Posts Tagged: SGMA
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.
You hear it every time drought returns to California: “Turn off the faucet when you brush your teeth.” “Collect shower water in a bucket before it warms up.”
While valuable, these tried and true drought resilience strategies can also deflect attention from the monumental challenges posed by droughts to natural areas, waterways, agriculture and people in California. Far-sighted and discerning management of the state's annual precipitation and groundwater is critical, particularly as droughts become more frequent due to climate change, said Faith Kearns, the academic coordinator of UC's California Institute for Water Resources.
“Like so many big societal problems, we don't want to get caught up believing individual actions alone will solve this problem,” Kearns said. “Conserving water in households can help people feel activated and certainly conserve some water. But, at the same time, it's not enough. We have big, systemic issues to deal with.”
Urban water use in homes, landscapes, schools and businesses amounts to about 10% of total developed water use in California, according to the Northern California Water Association. Irrigated agriculture uses 41%. The remaining 51% is used for water in rivers protected by state and federal laws as “wild and scenic,” water required for maintaining habitat in streams, and water that supports wetlands in wildlife preserves.
Traditionally, when surface water supplies for California farmers are cut during droughts, farmers pumped groundwater to bridge the gap. Over time, many of the state's groundwater basins have become severely depleted. In 2014, during a devastating five-year drought, the California Legislature passed the Sustainable Groundwater Management Act to regulate groundwater use in the state for the first time. The law aims for sustainable groundwater maintenance by 2040.
“We're in the implementation phase and local groundwater agencies are in various stages of developing and implementing sustainability plans,” Kearns said. “This is an opportunity for public participation to ensure all voices are heard in the effort.”
Of particular concern are underserved rural families who rely on wells for their household water. When the water table drops due to excessive pumping, the families can be left without water for drinking, washing and bathing. Small scale farmers often meet the same fate. Larger, neighboring farms may be able to drill deeper wells.
Wintertime flooding in permeable areas is one way groundwater can be recharged as it is used during the dry season. Getting access to water, developing infrastructure and flooding large farms will allow water to seep back into aquifers. Small-scale farmers can also be involved, said Ruth Dahlquist-Willard, the UC Cooperative Extension advisor to small-scale farmers in Fresno and Tulare counties.
“If there was a way to incentivize recharge on small farms, I think we could really contribute to groundwater management,” Dahlquist-Willard said. “It is not just about how we protect small farmers but also about how we involve them and have something that works for everyone's benefit.”
Fallowing land will likely be needed to meet the groundwater law's sustainability requirements. A 2020 report by UCCE specialist David Sunding and UC Berkeley professor David Roland-Holst, Blueprint Economic Analysis: Phase One Results, estimates about 992,000 acres of California farmland will go out of production, representing $7 billion in lost crop revenue and $2 billion in lost farm operating income.
The public can support smart and equitable water management by learning about decisions being made by their own local water providers and elected government representatives that impact the future of the California water supply. UC Agriculture and Natural Resources and its California Institute of Water Resources have gathered materials to serve as a starting point for understanding and advocating for sustainable water.
Listen to these episodes of the Water Talk podcast:
Find more on the UC California Institute for Water Resources website.
UC Cooperative Extension specialist David Sunding and UC Berkeley professor David Roland-Holst estimate that one-fifth of cultivated farmland in the San Joaquin Valley will be permanently lost as groundwater plans take hold and water supplies are severely restricted, reported Todd Fitchette in Western Farm Press.
The report, Blueprint Economic Impact Analysis: Phase One Results, says statewide the losses could total about 992,000 acres of farmland, losses of over $7 billion from crop revenue and a loss in farm operating income of nearly $2 billion.
The Sustainable Groundwater Management Act (SGMA) was passed during the 2011-2016 drought to return California aquifers to sustainable levels after decades of over drafting. Local agencies will ensure that groundwater extraction matches groundwater replenishment by 2040.
The report says the rise in almond acreage across the state will soon need to end as farmers in the San Joaquin Valley fallow more than 325,000 acres of tree nuts. Two-thirds of that acreage will be pulled from Fresno and Kern counties.
The labor market will also take a hit.
"We calculate that the direct employment losses from SGMA plus anticipated surface water reductions will total 42,000 jobs on average," Sunding and Roland-Holst wrote. These employment losses ... total $1.1 billion annually in the San Joaquin Valley."