Laser experiment hopes to save farm water. California USA

LOS ANGELES ( John Rogers, www.huffingtonpost.com)— Seventy-six years after the invention of the modern sprinkler helped revolutionize farming, lasers may revolutionize it again.
Jan Kleissl and a handful of his students at the University of California at San Diego think technology using laser beams might lead to a better way to conserve the millions of gallons of water sprayed each year on thirsty crops.
He and his team are using a large aperture scintillometer to study how much water crops lose to evaporation and the peak times that water disappears.
The hope is to give farmers a more accurate, up-to-date reading of how efficiently their crops are using water than current technology allows.
"What's new about our approach is the monitoring side of it," Kleissl said by phone from his office. "We're trying to improve on that."
Some advancements in irrigation have focused on water delivery system such as sprinklers. But while most farmers are experts at managing their irrigation by sight, recent years' droughts have called for more sophisticated ways to use and save water.
Water became an even more valuable commodity in California last year, when a federal judge ordered federal and state agencies to restrict pumping in the Sacramento-San Joaquin River Delta to protect the threatened delta smelt, severely cutting the growers' supply.
Further restrictions could result from last month's decision by state fish and wildlife managers to limit pumping to protect another native fish, the longfin smelt.
These shortages are prompting researchers to devise new ways to determine when to irrigate and how much water to use, said Khaled Bali, an irrigation expert for the University of California Cooperative Extension.
"There's not enough water to go around," he said.
San Diego County farmer Bob Polito, who was forced to remove 10 of his 60 acres of citrus and avocado trees from production after last year's pumping restrictions, said high-tech irrigation aids have so far been too expensive. But he said the increasing scarcity of water may force him to invest in technology to monitor his trees' water efficiency.
"Anything that gives you an accurate accounting on that score would be a help to farmers," Polito said.
Researchers also are testing a device that measures the velocity at which sap creeps up trees. When the sap's movement slows, growers would know that the trees need less water and reduce the amount that they use.
Other tests involve using satellite imagery to measure "evapotranspiration" _ the amount of water that seeps into the atmosphere from soil surfaces and plants. During periods of slow evapotranspiration _ when plants require less water _ farmers can cut down on irrigation.
Many farmers already use a formula based on historic evapotranspiration averages gleaned from meteorological data _ combined with on-site observations _ to devise their irrigation strategies.
But Kleissl's team hopes to give farmers more valuable information by using the scintillometer, which focuses laser beams across a farm field and records fluctuations of the refractive index of air that is caused by such things as changes in temperature and humidity.
What the device sees is similar to the waves in the air that people see emanating from the pavement of a highway on a hot day. But the scintillometer sees those waves in much greater detail. The hope is farmers can eventually use the lasers to more accurately measure the amount of irrigated farm water lost to evapotranspiration.
His study, which will take at least two years to complete, is unfolding on an experimental farm operated by the University of California. A field about a half-mile long and quarter-mile wide has been planted in alfalfa, a particularly thirsty crop. It is also the crop most commonly found in the Imperial Valley, some 200 miles southeast of Los Angeles, where rainfall averages fewer than 3 inches a year and high temperatures generally exceed 100 degrees for several months of the year.
Surveying half of the field is a scintillometer, while the other half is being farmed and irrigated conventionally.
If the tests show a substantial water savings, Kleissl would like to see scintillometers placed in agricultural areas around the state. He estimates that 10, which he says could cover a wide range of farm areas across California, could be installed for an initial investment of $500,000 to $700,000, although that wouldn't include the cost of maintaining and monitoring them.
David Zoldoske, who leads the International Center for Water Technology at California State University, said the scintillometer project shows promise, but would be best used in combination with other technologies that generate and analyze data on plants' water needs.
"It's simply just another way to have good information," he said. "It's like your doctor: If he can measure your pulse and some other things, that really helps him manage your health. It's the same with plants."
Note: A Scintillometer is a scientific device used to measure small fluctuations of the refractive index of air caused by variations in temperature, humidity, and pressure. It consists of an optical or radio wave transmitter and a receiver at both ends of an atmospheric propagation path. The receiver detects and evaluates the intensity fluctuations of the transmitted signal, called scintillation.
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Associated Press writer Jacob Adelman contributed to this story.