What is in this article?:
- Is it time for a center pivot revival in the Delta?
- System 'right on target'
- NRCS financial assistance available
Many center pivot irrigation systems in the Delta are 25 years old or more. Based on their experience with these systems, some growers have a perception that center pivots can’t keep up with crop water demand and are converting to surface irrigation. “It’s a disturbing trend,” says Paul Rodrigue, USDA National Resource Conservation Service supervisory engineer at Grenada, Miss. “These conversions reduce irrigation efficiency and increase demand on already stressed groundwater resources.”
DISTRIBUTION of water from an appropriately configured modern pivot system can be more water-efficient than surface irrigation, a NRCS study demonstrates.
System 'right on target'
“From these measurements and the measured radius of the last tower, we calculated that the pivot would complete one full circle in 3.1 days,” Rodrigue says. “Once the pivot had sufficiently passed all the catch rain gauges, the system was stopped and application depths read. The average measured application was 0.71 inch. That calculates to a pivot capacity of 0.23 inch per day.
“Traditional irrigation design in the Delta aims for an irrigation rate of 0.25 inches per day, so the system was right on target. With today’s crops and variety potential, and the extremely dry conditions in recent growing seasons, some producers are moving toward an 0.30 inch per day capacity.”
The application rate rain gauge captured 0.77 inches over approximately 22 minutes, he says, giving an average application rate of 2.11 inches per hour.
“That rate is much more in line with the intake rate of many Delta soils,” he says, “and is lower than many of the measurements of 25 years ago. This rate could have been even lower with the alternating truss mounting.”
The pivot was not equipped with a flow meter, he notes, so system efficiency couldn’t be evaluated, “but with the newer nozzle spray patterns and drops, a high efficiency would be expected.”
NRCS provides financial assistance for flow meters.
While this evaluation was for only one newer center pivot system, Rodrigue says “It is evident that the new nozzles, new system designs, lower operating pressures, and drops can provide a system with high irrigation efficiency, while meeting crop needs and soil limitations. Furrow diking could also aid water infiltration.
“With the addition of a soil moisture sensor, initiation of pivot irrigation can be more efficiently managed to insure that soil moisture isn’t depleted too much before irrigation begins.”
NRCS offers financial assistance for re-nozzling and adding drops to older systems, he notes, and can also assist in replacing old high pressure pivots with newer low pressure models.