What is in this article?:
Overhead irrigation systems combined with conservation tillage is an exciting melding of technology and production agriculture.
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.