Posts Tagged: flood
Study offers insights on reducing nitrate contamination from groundwater recharge
Light irrigation before flooding stimulates microbes to remove nitrates from soil
With California enduring record-breaking rain and snow and Gov. Gavin Newsom recently easing restrictions on groundwater recharge, interest in “managed aquifer recharge” has never been higher. This process – by which floodwater is routed to sites such as farm fields so that it percolates into the aquifer – holds great promise as a tool to replenish depleted groundwater stores across the state.
But one concern, in the agricultural context, is how recharge might push nitrates from fertilizer into the groundwater supply. Consumption of well water contaminated with nitrates has been linked to increased risk of cancers, birth defects and other health impacts.
“Many growers want to provide farmland to help recharge groundwater, but they don't want to contribute to nitrate contamination of the groundwater, and they need to know how on-farm recharge practices might affect their crops,” said Matthew Fidelibus, a University of California Cooperative Extension specialist in the UC Davis Department of Viticulture and Enology.
A recently published study by UC scientists sheds new light on how nitrates move through an agricultural recharge site and how growers might reduce potential leaching. Researchers analyzed data from two grapevine vineyards at Kearney Agricultural Research and Extension Center in Fresno County – one flooded for two weeks, and other for four.
Understanding initial nitrate levels crucial
A key factor in mitigating contamination is understanding how much nitrate is in the soil at the outset, said study author Helen Dahlke, a UC Davis hydrologist and leader of UC Agriculture and Natural Resources' strategic initiative on water. In areas with little precipitation and cropping systems that require greater amounts of synthetic fertilizer, the accumulation of residual nitrate – resulting from nitrogen in the fertilizer not taken up by the plants – can be quite high.
“The percentage of nitrates in some soils can really increase over the years, particularly if you have many dry years in a row where you don't have access to irrigation water or natural precipitation flushing some of those nitrates out of the soil,” Dahlke said.
While intense rains in recent weeks have helped dilute nitrate concentrations naturally, farmers looking to participate in recharge during the dry years ahead should consider flooding their fields with greater volumes of water.
“If you're doing this for the first time – on-farm recharge in the winter – check your residual soil nitrate levels because if they're very high, you should apply a lot of water in order to make sure that the residual nitrate is diluted down,” said Dahlke, who also added that growers should check their soil properties for suitability of recharge projects.
She recommended using, as a “good first approximation,” the online Soil Agricultural Groundwater Banking Index map, a project led by Toby O'Geen, a UC Cooperative Extension soil resource specialist.
Researchers looking at other ways to reduce nitrates
Even before flooding the fields for recharge, there are several practices that can lower initial nitrate levels and risk of leaching. Cover crops such as alfalfa and triticale, for example, can help take up residual nitrates that accumulate from fertilizing a main crop over time.
Dahlke and Fidelibus – a co-author of the San Joaquin Valley vineyard study – both pointed to pre-flooding irrigation that encourages denitrification, a process in which soil microbes transform nitrates into gaseous forms of nitrogen.
“Those denitrifying microbes need to be stimulated to do the work,” said Dahlke. “What we have found is that if you do a little bit of irrigation before you start the flooding, increasing the soil moisture can get those microbes started and they can take out more nitrate from the soil.”
The timing and quantity of fertilizer applications are also major factors in reducing leaching. Although more growers are following high-frequency, low-concentration practices to maximize uptake by crops, Dahlke said there needs to be more emphasis on incorporating nitrogen transformation processes – such as denitrification – in the nutrient management guidelines that farmers follow.
“Implementing thoughtful nutrient management plans will play a particularly important role in participating farms,” Fidelibus added.
A more holistic view of groundwater recharge
In short, choices made during the growing season can affect those in the winter recharge season – and vice versa. For example, applying compost or other organic amendments to soil can give microbes the “fuel” they need for sustained denitrification.
“What we have found is that our denitrifying bacteria often run out of steam because they don't have enough carbon to do the work,” Dahlke said. “Like us, microbes need energy to do the work, and for microbes this energy comes from soil carbon.”
Then, adding moisture via recharge to that field with high organic content can stimulate mineralization and nitrification, processes in which microbes transform the organic nitrogen into ammonium – and subsequently nitrates – that the plants can then take up. Those naturally occurring nitrates would thus reduce the need for the grower to apply synthetic fertilizer.
