Deficit irrigation quandary for alfalfa growers

California wants to stretch out water supplies

Bob Krauter
Capital Press California Editor

February 9, 2007

Solving California's growing thirst by shifting water from alfalfa growers is a complicated issue that bears further study, according to water specialists and farmers.

UC-Davis water irrigation specialist Blaine Hanson, who has studied deficit irrigation in late-season alfalfa crops, said the practice is not currently being pursued by growers. State water officials are looking at ways to stretch limited water supplies in times of drought by shifting water from farms and compensating growers in a voluntary program.

"We have been looking at it in a project with the California Department of Water Resources to see if we could deficit-irrigate alfalfa during July, August and September to use as a strategy to make water available for urban and environmental interests during that period of time," Hanson said.

Most growers use flood or furrow irrigation for alfalfa, a multiple-harvest crop. Deficit irrigation, essentially cutting off water to the crop, means reduced yield.

"Yields go down considerably when you stop irrigating - about 25 percent of the normal yield. The ET (evapotranspiration) doesn't go down as fast. It goes down slowly and then levels off," Hanson said. "Basically, we have found an ET difference of about 8 to 9 inches by doing late-season deficit irrigation."

What complicates the issue of deficit irrigation in alfalfa is the fact that the water saved is calculated differently than if land is fallowed.

"It is not like fallowing a field where you would not have no yield, no ET. There is yield and there is ET, although we have found that yields we are getting from deficit-irrigated are not economically harvestable," Hanson said. "A grower would probably not harvest if he has a whole field that was under deficit irrigation."

Peter Brostrom, staff water and land use scientist for California's Department of Water Resources Office of Water Use Efficiency and Transfers, said the strategy is purely at the research level.

"I don't want people to get their water guns out. Right now, it is a feasibility study," Brostrom said. "It always would be a voluntary program so the grower would weigh what they would get paid vs. what their income would be from the alfalfa."

The alfalfa industry is being studied because an estimated 6 million acre feet of water is applied annually in California. If deficit irrigation could be used, it would offer the state a significant water savings.

"That's why there was some reason for looking into this," he said. The issue of grower compensation is one that experts are still wrestling with in examining the risks and benefits of deficit irrigation.

"There's significant crop loss with it, so you would hope that what growers received for the water they transfer is enough to cover that," Brostrom said.

Bob Ferguson, a Stockton, Calif., alfalfa grower with about 2,000 acres, would have challenges in using deficit irrigation. He has to apply water to push salt levels in the Delta soil lower.

"Over a given period of time, if you don't have something in the way to push those salts back down and keep them down, you will have problems," Ferguson said. "Typically, we would depend on winter rains, and (when) we get into a drought situation, that doesn't always work for us."

Ferguson is not aware of any discussion to compensate growers like him for shifting water from farms to other uses. His more immediate concern is keeping the water he has now.

"I don't think right here in the immediate area of the Delta it would be effective in resolving some of these water issues," Ferguson said. "We are struggling just to get enough water, period."

Jim Wegis, an alfalfa grower in Cuyama, in the high desert of Kern County, said water is a premium in his area and deficit irrigation is not practical.

"When we are irrigating at maximum, we are right above deficit. If we went down too much more, our production will suffer. If we don't irrigate, it won't even survive," Wegis said.

About 10 years ago the Resource Conservation Service did a study that helped local growers in his area to regulate irrigation water late in the season.

"That taught us a lot, and we managed to save a fair amount of water," Wegis said. "Our frequency couldn't change, but our total hours per set changed and we continued to shorten it a little bit as we got later in the year.

"That really helped us because we used to water a lot later and that showed us how much we were wasting."

One area of the state that has not received much study is California's Imperial Valley, which produces more than 10 percent of the state's $1 billion worth of alfalfa hay.

"In the Imperial Valley, some of the those late-summer irrigations amount to probably 40 percent of the water and produce maybe 25 percent of the crop, so there may be an ability to improve the efficiency of the water use if there is way to reduce stand loss and make it economical for growers," Brostrom said.

Brostrom, who works with UC-Davis' Blaine Hanson, said studies are looking into how to induce dormancy in alfalfa so that plants shut down quicker and use less water.

Studies will continue for another few years on deficit irrigation and will examine several areas of California - the Imperial Valley, the southern San Joaquin Valley, the Sacramento Valley and the state's intermountain alfalfa region.

Bob Krauter is the Capital Press California editor, based in Sacramento. His e-mail address is bkrauter@capitalpress.com.