Posts Tagged: vineyard

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.

UC Davis to build new $5.25M greenhouse to protect U.S. grapevine collection

Project designed to prevent red blotch and other grapevine diseases

A new, $5.25 million greenhouse is being built on the University of California, Davis, campus to safeguard an important grapevine collection from red blotch disease and other pathogens. 

The 14,400-square-foot greenhouse will have a vestibuled entry, be insect-proof and provide another level of disease protection. It is being spearheaded by Foundation Plant Services, or FPS, which provides the U.S. grape industry with high-quality, virus-tested grapevine plant material.

The program serves as the primary source for grapevine plant material distributed to nurseries under the California Department of Agriculture's Grapevine Registration and Certification Program, which provides the majority of grapevines planted in the United States. For the grape industry, it is essential to protect this material from disease-carrying insects and guarantee fast access to clean plant material.

“The program is considered the largest quarantine center for the grapevine industry in the United States,” said Maher Al Rwahnih, a plant pathologist and FPS director. “This is kind of a game changer for us.”

A history of serving the grapevine industry

FPS has maintained healthy grapevine planting stock on the UC Davis campus for more than 70 years in open fields at the Classic and Russell Ranch foundation vineyards. FPS scientists first detected grapevine red blotch virus at Russell Ranch in 2017. By 2021, an estimated 51.6% of the crop there was infected. Material from that vineyard is not being sold, and the site is now part of an epidemiological study to try to pinpoint how the disease is transmitted.

FPS pathologists have detected red blotch on less than 1% of the Classic vineyard crop. But it may not always be that way in the future.

“We don't know how long the Classic vineyard will remain clean,” Al Rwahnih said. “Every testing season, this is what keeps me up at night. We're not sure why it's happening in Russell Ranch and not the Classic vineyard.”

Once the greenhouse is operating, grapevines propagated from plant material from the Classic vineyard will be moved into the greenhouse, tested and verified as clean from disease. From there it will be sold to nurseries, which will grow additional plants to sell to growers.

Two greenhouses part of plan

Normally the foundation has 4,000 vines available, but the greenhouse will only house 2,000 vines, so inventory will be cut in half.

“This phase is just a starting phase,” Al Rwahnih said. “It's not sufficient for our needs.”

FPS plans to build another greenhouse in the next two to three years to increase capacity.

Industry groups and FPS identified greenhouses as the best way to protect the plants from red blotch and other pathogens transmitted by insects. They are also consulting with those same people on the grape varieties to include in the greenhouse.

“We have a large selection, and we need to make sure all the varieties that are important to industry are contained,” he said.

The first greenhouse is expected to be finished by the end of 2023.

Funding for the first greenhouse is coming from a variety of sources. The California Fruit Tree, Nut Tree and Grapevine Improvement Advisory Board, managed by the California Department of Food and Agriculture, contributed $4 million to the project. The California Grape Rootstock Research Foundation gave $500,000, Foundation Plant Services with UC Davis is funding $450,000, and the California Grape Rootstock Commission gave $100,000.

“This is crucial for the grapevine industry, and we are very grateful for the support,” Al Rwahnih said.

On the topic of vineyard nutrient management, farmers want to know about sheep

The UC Sustainable Agriculture Research and Education Program is working to build an online community for growers facing challenges and trying innovative approaches to how they manage nutrients on the farm. With the help of FarmsReach and Sustainable Conservation, we've been working to build up an online group based on nutrient management to discuss a wide array of practices. For two weeks in January, we hosted a discussion on nutrient management for vineyards, particularly in times of drought.

In a recent Capital Public Radio story on winemakers struggling with groundwater shortages this year, winemaker Chris Leamy said “the drought has helped to spur change and innovation.” When business as usual is not an option, farmers get creative. Through discussion, informational videos, and a tool kit of resources, farmers and UC advisors shared some of the creative ways that growers are adapting to water limitations and building healthy soil in their vineyards.

One discussion to rise to the surface throughout was the use of animals in vineyard systems. Farmers with experience running animals through their vineyards chimed in with valuable insights.

