Evolution of an irrigation system
Just over 15 years ago on a small Kerman farm, a significant irrigation study was conducted as an almond and table grape grower prepared to switch from flood irrigation. The result was not only proof that drip irrigation was highly efficient; it was also the beginning of an irrigation evolution on the Lehman farm.
The study was devised and monitored by the Center for Irrigation Technology at California State University, Fresno, on the Steven E. Lehman farm. Since his passing six years ago, the 80-acre farm has been managed by son Karl, the fourth generation of Lehmans to farm. For a hundred years the farm had been using flood irrigation, but in 1993 a 40-acre field was converted to 18 acres each of surface drip and subsurface drip.
The three-year study looked at root distribution in sandy loam soil and provided yield and management information. Despite problems with clogging and maintaining uniform pressure, the Thompson seedless grapes responded to both surface and subsurface drip. The systems all yielded right around 4,000 pounds per acre. Drip in subsurface lines provided the most efficient system, but Netafim surface lines gave the highest yield with the lowest root-zone stress. Compensating emitters performed better than noncompensating.
Steve Lehman’s system was in place for 15 years. Now his son is faced with a decision. He has ripped out those Thompsons and wants to plant almonds. Karl is torn between surface drip and fan-jet micro sprinklers, the system that his father installed on their 40 acres of almonds in 1999. He says that system is efficient and gives high yields. The trees averaged 4,000 pounds of almonds in the three years prior to 2009, when production fell to about 2,900 pounds due to nonirrigation factors. The micro sprinklers produce a crop with about 4 acre-feet of water.
“You do better irrigation management with drip,” says Lehman, who has gone back to Cal West Rain, the company that installed those experimental drip systems, for a new system design.
The new options
Susan Rathbun, the Cal West Rain designer of the 1993 drip systems, is now designing two options for Lehman’s new almonds, which will be planted in 2011. The two options will be micro sprinklers or double-line surface drip: one line on each side of the new trees.
“The jets cover a larger surface area,” Rathbun says. “We usually use the jets in sandy soil,” because the underground wetting pattern is more suited to large trees. She says water usage in the proper environment is about the same for the two types of systems. One benefit of sprinklers is frost protection on cold nights. Actually, Rathbun says, one of the best systems for trees is subsurface drip lines. It is efficient, but avoided by almond growers; a buried system can’t be monitored as closely, and leaks may have to be detected by monitoring water flow.
“Jets are more expensive to install,” she says, because while drip can be run off one orchard set of this size, micro sprinklers may require two or three sets. That’s more hardware to purchase and monitor. Rathbun says Lehman is following in his father’s footsteps as a progressive grower curious about technology, and not afraid to use it.
New in the 2011 system, she says, is possibly a computerized controller, digital flow meter and irrometers that will allow data logging. Lehman could run the system with a laptop using evapotranspiration information from online weather station data. If he elects sprinklers, she will recommend the same Olsen Ultra Jets used for the existing almonds. If he opts for drip, she likes nonpressure-compensating in-line emitters, with pressure regulators on each riser.
Lehman’s primary challenges to both systems are biological. He has a problem with coyotes along the nearby San Joaquin River chewing up his drip lines. And in this sandy soil, gophers in his almond orchard are eating his supply lines.
“We’re leaning toward the double-line drip,” he says. Another problem he has with the micro sprinklers is that during harvest, the heads can be damaged and the jets clogged by almond harvest equipment. With double drip, he will just have to put up with the coyotes.
Dale is an Altadena writer.
• Lehman’s father switched from flood to surface or subsurface drip.
• His decision is between micro sprinklers and double-line surface drip.
• The irrigation choice is complicated by coyotes and gophers.
This article published in the January, 2010 edition of CALIFORNIA FARMER.