Nov 12, 2013

Overhead pivot irrigation gaining traction in California

The ability to conserve water and labor are two of the most critical factors for growers in being able to save money and maximize resources. At a recent Precision Irrigation Conservation Agricultural Farm and Field Station tour hosted by Conservation Agriculture Systems Innovation in Five Points, Calif., researchers and farmers discussed how new innovations in overhead pivot technology and conservation tillage can help farmers become more profitable.

Overhead irrigation pivots are generally comprised of a series of pipes about one-quarter of a mile long, joined together and mounted on wheeled towers that move in circular patterns around the field and deposit water with sprinkler heads attached to hoses.

Growers have the ability to control how much water gets applied, as well as when and where the water gets delivered. They can also use overhead systems to apply insecticides, pesticides and fungicides. Since the water gets applied so uniformly throughout the fields, it doesn’t matter if the terrain is not completely flat. This is a big advantage for growers who work with uneven ground.

The problem of uneven ground is often a big issue for growers. One grower at the field event had been thinking of spending $300,000 to laser his field. Instead, he decided to invest in three overhead irrigation pivots.

USDA’s Natural Resources Conservation Service did a 50 percent cost share that made it possible for the grower to purchase the pivots, according to Rick Hanshew, an irrigation specialist with Agri-Valley Irrigation who helped install the pivots.

Aside from being able to use the overhead pivots on uneven ground, another big advantage is that growers can save large amounts of money on labor and workman’s compensation, Hanshew said. Many growers can reduce their irrigation labor force by 80 percent and do most of the work themselves. A grower can, in fact, do most of his irrigation work simply by using his smartphone to tell the overhead pivots when and where to run. If there’s a problem with any of the pivots, the grower will automatically get a text message letting him know if there’s a wheel stuck somewhere or a sprinkler that’s not working.

Over the years, there have been huge improvements to the pivot systems. For instance, instead of spraying water out in front of the tires as they rotate around the fields, the pivots now have sprinklers that spray water behind the tires, according to Scott Schmidt of Farming “D” in Five Points.

“When you have the sprinklers going behind the wheels of the tires, it keeps the water off the tires and eliminates wheel tracking issues, making it that much easier to use,” Schmidt said.

Schmidt began with seven center pivots about eight years ago.

“What I liked about them was they worked really well and were low water users,” Schmidt said. “I also liked how you could control exactly how much water you wanted to put down and the fact that you slow the pivots down or speed them up.”

While the overhead systems might seem cost prohibitive to some at first, over the long run they could be less expensive than drip tape, according to Karen Klonsky, an agricultural and resource economics specialist at the University of California, Davis. Generally, overhead pivots cost $500 to $900 an acre. With a drip system – depending on the type of drip tape a grower chooses – it can cost $200 to $400 an acre. Other costs start adding up when growers factor in the extra $20 to $30 per acre it costs to put sulfur acid and chlorine to keep the drip tape from clogging up, and then the additional $30 an acre to flush the system. Then, there’s the cost of disposing of drip tape once it has to be replaced. Generally, drip systems last a maximum of nine to 10 years, whereas overhead pivots have a lifespan of 20 to 25 years. It’s also important to note, she said, the overhead pivots give growers much more flexibility in crop rotations than drip systems.

John Diener, president of Red Rock Ranch, agreed that overhead pivots, over the long run, are less expensive than drip. Although both drip and pivot have about the same water efficiency – about 92 to 95 percent – pivot systems, unlike drip, don’t clog, have problems with root intrusion or rodent damage.

Another advantage of the center-pivot systems – aside from the labor savings – is the fact that they seem to do a better job of leaching salinity out of the soil than drip. The reason for this is that center-pivot irrigation pushes water straight from the top over the fields. So the water is only moving in one direction: down. With drip, the water moves out into the soil in a circular, halo-type pattern, Diener said.

“You have downward movement with the water with drip, but you also have upward movement and side movement, and there never seems to be enough water to push all the salts down,” Diener said.

As a result, salinity stays higher in drip systems, which limits the types of crops farmers can grow.

In one of Diener’s fields, after drip irrigating for four years straight, he had to use 15 tons of gypsum to flush out the salts from the soil.

“With pivot irrigation, you use maybe one or two tons of gyp every couple of years,” he said.

With higher quality soil on his pivot irrigation fields, Diener has more options to grow higher quality crops such as lettuce, beans, onions and garlic on land that, with the drip system, might otherwise have had too much salinity.

While Diener has had good success with pivot with his corn, alfalfa and sugar beet crops, tomatoes are more of a challenge. As soon as the fruit turns pink, he has to water his tomatoes with the overhead system without actually getting the fruit wet.

The solution for this, Hanshew said, is to drag pieces of hose from the overhead system along the insides of the furrows

“We replace the regular sprinkler drops with hoses that get dragged inside the furrows as soon as we see the first pinking of the tomatoes,” Hanshew said. “That’s important because we know the tomatoes get susceptible to bacteria and viruses.”

The one big drawback with pivot irrigation, many growers say, is that the system works best in circular fields. Growers end up losing about 22 percent of their acreage when they convert their square fields to circles.

“But then again, that’s 22 percent less water we’re using,” Diener said. “And that may be just as well, since our water allotments are getting cut back and we might not have enough water to farm all the land we have anyway.”

– Lisa Lieberman