Some thoughts repeated by several growers were:

• Short breeds like babydoll sheep and tall cordons on vines make sheep less able to graze on the canopy. Some growers use electrified deterrents running parallel to the trellis to allow sheep to stay in the vineyard into the summer with no leaf damage. Growers who kept sheep in vineyards year round described eliminating mowing completely.
• Drip lines need to be tall enough to be out of reach from sheep.
• Move sheep frequently to prevent soil compaction.
• One grower runs chickens through the vineyard at the end of the season, but says to avoid the practice if shoot growth has been too vigorous — the added nutrients from the chickens may give vines an unwanted boost in the spring.
• Growers who use sheep in their vineyards describe significant nutrient inputs from sheep, some to the point of eliminating other fertilizers altogether.

You can follow more of the conversation here. The group of participants is growing (94 strong now!) and we'll be hosting future discussions on different topics. This project is hosted by UC SAREP as part of the Solution Center for Nutrient Management. You can join our mailing list to stay up-to-date with our activities, online discussions, and updates to our website.

UC study shows promise for protecting coastal winegrapes from frost

In California’s coastal winegrape-growing regions, a spring freeze can be devastating. Tender shoots and leaves burn back, causing damage that reduces the crop yield when it is harvested many months later.

“We’ve had some very severe frosts in San Luis Obispo County and on the Central Coast over the years,” said Mark Battany, UC Cooperative Extension advisor in San Luis Obispo and Santa Barbara counties. “In 2011 we had the most severe frost in 30 years and many millions of dollars of crop and wine value were lost because of that freeze.”

Farmers take various measures to protect their crops when temperatures dip below freezing, such as mowing or tilling the vineyard row middles, or running sprinklers with water pumped from underground aquifers or diverted from streams.

“Sprinkler frost protection is very effective in many areas,” Battany said. “The concern we have in California is that water is becoming more limited. We don’t have the ability to easily import water from other areas to our coastal regions, and our local supplies are being stretched quite thin.”

Some farmers are considering wind machines, which mix warmer air high above the ground with air closer to the ground to raise the temperature. But wind machines are expensive, and the potential effectiveness depends on the strength of the temperature inversion. UC scientists are now gathering data to help inform farmers before making the costly investment.

Battany and his colleagues - Rhonda Smith, UCCE advisor in Sonoma County, Richard Snyder, UCCE specialist in the Department of Land, Air and Water Resources at UC Davis, and Gwen Tindula, UCCE staff research associate - are collecting temperature inversion data at different locations in 60 coastal vineyards throughout three counties to document inversions during frost events.

The scientists installed 35-foot-high meteorological towers with data loggers at the top and at the five-foot height to measure the difference in temperature. In the first year of the study, there were useful inversion conditions on nearly three-fourths of the nights when there was frost.

“That’s a fairly good success rate,” Battany said. “The wind machine will provide quite a bit of protection under those conditions.”

The study will continue this year and in 2014. Farmers who wish to install their own meteorological towers with data loggers can do so at a cost of about $250 each. Installation instructions and specifications are available on the UCCE website.

The UCCE research is funded with a grant from the American Vineyard Foundation and a CDFA Specialty Crops Block Grant.

For more details, see the video below:

Winemaking venture initiated by former UCCE advisor

Former Fresno County UC Cooperative Extension farm advisor, Lowell Zelinski, and his wife are launching a new luxury winemaking course in Paso Robles to operate in conjunction with their agricultural management business, according to a story in the Santa Maria Times.

The Zelinskis began working with Central Coast vineyards in 2003; a few years later they began making wine from vines they were managing, a process documented by Becky Zelinski, an aspiring photographer.

Their friends were envious, the newspaper reported. "The Zelinskis then wondered if their friends’ interest could translate into a do-it-yourself winemaking business," wrote reporter Laurie Jervis.

In 2008, 14 friends and friends of friends spent a weekend in a cabernet sauvignon vineyard, picking and de-stemming the grapes by hand.

In 2009, the couple offered three weekend sessions on three different varietals. The weekends included meals prepared by a local chef to complement the varietal under study.

“These are the vineyards that we have relationships with all year," Mrs. Zelinski was quoted in the paper. "Many of the people (involved in those vineyards) are excited about our concept and want to help."

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