So it's man-made. Confirmed in an episode of National Geographic. They can do it overnight. They check for radiation emissions on crop circles but found little to none, so a machine from a UFO is not present to create them, and also confirmed that the UFO sightings on the areas were fake.

Plus some videos and photos were fake...but the amusing variability of the complex designs makes it curious for us to watch how it was made.

"Everything in this book may be wrong." Illusions: The Adventures of The Reluctant Messiah by Richard Bach