Flood irrigation still common, but drip method is gaining ground
02/16/2014 10:00 PM
10/22/2014 2:03 PM
The sight is not uncommon in California: water moving slowly across farm fields, in broad sheets or through a grid of ditches, propelled only by the pull of gravity.
Flood irrigation is a tried and true method of watering crops in California, promising thorough coverage with minimal investment. According to data from the state Department of Water Resources, 43 percent of California farmland in 2010 used some form of gravity irrigation, an imprecise method that uses relatively large amounts of fresh water and represents a big opportunity for water conservation.
Amid one of the worst droughts in state history, environmental advocates say farms are where the big gains in water conservation will come from, not in the residential and commercial sectors. That is because farms use 62 to 75 percent of all the water diverted in California for human purposes, depending on how that consumption is measured.
Broader adoption of solutions such as drip irrigation on farms, they say, could go a long way to stretch the state’s water supplies.
“There are still a lot of farms that are using very inefficient forms of irrigation, where you just basically release the water onto your field,” said Kari Hamerschlag, a senior agriculture analyst at Environmental Working Group in Oakland. “There should be some policy that holds farms to a higher standard.”
California farmers have actually made big progress over the past 20 years in switching crops to drip irrigation. In 1991, when California was experiencing its last major drought, 70 percent of farms were irrigated by gravity flow and only 15 percent by “low volume” methods, which include pressurized drip irrigation, according to the DWR data. By 2010, low volume methods had more than doubled to 38 percent.
The remaining portion includes sprinkler irrigation, which stayed relatively flat in that period: 15 percent in 2010 compared to 17 percent in 1991. Sprinklers also are considered a less efficient technique because, in some conditions, even more water is lost to evaporation and wind drift. But sprinklers are often needed to start seed germination in some crops – such as melons and peppers – before drip irrigation can take over.
“We’re seeing a long-term shift in agriculture to more efficient irrigation systems,” said Mike Wade, executive director of the California Farm Water Coalition. “It is huge, and it’s probably an under-recognized fact on what farmers are doing to improve their irrigation efficiency.”
Although state law requires urban areas to cut their water consumption 20 percent by 2020, there are no similar requirements for agriculture. Conservation advocates say there is a lot more that farms could be doing.
For instance, according to the DWR data, 13 percent of the state’s almonds and pistachios and 20 percent of its vineyards in 2010 were still irrigated by gravity. About 31 percent of tree crops in the broad “other deciduous” category also were watered by some form of gravity irrigation.
Annual field crops generally have a much higher use of gravity irrigation: 43 percent of the state’s fresh tomatoes, 78 percent of corn and 85 percent of sugar beets, for example.
“Low volume irrigation techniques are possible in every crop category here,” said Heather Cooley, co-director of the water program at the Pacific Institute, an Oakland-based nonprofit research group. “So it suggests there could be even greater shifts in some of these field crops.”
Flood irrigation is not always as wasteful as it seems, because often the surplus water runs back into surface streams or groundwater aquifers. But efficiency is harder to achieve, said Dennis Chessman, state agronomist at the Natural Resources Conservation Service, a branch of the U.S. Department of Agriculture.
“Surface irrigation tends to be more difficult to manage to get the highest efficiency,” Chessman said. “It takes a lot more work, and sometimes we don’t see the work put into it.”
‘A remarkable savings’
For decades, conventional wisdom held that drip irrigation wasn’t possible on field crops like tomatoes, alfalfa and corn because there was no way a tractor could operate in a field laced with fragile drip lines. Now, tractors guided by GPS systems can work these crops without touching drip lines. Buried drip lines can be left in the ground year after year as successive crops are harvested and replanted by machine.
“It’s opened up a wide array of crops that can be grown with drip irrigation that would never have been possible before,” Wade said.
One example is Joe Muller & Sons farm in Yolo County, which grows tomatoes, peppers and sunflowers. The farm runs a buried drip irrigation system on 650 acres in the Woodland area. Tom Muller, a partner in the business, said the farm has documented water savings as great as 40 percent. This cuts costs because it means the farm has to buy less water or pump less groundwater from its own wells.
“It’s such a remarkable savings, it’s just a no-brainer,” Muller said. “We’re trying to do the right thing. We talk about this every day.”
The farm had to adopt some new “cultural practices” after switching to drip irrigation, Muller said. For example, gophers and field mice will chew drip lines to get the water, which creates costly leaks.
