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Asparagus: It's all about root carbohydrates

Growing asparagus is all about root carbohydrate (CHO).

A Firebaugh, Calif., asparagus producer is among a growing number of producers who are turning to precision ag technology via the Internet and satellites to ensure that asparagus plants accumulate all the carbohydrates practical to maximize production of a crop that was first cultivated 2,000 years ago in the eastern Mediterranean region.

Greeks and Romans prized asparagus for its unique flavor, texture and reputed medicinal qualities. American consumers are rediscovering what ancient society appreciated, and consumption is increasing rapidly.

Asparagus is often called the Food of Kings. King Louis XIV was so fond of it, he ordered special greenhouses built to enjoy asparagus year-round. Early colonists brought it to America from France and England.

California is the asparagus capital of the U.S., producing more than 90 million pounds annually from about 30,000 acres with a value of about $150 million. Washington State is the nation's second largest asparagus supplier, producing about half of California's annual output.

Mexico is the American asparagus producer's biggest competitor, according to Stephen Smith, owner of Turlock Fruit Co., one of California's 200 asparagus producers.

“Labor is so much cheaper in Mexico. It is very difficult for us to compete with labor costs continually going up in California,” said Smith.

“It has become impossible to go head to head with Mexico because California asparagus growers have seen their workers compensation costs go up astronomically over the past few years,” said Cherrie Watte, executive director of the California Asparagus Commission in Stockton, Calif.

“My workers comp cost for the shed we operate near Firebaugh was $50,000 this year,” says Smith, who farms on the West Side of the San Joaquin Valley. “Mexico does not have costs like that.”

Hand labor cost

Hand labor accounts for more than 75 percent of asparagus production costs.

Asparagus is a perennial and Smith, like his counterparts, must find ways to reduce inputs because he cannot walk away from his 290 acres of six-year-old asparagus reaching its production peak. Asparagus stands remain viable for up to 15 years or more.

It costs about $1,000 per acre to grow asparagus; $2,100 per acre to harvest it by hand and $1,800 to shed pack it, according to Smith.

With labor costs continuing to rise, Smith must turn to the growing side of his production budget in search of reducing costs. He is using precision farming tools like satellite imagery, computers and an interactive Web site to slice into costs without sacrificing the all-important buildup and storage of carbohydrates and subsequently yields.

“Asparagus is a big user of water and fertilizers — 4- to 5-acre feet furrow irrigated. It uses 300 to 400 units of nitrogen and 200 to 300 units of phosphorous,” he said.

These high inputs are primarily to grow vigorous summer ferns to recharge the roots. Without full root CHO recharge, the early spring-harvested asparagus spears yield would be a disappointment.

“We have reduced water use significantly to about 3.2-acre-feet with drip irrigation,” said Smith. He is looking to reduce that even more along with lowering fertilizer cost without sacrificing yield and quality.

Precision technology

Asparagus responds beautifully to high fertility and water, but there is a point of diminishing returns. That is what Smith is trying to discover utilizing site-specific, precision ag technology.

Helping him achieve that goal is his consultant, long time San Joaquin Valley pest control adviser and agronomist John LeBoeuf, now president of CEO AgriDataSensing, Inc in Fresno.

LeBoeuf is a natural for exploring new technology. He was a member of the National Research Council's Committee on Precision Agriculture for the 21st Century that reported in 1997 precision agriculture technologies have the potential to revolutionize agriculture, but it must be validated in the field. What LeBoeuf is doing with Smith and his asparagus is realizing that potential.

Smith and LeBoeuf are using two different precision ag tools. One is a program called AspireUS imported to North America from New Zealand by Utah State University Extension Vegetable Specialist Dan Drost, who worked with the New Zealanders on maintaining carbohydrate levels there using Brix measurements of plant roots.

Asparagus growers have for years used summer fern development as a gauge to how much carbohydrates are being stored in the roots for next spring's harvest. The bigger the ferns; the more carbohydrates. Growers used tissue testing to make sure nutrient levels supported good growth.

Ferns go dormant in the winter and are cut off before the arrival of spring when workers gather ferns. Once harvest is over, the emerging spears are left to generate ferns to recharge the roots.

Drost says growers have long realized that visual evaluations are not always reliable indicators.

No correlation

“There is really no correlation between how little or how much top you have and root carbohydrates,” said Drost. “I have been in fields where ferns were over my head and produced only 3,000 pounds of asparagus per acre. And I have been in waist-high fields that produced 8,000 pounds per acre.”

New Zealanders developed a more reliable system using root Brix measurements year round from harvest through fern dormancy in the winter to give growers an ongoing indication of how many carbohydrates are in the root system. Brix readings are a strong indication of CHO levels.

“The storage root system is the engine that drives asparagus growth, and the size of the root system is the gas tank,” explained Drost.

