. 

Peer-reviewed research and review articles

Ecological transitions at the Salton Sea: Past, present and future
by Timothy J. Bradley, Hoori Ajami, William C. Porter
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Mandated water transfers are rapidly changing the ecology of the Salton Sea and threatening crops, wildlife and public health.
The condition of the Salton Sea, California's largest lake, has profound implications for people and wildlife both near and far. Colorado River irrigation water has supported agricultural productivity in the basin's Coachella and Imperial valleys since the Sea formed over 100 years ago, bringing billions of dollars per year to the region and helping to feed households across the United States. The runoff, which drains into the Sea, has historically maintained water levels and supported critical fish and migratory bird habitats. However, since 2018, a large portion of the water previously allocated for agriculture has been diverted to urban regions, causing the Sea to shrink and become increasingly saline. This poses major threats to the Sea's ecology, as well as risks to human health, most notably in the noxious dust produced by the drying lakebed. To ensure continued agricultural and ecological productivity and protect public health, management of the Sea and surrounding wetlands will require increased research and mitigation efforts.
Microbiome interactions and their ecological implications at the Salton Sea
by Hannah Freund*, Mia R. Maltz*, Mark P. Swenson, Talyssa M. Topacio, Vanessa A. Montellano, William Porter, Emma L. Aronson
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Future studies of the Salton Sea should aim to characterize both the structural similarities and differences of the playa, sea and aeolian microbiomes.
Although the Salton Sea was once a thriving destination for humans and wildlife, it has now degraded to the point of ecosystem collapse. Increases in local dust emissions have introduced aeolian (wind-blown) microorganisms that travel, along with contaminants and minerals, into the atmosphere, detrimentally impacting inhabitants of the region. Proliferation of certain microbial groups in regions of the Sea may have a disproportionate impact on local ecological systems. Yet, little is known about how the biogeochemical processes of this drying lakebed influence microbial community composition and dispersal. To elucidate how these microorganisms contribute, and adapt, to the Sea's volatile conditions, we synthesize research on three niche-specific microbiomes — exposed lakebed (playa), the Sea, and aeolian — and highlight modern molecular techniques, such as metagenomics, coupled with physical science methodologies, including transport modeling, to predict how the drying lakebed will affect microbial processes. We argue that an explicit consideration of microbial groups within this system is needed to provide vital information about the distribution and functional roles of ecologically pertinent microbial groups. Such knowledge could help inform regulatory measures aimed at restoring the health of the Sea's human and ecological systems.
The drying Salton Sea and asthma: A perspective on a “natural” disaster
by Trevor Biddle, Rajrupa Chakraborty, Qi Li, Mia Maltz, Jo Gerrard, David D. Lo
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The changing ecology of the Salton Sea generates unique aerosol components that may contribute to the high rates of asthma in the region.
The Salton Sea is a drying salt lake in an arid region with high aerosol particulate-matter concentrations. This region is plagued by a high incidence of asthma, attributed in part to the aerosols surrounding the Sea. But the connection between the Sea and asthma may be more than simple calculations of dust concentrations. While dusts might contain toxic substances that impact the lungs of residents, the complex dynamics related to the environmental degradation of the Salton Sea may be generating additional toxins relevant to public health, such as microcystins produced by algal blooms. This collection of pollutants may be driving inflammatory responses in the lungs of residents through multiple mechanisms. As such, examination of the full range of potential environmental triggers of lung inflammation promises to yield a better understanding of key mechanisms driving the high incidence of asthma in local residents. Our discussion provides a perspective aiming to re-frame the issue in the context of the historical theory of “miasma” and the linkages between environmental change and health impacts.

Other peer-reviewed research and review articles

Impacts of winter cover cropping on soil moisture and evapotranspiration in California's specialty crop fields may be minimal during winter months
by Alyssa DeVincentis, Samuel Sandoval Solis, Sloane Rice, Daniele Zaccaria, Richard Snyder, Mahesh Maskey, Anna Gomes, Amélie Gaudin, Jeffrey Mitchell
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Results from a 3-year study suggest that processing tomato and almond growers can adopt winter cover cropping without changing irrigation practices.
As fresh water supplies become more unreliable, variable and expensive, the water-related implications of sustainable agriculture practices such as cover cropping are drawing increasing attention from California's agricultural communities. However, the adoption of winter cover cropping remains limited among specialty crop growers who face uncertainty regarding the water use of this practice. To investigate how winter cover crops affect soil water and evapotranspiration on farm fields, we studied three systems that span climatic and farming conditions in California's Central Valley: processing tomato fields with cover crop, almond orchards with cover crop, and almond orchards with native vegetation. From 2016 to 2019, we collected soil moisture data (3 years of neutron hydroprobe and gravimetric tests at 10 field sites) and evapotranspiration measurements (2 years at two of 10 sites) in winter cover cropped and control (clean-cultivated, bare ground) plots during winter months. Generally, there were not significant differences in soil moisture between cover cropped and control fields throughout or at the end of the winter seasons, while evapo-transpirative losses due to winter cover crops were negligible relative to clean-cultivated soil. Our results suggest that winter cover crops in the Central Valley may break even in terms of actual consumptive water use. California growers of high-value specialty crops can likely adopt winter cover cropping without altering their irrigation plans and management practices.
Soil health practices have different outcomes depending on local soil conditions
by Scott M. Devine, Kerri L. Steenwerth, Anthony T. O'Geen
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Soil organic matter can vary dramatically in different environments, regardless of good soil management practices. A new framework that considers regional soil types can help guide investments in soil health and help understand what can be achieved.
The amount of soil organic matter is a critical indicator of soil health. Applying compost or manure, growing cover crops, reducing tillage, and increasing crop diversity may increase soil organic matter. However, soil organic matter can vary dramatically in different environments, regardless of management practices. This calls for a framework to recommend place-based soil health practices and evaluate their outcomes. We used a new framework that groups soil survey data into seven regions in California's Central Valley and Central Coast. These regions either have performance limitations, such as root restrictive horizons, salinity, and shrink-swell behavior, or have relatively homogeneous, coarse-to-loamy soils ideal for agriculture. These inherent conditions affect a soil's response to practices designed to improve soil health. Looking at vineyards as an example, we find significant soil organic matter contrasts between soil health regions but not among contrasting management approaches within a given region. We also show that conservation practices improve or help maintain soil health in several long-term experiments, but inherent soil properties and types of cropping systems affect outcomes.

