The last tasks of center pivot irrigation

The bittersweet of late fall is here. Once again, the growing season is in the books and the last of the crops are being harvested. 

The declining temperatures indicate it is time to prepare equipment for winter. In the scramble of tasks needing to be accomplished before winter slams home, don’t forget to take time to assess and winterize center pivots.

Winterizing a pivot can be as simple as pulling plugs and draining water from all pumps and pipes. However, this is an appropriate time to do a thorough inspection of the entire irrigation system.

Conducting a thorough inspection in the fall provides a fully serviced and functional pivot for the next spring, it allows time for ordering parts, correctly repairing issues and operators are more likely to remember the issues from the previous growing season needing to be addressed.  

Winter preparation 

A complete inspection and winterization process starts with assessing the uniformity of the sprinkler package prior to shutting the system down. This is done by setting cups or rain gauges in a straight line from the pivot point to the reach of the end gun, then running the pivot over this line and recording the water collected per cup. 

This test indicates if a few nozzles or the complete sprinkler package needs replaced. Contact a local Extension office or e-mail jvardima@uwyo.edu for a publication detailing this procedure along with considerations. 

While running the uniformity test, check for leaks, malfunctioning or missing sprinklers, leaking gaskets, damaged pipes, etc. Of course, these issues will affect the data collected during the uniformity tests and should be repaired for accurate data for the sprinkler package. 

Prior to shutting off a center pivot which utilizes an irrigation well and has iron bacteria present, well maintenance should be considered and conducted annually. If the well screen, casing and pumps are covered in a slimy gelatinous mass, the irrigation equipment has a rust color or the water has a rotten egg smell, then iron bacteria is a good possibility in the well. 

The only effective way to control bacteria is by chlorinating the well at least once a year. Remember, chlorine is a noxious and dangerous gas and can be explosive if it mixes with oil found in the top of water in wells, typically found with oil-lubricated deep well turbine pumps. It is recommended to use common household bleach (unscented) because it is the safest form and readily available.

Chlorinating wells 

Chlorination of the well should be done prior to winterizing pipelines. Contact a local well company or local Extension office for information on the amount of chlorine required and procedures for chlorinating a specific well. 

Chlorine needs to be at appropriate concentration levels and let stand in the well for 24 hours for it to be effective. Remember, chlorine is very corrosive to iron, so do not let the chlorine stay in the well or pipes throughout the winter. Chlorinating the well will keep the production similar to when it was first drilled.

After the uniformity test and chlorination has been conducted, it’s recommended to park the pivot into or with the prevailing wind to prevent storms from flipping the pivot. Once parked in the desired position, shut down and lock out the power supply so the irrigation system cannot be turned on to pump water during freezing temperatures. 

Other considerations

Remove plugs to drain all pipes, valves, pumps, pressure gauges, end gun systems and anything else above ground which can hold water. After water has been drained, open all valves to the half open position. 

Service all engines operating pumps, pivot tower gearboxes, drive lines and center drive motors by draining water from these items and filling oil to appropriate levels or conduct a complete oil change. Oil in gearboxes should be replaced every three to five years depending on the hours of use. 

Check and maintain tire pressure at recommended levels, even going into the winter. In addition, lubricate all fittings, bearings and shafts. Also, loosen any belts or packing glands if they are used. 

Clean electrical contacts with a contact cleaner to prevent corrosion. This includes checking microswitches in the tower boxes for bee activity interfering with their function. This is especially true for areas with leafcutter bees which are typically found around alfalfa seed production.

Close all openings on the system which might invite rodents or birds to use. An example of this, which many do not think of, is replacing the sand trap plug at the end of the pivot so birds do not utilize or build nests inside the pipe. It is recommended to fence livestock away from engines, pumps and the pivot pad to keep livestock from damaging any components. 

Lastly, record the end readings for flow meters and system panels, and include any notes from the servicing for records. Record any parts to order and repair. 

Conducting this complete inspection and winterization process provides the best conditions for the irrigation system to tolerate the weather and fluctuating temperatures between fall and next spring. It also provides a fully serviced and functional pivot ready to be utilized next spring in addition to saving valuable workdays in the spring.

Jeremiah Vardiman is a University of Wyoming Extension educator. He can be reached at jvardima@uwyo.edu.