Six times a year LeBoeuf takes root samples from 40 different sites in each of Smith's two fields near Firebaugh. He takes Brix readings using a garlic hand press and a hand-held refractometer and sends them via the Internet to the AspireUS Web site ( and receives recommendations quickly thereafter.

“We have tens of thousands of samples and history taken here and in New Zealand from probably 350 to 400 farms,” said Drost. Brix readings LeBoeuf sends in are interpreted against database readings and the history of Smith's own fields to come up with recommendations via the Web site for maintaining carbohydrate levels.

The carbohydrate content of the root system indicates how much gas is in the tank at any time of the year. Using that, growers can make better crop management decisions during the year.

Sample at harvest

For example, LeBoeuf takes root samples of Smith's asparagus during the harvest from mid February to May. If he finds carbohydrates are dropping below levels that will generate good summer fern growth based on AspireUS recommendations, Smith stops harvest.

Conversely, Drost worked with another grower who wanted to continue harvest late in the season to take advantage of good market. The AspireUS system told the producer he had adequate carbohydrate levels to continue gathering spears.

Readings can also reveal when there's too much fern growth, said Drost. Late in the growing season, adding new ferns may not be a good idea because it could bring down carbohydrates in the root and diminish harvest in the spring.

AspireUS readings also can assess irrigation management on carbohydrate recharge during summer fern growth and determine if pest or disease outbreaks are influencing carbohydrate recharge.

“It is not the carbohydrate level alone, but how big is the plant's root system; how full or empty is it depending on the time of the year,” said Drost.

Growers are charged to use AspireUS, which also allows growers like Smith to archive on the Web site recommendations, actions and results for year-to-year comparisons.

It costs $400 to set up a user on the network for up to 40 acres. Acreage above that is assessed at from $2 to $5 per acre.

It is a unique Web-based farm management program. While grower's information is secure, the database is managed by a public agency, Utah State University.

Drost took the idea of AspireUS to the California Asparagus Commission three years ago. It was validated on 12 sites throughout the state last year and offered to growers statewide this year.

Drost said there are about 4,000 acres enrolled in AspireUS in Arizona, California, Illinois, Michigan, North Carolina, Utah, Washington, Canada and Mexico.

Pleased by investment

“We absolutely could not be happier with our investment in AspireUS,” said Watte. The commission funds research projects and AspireUS is one of them.

LeBoeuf is pleased with the program and sees it as a complement to the area imagery he uses in the same fields.

“John has been a natural for this program. His work with aerial imagery and precision agriculture is a perfect fit, and Steve Smith also was eager to participate in the research we did in 2002 adapting the New Zealand work to California,” said Drost.

“John could see instantaneously how useful layering AspireUS and aerial imagery could be,” said Drost. “We plan to get together this fall and see how we may closer tie together satellite imagery and the AspireUS.”

LeBoeuf has been a leader in adapting satellite imagery to production agriculture. Besides his job as an agronomist and PCA, he also operates his own company analyzing visual information and is also a reseller of satellite imagery.

About 75 percent of his farmer clients currently use satellite imagery.

Pinpoint target

“One of the things that have held back growers and consultants until now in using satellite imagery is the cost. I can now get satellite imagery from DigitalGlobe for $1 per acre and it will pinpoint exactly the fields I want,” said LeBoeuf.

“You could not do that a few years ago. You had to buy large areas for a lot of money to get what you need. Growers were not willing to pay $1,800 for three miles by three miles of imagery,” said LeBoeuf.

Now there is competition among satellite imaging companies, and the cost has come down dramatically along with higher-resolution photography.

On Smith's asparagus, LeBoeuf is using DigitalGlobe imagery. Morgan Neville, western states regional manager for DigitalGlobe said satellites fly the San Joaquin Valley ever 48 to 72 hours and consultants and growers can order and download satellite imagery directly off the company's Web site for $1 per acre per image.

Satellite imagery works well for asparagus for no other reason than it is a very tall and rangy crop to scout. Fern growth can be well over 7 feet tall.

What LeBoeuf uses the green vegetation index satellite images for is to identify weak and strong areas of asparagus fields.

“Satellite imagery can often see what the human eye cannot see,” said LeBoeuf. That gives agronomists and pest control advisers a better start at solving problems.

“It is really a time management tool that allows me to go directly to areas identified as weak and see what the problems may be,” he said. “Satellite imagery still takes ground proofing to search out and identify the problem.”

Drip benefits

“Steve uses drip irrigation and that makes site-specific, precision farming work well because we can increase or decrease water or add nutrients as need by zones,” he said. “We don't have to treat the field as a whole. We can save money on water and fertilizer while maximizing production.”

It also allows LeBoeuf to compare areas within fields to evaluate why one area is different from another.

AspireUS and inexpensive satellite imagery represents the realization of the National Research Council's potential for precision agriculture to revolutionize agriculture.

e-mail: [email protected]

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