Early view articles

Improvements to the soil nitrate quick test for California small grains
by Taylor S. Nelsen, Michael Rodriguez, Ethan McCullough, Serena N. Lewin, Daniel Geisseler, Konrad Mathesius, Taylor Becker, Gabriel G. Rosa, Mark E. Lundy
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Inexpensive soil nitrate quick tests can help small grain growers identify their crops' nitrogen fertilizer needs.
Small-grain crop growers need to match their crops' nitrogen (N) needs with fertilizer applications. This can be challenging because small grains are grown under diverse conditions and their growing season interacts with unpredictable precipitation. Resulting conditions can lead to nitrate-N leaching and runoff losses. More widespread and accurate soil N testing could help growers improve N fertilizer use efficiency, reduce the risk of N loss, and fulfill regulatory requirements. Soil samples from across California small-grain growing regions were tested with a soil nitrate quick test as well as standard laboratory procedures. The quick test is inexpensive and easy to use, and it provides rapid results. A correction factor was developed to convert the quick test values to lab and fertilizer equivalents. The correction factor is based on site-specific soil bulk density and the extracting solution used. An interactive web-tool was developed that integrates this information for users. The quick tests provide accurate, real-time estimates of soil nitrate-N in the field to help improve fertilizer use efficiency and reduce N losses.
Winter flooding recharges groundwater in almond orchards with limited effects on root dynamics and yield
by Xiaochi Ma, Helen Dahlke, Roger Duncan, David Doll, Paul Martinez, Bruce Lampinen, Astrid Volder
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Almond orchards on soils with moderately high SAGBI or better can likely be used for winter water recharge with minimal negative effects and potentially some horticultural benefits.
California signed the Sustainable Groundwater Management Act (SGMA) into law in 2014. SGMA requires groundwater-dependent regions to halt overdraft and develop plans to reach an annual balance of pumping and recharge. Groundwater aquifers can be recharged by flooding agricultural fields when fallow, but this has not been an option for perennial crops such as fruit and nut trees. While flooding these crops might be possible during the dormant season, it is not known what impact flooding might have on tree-root systems, health and yield. We followed root production, tree water status and yield in two almond orchards in Northern California for 2 years to test the impact of applying captured winter water runoff for groundwater recharge purposes on tree performance. Results showed that more than 90% of the water applied to sandy soil and 80% of the water applied to loamy soil percolated past the root zones, with no measured adverse effects on tree water status, canopy development or yield. Groundwater recharge did not negatively affect new root production and tended to extend root lifespan. Based upon these data, applying additional water in late December and January is not likely to have negative impacts on almond orchards in moderately drained to well-drained soils.
Using Ecological Site Descriptions to make ranch-level decisions about where to manage for soil organic carbon
by Lina Aoyama, James W. Bartolome, Lucas Silva, Whendee L. Silver
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Rangeland conservation can keep carbon out of the atmosphere by storing it in the soil. Ecological Site Descriptions can help determine promising sites.
Maintaining and enhancing soil organic carbon storage can mitigate climate change while promoting forage growth. California has adopted incentive programs to promote rangeland practices that build soil organic carbon. However, there is no standard framework for assessing the baseline level of soil organic carbon at the ranch scale. Here, we use the Ecological Site Description — a land-type classification system — to help ranch managers set priorities about where to implement practices to increase soil organic carbon. We measured baseline carbon stocks at 0 to 15 and 15 to 30 centimeters' depth across three ecological sites and two vegetation states (shrubland and grassland) at Tejon Ranch, California. We discovered increased levels of soil carbon at ecological sites in higher elevations, and more soil carbon in shrublands as compared to grasslands. Slope, elevation, and soil texture, as well as plant litter and shrub cover, were significant predictors of soil carbon. The Ecological Site Description framework can serve as an important tool to help range managers keep carbon in the soil and out of the atmosphere.


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