Subsurface drip has benefit in some orchard situations

Subsurface drip irrigation, which is commonly used in many California vegetable crops, is far less common in orchards. But that may be changing.

Red Bluff prune grower Ken Lindauer is an advocate of subsurface drip irrigation, so much so that he has 400 acres of prunes on this type of system.

Lindauer's first subsurface drip irrigation system was installed 17 years ago, and his motivation then was the clay soil at the site that had a very slow infiltration rate.

"It's good dirt, but you just can't floodirrigate it," he said.

Arbuckle farmer Gerry Rominger uses subsurface drip irrigation in his almond orchards, but he says it isn't the best system for every orchard and it really depends on the soil type in the orchard. Growers need to determine what works best in the soil type they have before choosing an irrigation system, Rominger said.

Rick Buchner, University of California Cooperative Extension farm advisor for Tehama County, said that at this point he hasn't seen a lot of interest in subsurface drip irrigation in his county.

"It's a fairly difficult system, and a lot of people aren't willing to tackle that," Buchner said.

With his subsurface drip irrigation system, Rominger runs two lines of drip hose on each side of the tree about six feet from the trunk and 12 inches deep. The emitters are on a 40-inch spacing, and they are equipped with half gallon per hour emitters.

When Rominger plants a new orchard, he starts with surface drip and switches to subsurface drip irrigation about eight months to a year later.

"I have to get some root growth in a conventional way the first year that they're in the soil," he said.

Lindauer's drip is 16 inches deep and the drippers are spaced about 36 inches apart. Like Rominger, he has equipped them with half gallon per hour emitters.

Lindauer said there are many advantages to a subsurface drip irrigation system for his farm. First, the water goes directly to the roots. Second, with this type of system, there's no runoff, and third, there's no evaporation. He estimates his system is around 95 percent efficient.

Rominger said he also sees many advantages to a subsurface drip irrigation system. First, it has alleviated a problem he had with coyotes damaging the surface drip system by chewing the drip lines.

"If I bury it, I can turn on the whole system, and I don't even have to check it," he said.

Rominger has had problems with trees blowing over from the north wind. With the water applied six feet away from the trunk of the tree, he has less concern the trees will blow over because the trunk stays dry. He also thinks there may be less root disease because the tree trunk stays dry.

Another advantage to subsurface drip irrigation is reduced hand labor at harvest, Rominger said. When the sweeper blows the nuts on a surface drip system, the nuts get mixed in with the drip hose and hand labor is required to rake the nuts out and straighten the drip hose. With the buried system there are no hoses, so there's nothing to rake.

"A very expensive part of harvest is the hand labor with rakes," Rominger said.

Rominger also has had to do less weed control because there's no moisture down the tree row in the summertime, so the weeds don't grow. The weeds grow six feet out from the tree where the drip hose is buried, and he uses a 15-foot-wide mower to mow them.

"That's why I'm six feet away. I can control the grass with my mower, and I know I'm using less herbicide," Rominger said.

Root intrusion is a concern with a subsurface drip irrigation system.

"If you look at buried drip in other counties, root intrusion is a problem and root pinching is a problem," Buchner said.

Trifluralin, a root-growth inhibiting chemical, is used in subsurface drip irrigation to prevent root intrusion. It can be injected into a drip system, or it is impregnated into the emitters.

Root intrusion is Rominger's biggest concern.

"From time to time I've injected Treflan (root inhibitor) into the system in an effort to prevent root intrusion. I haven't noticed a lot of it, but it worries me. That's the biggest concern that I have with the subsurface drip, particularly as the trees age," he said.

Lindauer has subsurface drip irrigation with the trifluralin impregnated in the emitters and he has some that the trifluralin is injected. When he injects it, he uses an ounce an acre, approximately three times a year.

Squirrels and moles haven't been a problem, and Lindauer attributes this to the depth of the drip hose.

"It's 16 inches deep, and they're not that ambitious," he said. "We do have a lot of gophers, but so far no problems with damage to the drip hose."

Lindauer also uses owl boxes, and the owls help keep the gopher population under control.

Initially, Rominger had problems with gophers when the drip hose was about eight inches deep. After he went to 12 inches deep, he has had very little gopher damage.

The one downside to the subsurface drip irrigation is it can't be used for frost control, Lindauer said.

"You don't get cooling either, like if it's a hot day and you want to cool your orchard down. Not going to do it. So there are limits," he said.

Lindauer said subsurface drip irrigation can be installed in an established orchard, but installing in new orchards is preferable.

The benefits of subsurface drip irrigation far outweigh the negatives, Rominger said.

"I'm going to continue to do it. I've got at least 900 acres of buried tubing now on the farm," he said.

(Kathy Coatney is a reporter in Corning. She may be contacted at kacoatney@gmail.com.)