Nearly 90% of the 8-1/2 million irrigated acres in Nebraska is watered by center pivot systems. That's a remarkable changeover in how water is delivered to crops, considering that just 20 to 25 years ago gated-pipe and other gravity-flow systems accounted for about half of the irrigated acres.
Statistics on pivot numbers in Nebraska haven't been updated for several years, but it's estimated there are 60,000 or more systems in the state. That number may be a conservative.
But while pivots generally are considered to be 85 to 90% efficient in applying water, not all systems meet that objective. With that in mind, University of Nebraska-Lincoln specialists and representatives of the four Nebraska-based center-pivot manufactures four years ago formed a partnership called the Center Pivot Water Conservation Project.
Derrel Martin, UNL irrigation/water resources specialist, says the purpose of the partnership and a series of meetings with farmers and dealers was to "maximize the benefit of a constrained water supply and to help center pivot irrigators apply water more efficiently." A Nebraska Environmental Trust grant supported the project.
Out of that effort came the "Center Pivot Irrigation Management Handbook," 134-page publication that soon will be available, in hard copy and online. Final editing changes were being made as this went to press.
When it is finished, go to the UNL web site http//:water.unl.edu, and click on "Agricultural Irrigation" where you can find instructions on ordering the book.
There are 10 chapters in this comprehensive evaluation of pivots, their design and operation.
In the handbook's introductory chapter, authors say: "In this document, we describe the design procedure for center pivots to illustrate how they should operate and discuss issues in center pivot performance that we are observing in producer fields. We also present procedures for selecting sprinkler packages and a checklist of things that can help insure that the system is operating efficiently."
Here's a review of the content of each chapter:
Chapter 1, introduction.
Chapter 2, center pivot performance, including system pressure, system capacity, nozzle size and flow rate.
Chapter 3, soil water management, including infiltration and soil moisture measuring and soil measuring
Chapter 4, Pivot sprinkler packages, including sprinkler types, height and spacing.
Chapter 5, irrigation pumping plants and pumping plant performance.
Chapter 6, energy use in irrigation, including energy requirements, costs and pumping plant efficiency
Chapter 7, Crop water use, including calculating evapotranspiration.
Chapter 8, Water resource management, with information on watersheds, consumptive use, recharge and runoff.
Chapter 9, limited irrigation practices.
Chapter 10, Center pivot management issues, including sprinkler installation and maintenance problems, system pressure problems, practices to reduce runoff and a checklist of maintenance and management activities.