Working Ranch Magazine January/February 2025

pasture management BY LORETTA SORENSEN

discuss issues in producer fields. We also present procedures for selecting sprinkler packages and a checklist of things that can help ensure that the system is operating efficiently.” UNL’s handbook describes a typical center pivot as a seven-span pivot with span widths of 180 feet and a 50-foot overhang at the end of the pivot lat eral. The pivot in their diagram “irri gates 124 acres when there is no end gun. Since the spans at the distal end of the system travel much farther per revolution of the pivot, the outer spans irrigate much more area than spans of the same length at the center of the field. Because the outer spans irrigate more area, they also must discharge more water than inner spans.” For the system described here, “about 45% of the irrigated area is located under the 6th and 7th spans of the system, and correspondingly, 45% of the total system flow is distributed from the 6th and 7th spans. 24% of the land area and 24% of the system discharge are associated with the last span. If sprinklers are spaced at the same distance along the lateral, the sprinklers on the outer spans must discharge more water than sprinklers located nearer the pivot point.” The publication explains that installing the correct type of sprin klers and nozzles at the proper loca tion along the pivot pipeline is vital to the pivot’s operation. The producer must know the pivot system’s capac ity to select appropriate nozzles. The secret to proper design and installation lies in determining the following: • Discharge needed for each sprin kler along the lateral. • Pressure available at each sprinkler. • The required size of nozzle needed in each successive sprinkler to meet the discharge requirement. CAPACITY CALCULATIONS System capacity is determined using the flow ratio into the pivot divided by the amount of land irrigated.

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A Pivotal Moment Understanding is the key. any rancher’s rely on irrigation, which is why it’s important to understand the finer details of how a pivot works, allowing you to identify potential issues before you leave the ranch (which we all know is when water issues are bound to happen.) For those of you who haven’t gotten your hands on the The Department of Biological Systems Engineering at the University of Nebraska-Lincoln (UNL) 2018 136 page “Center Pivot Irrigation Handbook” we’re highlighting some things you should know before turning on the pump.

irrigation equipment. The Department of Biological Systems Engineering at the University of Nebraska-Lincoln (UNL) 2018 136-page “Center Pivot Irrigation Handbook” notes that “cen ter pivot irrigation has been the most rapidly expanding form of irrigation in the Central Great Plains and across the United States.” This PDF document is available as a free download at https:// extensionpubs.unl.edu/publication/ ec3017/center-pivot-irrigation-hand book-ec3017 or by searching “Center Pivot Irrigation Handbook ec3017.” “With the widespread use of pivots, it is important to provide techniques to evaluate if pivots are operating as designed and to develop methods to identify issues in producer fields,” the UNL publication states. “In this document, we describe the design procedure for center pivots to illus trate how pivots should operate and

The October 2024 USDA National Agricultural Statistics Service (NASS) reported that their 2023 Irrigation and Water Management Survey data indi cated that “equipment, in general, is one of the leading irrigation expendi tures with farmers and ranchers spend ing $3 billion on irrigation equipment, facilities, land improvements, and computer technology in 2023; energy costs for pumping well and surface water amounted to $3.3 billion.” NASS also reported that “farmers irrigated 49.6 million acres of harvested crop land in 2023. Five states accounted for around one-half of the irrigated acres, and more than half of all water applied – Arkansas, California, Idaho, Nebraska, and Texas.” This survey data was gathered from approximately 35,000 producers who indicated in the 2022 Census of Agriculture that they irrigated or had

34 I JANUARY / FEBRUARY 2025 WORKING RANCH audited readers run 21 million head of beef cattle.