“The winter on-farm recharge experiments have shown that altering the moisture regime in the winter has consequences for the nitrogen budget in the summer growing season,” Dahlke explained. “Theoretically, what we need to be doing is better integrating both seasons by keeping an eye on the soil-nitrogen balance across the whole year so that we can ensure, at the end of the growing season, the residual nitrate in the soil is minimized.”
The study, published in the journal Science of The Total Environment, was part of the post-doctoral work of former UC Davis researcher Elad Levintal. In addition to Fidelibus and Dahlke, other authors are Laibin Huang, Cristina Prieto García, Adolfo Coyotl, William Horwath and Jorge Rodrigues, all in the Department of Land, Air and Water Resources at UC Davis.
/h3>/h3>/h3>/h3>Where, Oh Where, Can They Bee?
The nectarines are bursting into bloom, but where are the honey bees? Well, they're huddled inside...
A honey bee, cooped up in a hive for weeks due to the rain and cold, heads for a nectarine blossom in Vacaville, Calif. (Photo by Kathy Keatley Garvey)
Find the bee! There's one pollinating a nectarine blossom. (Photo by Kathy Keatley Garvey)
A pollen-packing bee exits a nectarine blossom.(Photo by Kathy Keatley Garvey)
The Nature Conservancy: Balancing People and Nature on the Sacramento River
The reach of The Nature Conservancy (TNC) is global, with projects that range from pristine...
USDA Farm Service Agency Elections
Santa Barbara/Ventura County Farm Service Agency Holds County Committee Election
The People Who Can Help After Disasters
Santa Barbara, Ca, June 18, 2019 – U.S. Department of Agriculture (USDA) Farm Service Agency (FSA) Executive Director Brenda F. Estrada in Santa Barbara/Ventura County reminds farmers and landowners that FSA is holding a 2019 County Office Committee (COC) Election. Producers, including minority, women and new farmers, are encouraged to participate in the 2019 election.
The county committee nomination period began on June 14, 2019. Nomination forms must be postmarked or received in the Santa Barbara/ Ventura County FSA office by close of business on Aug. 1, 2019.
For election purposes, counties are divided into local administrative areas (LAA). Each LAA nominates and elects one producer to serve a three-year term on the FSA county committee.
Each year, an election is held in an LAA where a committee member's three-year term is expiring. For 2019, an election will be held in LAA 3, which includes: The Eastern Area of Santa Barbara County from Santa Maria to the County line.
“Farmers and ranchers in LAA 3 are urged to participate in this year's county committee elections by nominating candidates by the Aug. 1, 2019, deadline,” said Estrada. “County committees are unique to FSA and allow producers to have a voice on federal farm program implementation at the local level.”
To be eligible to serve on an FSA county committee, a person must participate or cooperate in a program administered by FSA, be eligible to vote in a county committee election and reside in the LAA in which the person is a candidate.
Farmers and ranchers may nominate themselves or others. Organizations representing minorities and women also may nominate candidates. To become a candidate, an eligible individual must sign an FSA-669A nomination form. The form and other information about FSA county committee elections is available at fsa.usda.gov/elections. Nomination forms must be postmarked or received in the local USDA service center by close of business on Aug. 1, 2019.
Nationwide, there are approximately 7,800 farmers and ranchers serving on FSA county committees. These individuals make decisions on disaster and conservation programs, emergency programs, commodity price support loan programs and other agricultural issues. Committees consist of three to 11 members who are elected by eligible producers.
Persons with disabilities who require accommodations to attend or participate in this meeting should contact Brenda F. Estrada at 805 434-0396, ext. 2,
Brenda.Estrada@usda.gov
or Federal Relay Service at 1-800-877-8339, by Aug. 1, 2019.
fire 1
Fire Disaster Workshop for ALL Ventura/Santa Barbara Producers
The USDA's Farm Service Agency and Natural Resources Conservation Service will have workshops to aid agricultural producers; including cattle, tree, nursery, vegetable, and berry farmers in filing for federal assistance programs. Appointments can be arranged now for filing applications during these workshops.
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