Posted 26 September 2014. PMN Crop News.
Pivot Irrigation, Not Furrows, is Most Economical for Delta
Source: Mississippi State University Press Release. www.cals.msstate.edu
Stoneville, Mississippi (September 5, 2014)--Pivot irrigation is no longer a common sight across the Delta, but experts say this system remains a viable and efficient way to water crops.
“I would like to see pivots in the Delta,” said Jason Krutz, irrigation specialist with the Mississippi State University Extension Service. “They deliver water more efficiently, so if we have an aquifer problem, which everything indicates we do, they would go a long way towards helping address it.”
In recent years, Delta producers have been removing pivot irrigation from their farmland and replacing it with furrow-irrigation systems after their fields were land-formed. Most pivot systems in the Delta were installed 25 to 30 years ago and were designed to conservatively meet the estimated daily water needs of cotton.
More recently, pivots have been designed to meet the maximum daily water requirements of all crops grown in the Delta under the most extreme weather conditions.
“Many producers have a pivot on one field and furrow irrigation in an adjacent field, and they have a higher yield in the field with furrow irrigation,” Krutz said. “They have higher yields because furrow irrigation can keep up with the water demands of cotton, but these older pivots were not set up to keep up with the maximum water demands of corn and soybeans.”
Spray nozzles on pivots can be checked and replaced, and the entire system can be revamped to provide a higher rate of water. Cost-share packages are available to help producers make this happen, but in the Delta, many choose to abandon this method of overhead irrigation.
Krutz would like to see this trend reversed.
“Furrow irrigation is about 55 percent efficient, which means for every inch of water I apply, only one-half reaches the target, which is below the soil surface but not deeper than 3 feet,” he said. “Pivots are about 85 to 90 percent efficient, so for every inch of water, almost nine-tenths of an inch reaches the rooting zone.”
Furrow irrigation uses a collapsible pipe with holes punched in it. A pipe placed in each row allows water to flow down the furrows. While polypipe is not expensive, and maintenance is simple, the ground may need to be sloped so that water flows across the entire field.
This dirt work can make the cost of setting up furrow irrigation as expensive as the cost of installing a pivot-irrigation system.
Larry Falconer, Extension agricultural economist at the MSU Delta Research and Extension Center in Stoneville, has included these costs in planning budgets available to producers.
“In some cases, the dirt work can exceed the cost of the pivot equipment,” Falconer said. “We calculated that installing a half-mile pivot costs about $400 per irrigated acre. If you assume it will cost $1.35 per cubic yard for dirt work, installing furrow irrigation will be more expensive than installing pivot irrigation if you have to move more than 350-400 yards per acre.”
Falconer said installation costs for pivot irrigation is lowest on square fields, but furrow irrigation is better suited for irregularly shaped fields.
It also costs less to operate pivot irrigation than to furrow irrigate.
“If you start with a half-mile pivot-irrigation system, total costs to irrigate with 7.5 inches of water per acre are just under $99 an acre,” Falconer said. “A comparable rollout pipe system would use 13 inches of water per acre and have a total cost of $105 per acre. You’d be pumping about 60 percent more water because the furrow system is less efficient.”
Lyle Pringle, associate agricultural engineer and irrigation researcher with the Mississippi Agricultural and Forestry Experiment Station, explained the efficiency losses in both systems.
“You have to put on more water with furrow irrigation because it has to run from the upper end of the field to the bottom end of the field,” Pringle said. “To get a good irrigation on the bottom third of the field on a lot of our soils, you have to run some water off to give more time for water to soak in on the bottom. You don’t have that much runoff with a pivot.”
Pivot irrigation sprays water over the tops of the plants, and some is lost to evaporation. With furrow irrigation, some is lost into the soil as the water percolates deeper than the rooting zones. But furrow irrigation has some benefits.
“With furrow irrigation, you can water every acre,” Pringle said. “With a pivot, you generally have to leave out the corners. Since most systems are electrical, when pivot systems go down, they can be more difficult to fix and they can get stuck in the field. Downtime needs to be minimized with pivots, because they are not designed to play catch-up.”
Pringle would like to see existing, older pivots renozzled to more efficiently meet the needs of crops during the highest water demand. Wells should be designed and maintained to deliver the designed flow for the life of the system.
“I believe a well-managed, well-designed pivot can make just as much yield as a furrow,” he said. “Furrow irrigation efficiencies can be improved with better water management, but inherently will be less than a well-maintained pivot system. And as water continues to be pumped from the aquifer and we have less and less in reserve, pivots make good sense.”