To tackle gophers, Muller erected owl nest boxes in the fields to attract predators. Field mice, which don’t dig like gophers, are only a problem with sunflowers, which have to be dried out before harvest. This creates cracks in the soil that allow mice to reach the drip lines. So the farm began to apply a final dose of irrigation after the cracks open, which seals the cracks with mud.
Breakthroughs are also occurring on alfalfa, primarily grown as animal feed, where flood irrigation has long been considered the only acceptable practice. Now, some California farmers are growing alfalfa on drip, yielding huge water savings.
One is Ed Hale Jr., who grows alfalfa in the blazing-hot Imperial Valley. He converted a 2,600-acre alfalfa field to drip irrigation. Flood irrigation would have caused lots of water waste, he said, because the field sloped too much, causing water to run off too fast. He estimates drip uses about two-thirds less water, yet the crop yield has doubled.
“The drip is a little bit like having a patient on an IV,” said Hale, a third-generation farmer in the area. “You have an ability to deliver nutrients to that plant in a way that you don’t have in other ways.”
Cost can be a barrier
One barrier to drip conversions is cost: $1,000 to $3,000 per acre to buy and install drip lines, filters, pumps and controllers. It saves money on water, but often the investment can only be justified if it also increases crop yields, Hale said.
To bridge that gap, the federal government has paid out $100 million in grants over the past five years to help California farmers convert. These grants, part of the federal farm bill, typically pay 50 percent of a farmer’s cost.
The grants are managed by the Natural Resources Conservation Service, which has documented average water savings of 25 percent. The program is very popular. Muller, for example, received a grant for his most recent drip project on 50 acres of his Woodland-area farm. On the 600 remaining acres, he paid for the conversions himself over the past 11 years.
“We get far more requests for assistance than we have dollars to deliver,” said Dan Johnson, state water management engineer at NRCS.
Federal agencies, including NRCS and the Bureau of Reclamation, announced this month they will provide California an additional $34 million in drought emergency funds for water-conservation projects, including subsidies for drip irrigation.
But there are other barriers. One is that many irrigation districts are not equipped to serve drip irrigation. Most farm water is not delivered in pressurized pipes, the way drinking water is distributed to homes. Instead, most districts merely open a valve or gate to divert surface water into a gravity-flow canal or ditch that leads to a particular farm.
Also, irrigation districts have historically delivered water on long schedules to serve farms that use flood irrigation. This means a farmer might get water delivered only once a week, or even once every two weeks, for an occasional deep soak.
This doesn’t work for drip irrigation, where the water must be pressurized and needs to be delivered more often, albeit in lower volumes.
“It’s a heck of a scheduling strategy for many irrigation districts,” Johnson said.
When an irrigation district can’t provide the required flexibility and pressure, many farmers turn instead to their own groundwater wells. They have control over this supply and can pressurize it with a relatively small pump. But this is one of drip irrigation’s downsides: it can worsen groundwater depletion.
Drip also contributes little toward restoring groundwater volumes. With flood irrigation, a lot of water naturally soaks back into the aquifer, where it can be pumped out later.
“When you tighten the irrigation efficiency in the Central Valley, most of what you’re doing is reducing recharge to groundwater,” said Jay Lund, director of the Center for Watershed Sciences at UC Davis. “So you have a high technical efficiency on your farm and have not improved the efficiency of the Valley.”
Some irrigation agencies are converting their infrastructure to accommodate drip irrigation, including San Luis Canal Co. in the San Joaquin Valley. It is investing $1 million a year to build small reservoirs, or basins, to store irrigation water so it can be pressurized, and to install new valves, weirs and pipelines to manage pressurized water. It also has its own program to subsidize drip irrigation: grants of $250 per acre, and loans of another $250 per acre, to encourage farmers to switch.
“When these drip guys come in, they need water almost every day but in short spurts. We weren’t set up for that,” said Chase Hurley, general manager of the canal company, which serves about 45,000 acres. “We are now playing catch-up with some of our growers.”
Just six years ago, Hurley said, none of the farmers he served used drip. Now about 35 percent do. One reason is that tomato canneries prefer drip-irrigated tomatoes, because the yields per acre are better and the quality of the tomato is more consistent.
Hurley estimates drip irrigation has cut water use in his service area by 40 to 60 percent. As a result, the canal company now has surplus water, which it sells to neighboring farmers and irrigation districts. This has helped its bottom line and created a regional benefit, effectively allowing the same amount of water to serve more farms.
“Give me another 10 years and I bet you the majority of our acres will be on drip,” he said.
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