An annual check-up

02/01/2009 02:00:00 AM

By Tom Burfield

No matter what you grow or where you grow it, irrigation takes a big bite out of your annual budget, and inefficient watering can take a big bite out of your crop.

In fact, 90 percent of an agricultural business’ electricity bill likely is associated with water use, according to the Web site, http://www.flexyourpower.com, an energy efficiency campaign in California.

Growers and agriculture experts agree that the key to keeping irrigation costs under control is applying the right amount of water for the crop you’re growing and the climatic conditions under which you’re growing it.

By introducing simple energy efficiency improvements in your processing and pumping facilities, you can reduce energy costs by 10 percent, according to the Web site.

Aside from the cost and efficiency factors, shrinking water supplies due to drought and urban sprawl are reasons to monitor your irrigation system carefully.

“The trend toward irrigated agriculture seeing reductions in their water supplies is pretty universal,” says Tom Trout, water research leader for the Agriculture Agricultural Research Service in Fort Collins, Colo.

The amount of water growers need differs by soil type and crop, Trout says.

If you’re growing a standard field crop, such as alfalfa, overwatering won’t make much difference. But applying too much water to processing tomatoes, especially late in the season, can result in watery fruit that brings in less money.

Crops have needs
The best thing you can do to meet water demands and reduce use is to simply meet the crop’s needs, and those are related to weather, says Fedro Zazueta, professor of agriculture and biological engineering at the University of Florida Institute of Food and Agricultural Sciences in Gainesville.

“It is essentially weather that determines how much a given crop will use,” he says, but it’s up to you to deliver the water.

The type of irrigation system you use has everything to do with how appropriate your water application is, Trout says.
From an efficiency standpoint, drip irrigation holds the greatest potential, but sprinklers can have “reasonably high” efficiency, he says.

“Surface irrigation has the lowest potential efficiency,” Trout says.

He emphasizes that he is talking “potential” efficiency and points out that “anybody can mess up any system.”

Dual principles
Zazueta preaches the dual principles of efficiency and uniformity.

Uniformity means applying water evenly. Efficiency measures how well the amount of water you supply matches the needs of the plant.

Measuring uniformity is simple and can be done by the grower.

With a drip system, measure flow rates and times from different discharge points. With a pivot system, you can simply capture water in cans and compare the volumes.

For more specific information, Zazueta suggests consulting any of a number of publications listed on the IFAS Web site—http://www.ifas.ufl.edu.

Some drawbacks to achieving uniform application are pressure variations along pipes, manufacturer variations, using non-matching sprinklers and poor system design, he says.

Unlike uniformity, efficiency can be difficult to measure.

An estimate of water use must be established by measuring the amount of water needed by the plant over a long period, maybe a full season.

“Then you have to look at how much water you used,” Zazueta says. “If you had a crop that required 20 inches, based on weather, and you applied 40 inches, that means your efficiency is around 50 percent.”
 
Measuring methods
Several methods of determining how much water is adequate have been devised over the years, Trout says.

One is climatic irrigation scheduling, which involves measuring weather parameters, such as temperature and sunlight, to predict how much water a crop is using.

Another method is to monitor the soil with instruments to find out how much water is in the ground and adjusting your water use to an appropriate level.

Trout advises using both methods simultaneously.

One way to ensure accurate weather-related data is through agencies such as CIMIS—or California Irrigation Management Information System. The free, Web-based service comprises 140 stations that constantly gather weather-related information including temperature, humidity, radiation and wind direction, says Baryohay Davidoff, chief of agriculture, water management and financial assistance for the California Department of Water Resources in Sacramento.

This information provides a reference evapotranspiration number that can be used to calculate a crop coefficient, which can help a grower determine how much water to apply.

The site can be accessed by visiting http://www.cimis.water.ca.gov. Some other states, such as Washington, Oregon and Arizona, have similar but less sophisticated systems, he says.

Two factors should be considered when implementing an efficient irrigation system, Trout says—the system itself and management of the system.

For best results with the system, don’t skimp on quality, make sure sprinklers are not clogged, pipes don’t leak and irrigation ditches are in good condition.

On the management side, the best farmers have high-efficiency systems that are well maintained and well designed. And they either seek out consultants to help with their irrigation scheduling or hire their own people who help make decisions about when and how much water to apply, he says.

Keep up with technology
Savvy growers have found that staying on top of the latest irrigation techniques can result in a higher quality crop as well as substantial financial savings.

Until 1988, for example, Sam Accursio used 100 percent overhead irrigation at Sam Accursio Farms in Homestead, Fla. The 2,000-acre farm grows pickling cucumbers, squash and beans.

The system required 12 overhead pumps, 12 trucks, 12 workers and “12 sets of problems,” he says.

Then he switched most of his irrigation to a pivot system that required only one unit and less than one person to operate.
The pivot system is more efficient because it requires less pressure and applies water more evenly and closer to the plant. When the wind blew, the overhead system sometimes missed the crop by 3 feet, Accursio says.

The pivot system paid for itself within eight years, thanks to lower fuel costs. He estimated when he installed the system that it required 60 percent less fuel per 40-acre block to operate than the overhead system.

Waste not, want not
As ranch manager at VF Farms, which grows almonds, wheat and cotton near Fresno, Calif., Paul Betancourt has never had water to waste.

“We’ve always been very careful,” he says.

Orchards are “lasered flat,” which helps ensure an irrigation efficiency rate of more than 80 percent, even though the company uses flood irrigation, he says.

Betancourt uses skip-row irrigation for cotton, irrigating every other row. This technique not only conserves water, but it prevents the soil from becoming saturated, which can seal off the roots of the plants.

He also uses a pressure bomb—sometimes called a pressure chamber—from PMS Instrument Co. in Corvallis, Ore. It’s a chamber filled with nitrogen gas that measures plant stress caused by a lack of water, also known as the stem water potential.

VF Farms uses the device for cotton, but the PMS Web site—http://www.pmsinstrument.com—says it “has been shown especially helpful in the almond orchard.” It adds that plant-based measurements are “extremely helpful in keeping the orchard well irrigated for optimal growth but not over-irrigated.”

The University of California also has promoted pressure chambers for regulated deficit irrigation in winegrapes and almonds.



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