It is a specific form of irrigation know as Center Pivot Irrigation
Fairly simply explained on Wikipedia
Center-pivot irrigation (sometimes called central pivot irrigation), also called waterwheel and circle irrigation, is a method of crop irrigation in which equipment rotates around a pivot and crops are watered with sprinklers. A circular area centered on the pivot is irrigated, often creating a circular pattern in crops when viewed from above (sometimes referred to as crop circles). Most center pivots were initially water-powered, and today most are propelled by electric motors.
No crazy alien landings here!
Credit:stackoverflow.com‘