If I had to go back to row water (furrow irrigation), I wouldn’t be farming today,” says Doug Dunlap, who credits center pivots with helping to keep him in business in arid Arizona.
Dunlap, a fourth-generation crops farmer, owns Dunlap Farms in the Sulphur Springs Valley at Willcox in southeastern Arizona, an area bordering New Mexico and Mexico.
Dunlap and his brother, Darren, who operate separate farms, grow 4,500 acres of alfalfa, pinto beans, chile, corn, and milo in the high desert at 4,400 feet above sea level in Cochise County.
The farm fields are shadowed to the north by the picturesque Pinaleño Mountains and the Winchester range to the west.
Dunlap farms in 160-acre crop circles (one-quarter section), which allows crop production on 120-125 acres in the circle. The mountainous terrain can drop 20 feet from one end of a circle to the other.
Wells and rain are the main water sources. Most well water is pumped from a depth of 300 to 400 feet. The area averages 7 to 10 inches of rain annually.
Soil types vary across Dunlap’s fields, from a Tubac sandy loam and Tubac clay loam on the north side of the farm near Bonita to a sandy Pima loam closer to Willcox. Center pivots allow him to adjust the irrigation based on rainfall and the various soil types.
The Dunlap family is among an entourage of farmers who brought their center pivot experience from West Texas in the late 1960s to this mostly row water (furrow and other types) irrigated Arizona community.
One of the first changes the Dunlaps made was to switch from row water to center pivots.
“Today, it would require about 20 irrigators and 20 pickup trucks to irrigate this farm with row water, including turning the water on and off,” he says. “The labor savings with center pivots are huge.
“Pivots irrigate the ground more evenly; row water irrigated unevenly, especially near the lower levels in the field.”
The bottom line: center pivot technology allows Dunlap to farm more efficiently and effectively. He estimates his water efficiency at about 90 percent.
Original pivot systems were designed for hilly ground that could not be row watered, he says. The systems had high impact nozzles, with 50 to 60 pounds of pressure per square inch (PSI), which increased soil compaction. Modern pivot systems can deliver 15 to 30 PSI.
Another change in pivot use in the Willcox area was placing the irrigation drop hoses closer to the ground. Today, drops are often 30 to 60 inches apart and hang two to three feet from the ground.
In corn, Dunlap places the drops 20 inches from the ground, which provides improved water delivery to the plants with less evaporation.
He uses Nelson and Senniger nozzles. Smooth spray pad nozzles break up the water into a fine mist for soils to better absorb water. A corrugated pad with large droplets is used on heavier soils.
Dunlap, who is proficient in center pivot technology, operates High Desert Irrigation, a Valley Irrigation dealership.
“We figured out years ago that, with center pivots, we make just as much money farming 120 acres as we would 160 acres, due to fewer expenses and reduced water use,” he says.
Pivot irrigation works better than row water on all of his crops. Depending on rainfall, his average for a pivot-fed corn crop is 24-30 inches of water annually, 36-38 inches for alfalfa hay, 20-22 inches for milo, 24 inches for chile, and 18-20 inches for pinto beans.
Center pivot efficiency
Dunlap says center pivot use in his area boils down to efficiencies — which keeps more money in the grower’s wallet.
“I get more uniformity with pivots versus row water. My crop yields are 15 percent to 20 percent higher with pivot irrigation.”
Pivots also allow him to utilize minimum tillage.
“With row water, we had to get the land black, landplane it, and list it, which meant a lot of trips across the field,” Dunlap says. “Now, we can disk the ground a couple of times and then plant corn.”
An installed quarter-mile-long center pivot system costs about $70,000 on average, he says.
The pivot’s speed is adjustable. A 16-hour complete circle applies about three-tenths inch of water.
Some herbicides, fungicides, and pesticides are chemigated through the pivot system, which is particularly effective on Dunlap’s chile crop.
“I can apply water that includes a pesticide to kill nematodes in the chile,” he says.
Center pivot irrigation is slowly gaining in popularity in the West. Acceptance has been slow for a number of reasons.
“A lot of land in the West is high dollar land, where growers don’t want to leave land out of production (the circle corners),” Dunlap says.
“The cost of the center pivot is probably another factor, and the technology is still new to some people. But, the technology in new pivot systems is easy to operate.”
Early problems with center pivots in the U.S. included tires becoming stuck in wet ground. Farmers in Cochise County have learned ways around that, including planting cover crops and utilizing minimum tillage instead of ripping the ground.
Drip irrigation is also catching on in the West, but Dunlap says it is not a good fit for his area due to the large numbers of gophers and mice that chew on drip tape.
Robert Call, University of Arizona area horticulture agent for Cochise County, says the Willcox area has about 500 center pivot systems, which irrigate about 90 percent of the county’s crop acreage.
Pivot system water efficiency ranges from 80 percent to 90 percent, depending on the system setup and soil conditions, Call says. Systems can be automated and controlled by cell phone or computer.
“The efficiency factor depends on the drops, plus crop canopy height, wind, and cloud cover,” he says. “During the summer monsoon (rainy) season, the sky can be cloudy until sunset.”
Call says center pivots are adaptable to small grains, corn, hay, and other crops popular in the area.
Edward Martin, irrigation specialist, University of Arizona, Tucson, says, “One advantage that growers in Cochise County have is that most center pivot systems are fairly new and incorporate the latest technology. One person can manage several hundred acres at a time.”