The coupling of overhead, mechanized irrigation systems with conservation tillage has resulted in the most exciting melding of technology and production agriculture Jeff Mitchell has seen in his University of California career.

Mitchell, cropping systems specialist in the plant sciences department, persistently has researched and demonstrated for at least a decade in an attempt to make pure, no-till farming part of California agriculture. It has been a struggle, although he has gained followers among some of the leading San Joaquin Valley farmers.

Long before Mitchell began preaching his no-till gospel, California farmers had reduced tillage, albeit slowly, largely for cost savings. They had done it with implements that performed several tasks in one pass. They had done it by adapting tillage equipment designed for drip irrigated farming.

Drip or micro-irrigation, introduced into California in 1975, has reduced tillage greatly in trees and vines, since furrow irrigation was replaced by low volume drip.

Drip has also made huge inroads into field crops, primarily for high value crops like tomatoes and vegetables, again minimizing the need to cultivate as much with furrow or check irrigation.

One of the biggest roadblocks to reducing tillage on row crops like wheat, corn, cotton, and alfalfa is the need to control irrigation water with beds or checks. Several years ago Monsanto made a major effort to get growers to switch to no-till with Roundup Ready cotton. It did not work since cotton requires beds to control water and cultivation to manage irrigation water. Growers readily adopted the herbicide-resistant biotechnology, but not no-till farming.

However, new fundamentals have befallen California agriculture that are forcing the new paradigm Mitchell talks about. The costs and availability of labor and water are forcing growers to become more efficient than ever in field crops.

Enter overhead mechanical irrigation. It, Mitchell says, offers “tremendous potential” of coupling conservation tillage with mechanized pivot or lateral irrigation, while reducing water use at the same time. There are no furrows or beds with overhead irrigation.

Mitchell made his observations at a symposium sponsored by Valmont Irrigation during World Ag Expo.

Mechanical, overhead irrigation systems date to the 1950s and were introduced into California then. Pivots and linear irrigation systems have been used since, but have never been a major irrigation technique, primarily because they could not be adapted to California’s heavy and irregular soil types.

Early overhead drawbacks gone

Those and other early-day drawbacks are gone, as reflected in a presentation by Dan Wilke of Bolthouse Farms based in Bakersfield, Calif. Bolthouse is one of the leading carrot producers in the U.S.

Bolthouse carrots have been grown for years with solid set sprinklers in sets of six, 10 or 12 hours. Switching to pivots represented a major change in irrigation management and mindset.

“Center pivots are a lot like micro-irrigation. You do not want to get behind on irrigation. However, if you do get behind, you can catch up with the flexibility of a pivot,” said Wilke.

Bolthouse experimented with three pivots in 2005 and made the decision to switch completely from solid set sprinklers to pivot in 2006. “But when you change to pivots, you have to make a commitment to make it work. People do not like change.”

The early day problems of matching pivot water application rates to soil infiltration rates have been resolved. Infiltration rate is the quantity of water that can enter the soil in a specified time interval.

Growers, said Wilke, can match the two, but it requires plenty of soil sampling to match sprinkler packages with soil types. Operation flexibility of a pivot also allows growers to vary the rate of travel to compensate for different soil types.

When irrigating through solid set sprinklers, irrigation is measured in set times. With pivots it’s “instantaneous application rates. It is an easy term to explain, but difficult to understand,” said Wilke. Instantaneous application rate (IAR) is the peak intensity of water application at a point, according to Nelson Irrigation, one of the leading supplies of nozzles for center pivots.

Bolthouse uses at least three sprinkler packages on each pivot to match the flow rate to the soil infiltration rate. Some have four sprinkler packages to match soils. Since carrots are a small seeded plant, Wilke says droplet size is also critical to germinating small seeded carrots. Bolthouse does not want compaction from large droplets or runoff.

He employs twin-span pivots capable of putting out a total of 1,500 gallons per minute (750 gallons per minute per side). They operate 180 degrees opposite in the field. They can irrigate 135 acres with a tenth of an inch of water every 2.5 hours.

Tracking issues are resolved with three-wheel base towers and “boom back” structures that position sprinklers behind the wheels so they will not get bogged down.

They are operated manually from the control box or by telemetry from pivots to computer base stations. These base stations not only tell Wilke and his crew which pivots are operating where, they also tell the operator wind speed, soil moisture levels and other important data. Some irrigators have laptops that allow them to access the same information.

Pivot success

Wilke says Bolthouse has experienced a 30 percent reduction in water use with the pivots along with improved carrot quality. “When you use less water, you use less fertilizer and pesticides,” he said. Many of the nutrients and pesticides are applied through the pivots, reducing tractor and aerial application costs.

With pivots, Bolthouse has parked pipe-hauling trailers and trucks and the maintenance cost of that equipment. And no more leaky gaskets — a common malady of portable solid set. “You may lose productive ground with a pivot, but when you put it all together, you save more on the other side and get more yields per acre and better quality.”

Reduced water use is attributable to improved application water uniformity with pivots. Mitchell said catch-can experiments and refined irrigation sprinkler packages have achieved a 93 percent uniformity rate.

Mitchell said overhead sprinklers eliminate the need for beds and irrigation checks, playing right into conservation tillage where crops can be planted directly into previous crop residue without major tillage.

“Five years ago we had no center pivots on the West Side of the San Joaquin Valley,” said Mitchell. Now there are dozens. “It is still small, but with the dwindling water supply and the shortage of reliable labor the number will grow.”

He does not believe the water crisis will go away. He points to the Oglala Aquifer in the Midwest and Texas where severely depleted groundwater supplies limit the amount of water farmers can legally pump.

So far there are no groundwater pumping restrictions in California’s agricultural areas. However, many believe that day is coming to an end, which will only further limit water supplies.

The resurgence of interest in center pivots in the West has the USDA-NRCS office considering a public demonstration plot to encourage growers to switch, according to Chris Hartly, from the Stanislaus County NRCS office.

NRCS has $40 million available in EQIP conservation money to support water conservation improvements, like center pivots, by cost sharing with growers.

He said NRCS could pick up as much as half the cost of a $100,000 pivot.

hcline@farmpress.com