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Posts Tagged: grape
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.
The Achemon Sphinx Moth: A Lovely Beast, Indeed
It is indeed a “lovely beast,” as lepidopterist Art Shapiro, UC Davis distinguished professor of evolution and ecology, ...
Eumorpha achemon, the Achemon Sphinx, is a "lovely beast," says UC Davis distinguished professor Art Shapiro. Ann Sievers, owner, grower and miller Il Fiorello Olive Oil Co., recently found this one the wall of her patio. (Photo by Ann Sievers)
What's for lunch? A chicken in one of Ann Sievers' flocks at Il Fiorello Olive Oil Co., eyes the photographer. Chickens eagerly eat lots of bugs--if they're available. The larvae of the Achemon Sphinx moth feed on grape leaves. (Photo by Kathy Keatley Garvey)
Naturalist-photographer Greg Kareofelas took this image of an Eumorpha achemon larva in his yard in Davis several years ago. It was feeding on native grape, Vitus californica. (Photo by Greg Kareofelas)
An adult Eumorpha achemon, photographed by naturalist-photographer Greg Kareofelas in his yard in Davis several years ago. It was feeding on native grape, Vitus californica. (Photo by Greg Kareofelas)
Rest Stop at the Arrol-Metz House
One of my favorite things in the garden is getting to watch the hummingbirds. I enjoy watching them travel from flower to flower, trying a little nectar here, and then a little nectar there. I love it when the sunlight reflects off their throat patch, giving it that ruby glow. I am impressed by their moxie. They don't seem afraid of creatures much larger than they are. I love their chirrupy call and the sound their wings make. I've been watching them for years, so I thought I'd seen pretty much everything ...
Until a few mornings ago, I went to my window and saw a hummingbird going from grape leaf to grape leaf. I was really puzzled as I knew there were not any flowers on the vine, and only two clusters of grapes on that vine. As I got closer I saw he was rubbing himself on the leaf, then ducking his head and throwing back his shoulders, all while his little wings were just whirring away. He did this on several leaves, before it finally dawned on me what was going on. The sprinklers had just finished running and the grape leaves were sheeted with water. The hummer was cleaning himself in the water on the leaves, and seemed to be having a grand time.
He also seems to think that the tomato cages have been put out for his convenience to perch on and rest in between checking out gladiola blossoms. Hey, I am always happy to be of service.
The Nose Knows
Ask any gardener what their favorite plant is and I bet you will find they can’t name just one. Count me in that group. I love plants. But there are a few stand-outs that are worth mentioning.
For me, what captures my interest is either the color or smell of a plant. I love bright colors. Mostly oranges and blues. But I think that fragrance is the top attribute I look for in plants to add to my yard.
When I was attending Cal Poly, San Luis Obispo, I learned of this plant called Psoralea pinnata also known as the Scurfy Pea or the Kool-Aid® Bush. I had never encountered such a plant before. This was way back when I was just getting in to Horticulture, I was a late-bloomer with respect to learning or loving plants! (yes, pun intended) What caught my attention is the smell of the flowers. They smelled like grape Kool-Aid®! Seriously! The plant is somewhat ugly and rangy, but the blue and white flowers made up for that.
Since then, I have found a prettier substitute for the Scurfy Pea. This plant is in one of my favorite genuses, Salvia. The plant is Salvia melissodora known as the Grape-scented sage. It is a shrub that can get to 8 feet tall. It is native to the upper elevations of Mexico. The leaves also have an interesting smell, but not as good as the grapey fragrance of the violet/lavender flowers. To enjoy the smell, you have to avoid bruising the leaves, so don’t touch, just sniff. But be careful, as the carpenter bees and other bees visit this plant frequently. You don’t want a sting on your sniffer!
I have two of these salvias planted just outside my window. In the warm evenings of the summer, you can smell their delightful grape scent as it perfumes the neighborhood and of course, inside my home.
I recommend you open up your senses and try picking out plants with interesting fragrances to add to your own yards. You’d be amazed at what’s out there.
Grape-scented sage. (photo by Jennifer Baumbach)
Grape Turtles
The crape myrtles are blooming. Have you noticed? They’re pretty hard to miss, what with their beautiful blossoms in hot fuchsia, spicy red, pale lavender, pretty pink and clear white. These woody perennials thrive in Solano’s zones and offer year-round interest: peeling bark in winter and spring, blooms in summer, and fall leaf color.
I just stumbled across something I’d not realized about Lagerstroemia, the genus also known as crape myrtle. Not everyone spells it like that: CRAPE myrtle. Many spell it CREPE myrtle. Apparently, this is a long-running horticultural debate. Whether it’s spelled crape myrtle, crepe myrtle, crapemyrtle, crepemyrtle or crepe myrtles may simply be a geographical preference, or an evolution of language. In the U.S., the traditional Southern spelling is crepe myrtle (because the delicate flowers resemble crepe paper). Across the rest of the U.S. it is more commonly spelled crape myrtle, which is considered the French spelling. In Europe and Australia and other countries they use the scientific name, Lagerstroemia Crape Myrtle.
But I think my youngest child, Katie, has the best name for the shrubby little trees. As young as first grade, Katie noticed when Vacaville’s crape myrtles started to bloom. Knowing I love the beautiful colors, Katie would point them out: “Look, Mommy! The grape turtles are blooming!” Katie’s nearly 18 now and we still giggle when we notice summer’s explosion of crape myrtle blossoms.
Grape turtles indeed.
You say crape myrtle, I say grape turtle: Summer in Solano means the Lagerstroemia are in bloom. (photo by Kathy Thomas-Rico)
