When operating center pivot irrigation, uniformity is the name of the game. "Lack of uniformity costs bushels," Derrel Martin, University of Nebraska Extension irrigation and water resources engineering specialist, told a group of producers at the UNL center pivot shortcourse in O'Neill recently.
Having the right system capacity, correct pressure and nozzle package and spacing are contributing factors to uniformity in the field. "The system capacity should be large enough to meet the crop water use rates most of the time, while not being so large that they contribute to runoff issues," Martin said.
Outer spans of a pivot irrigate more area, so they must discharge more water than inner spans. In fact, on a typical seven-span system, the sixth and seventh outer spans cover about 45% of the total irrigated area under that pivot, and distribute 45% of the total system flow.
"If you don't have correct pressure, you are not operating efficiently," Martin said. Pressure at specific nozzles along the system depends on the pressure at the pivot inlet, the change of elevation at any point along the pivot compared to pressure at the inlet, and loss of pressure along the way due to friction. So, pressure at the pivot end is usually lowest when that end is on the highest point in the field.
"Poor uniformity results in yield loss in the middle rows and runoff between the sprinklers," Martin said. He suggested purchasing pressure gauges for the inlet end and the outer end of the pivot, to make sure the system is operating at peak efficiency.
"The sprinkler and the nozzles are the heart of a pivot," Martin explained. If the sprinkler spacing is right, the system provides equal opportunity to water all the crop rows. He said that there should be adequate overlap, so all plants are guaranteed to receive the same amount of water.
Farmers might be tempted to reduce their costs by spacing sprinkler nozzles farther apart than is recommended, but Martin said that this costs money in the long run in lost potential yield.
You can learn more about improving center pivot uniformity by contacting Martin at 402-472-1586 or email [email protected].