A severe geomagnetic storm that hit the Earth over the weekend disrupted the work of many farmers in the U.S.

A geomagnetic storm is a disturbance in the Earth’s magnetosphere caused by particles from the Sun. The weekend’s event was caused by a series of phenomena known as coronal mass ejections, or CMEs for short. A CME is a burst of plasma from the outer part of the Sun’s atmosphere, or corona, that can reach the Earth at speeds exceeding 1,800 miles per second.

The U.S. National Oceanic and Atmospheric Administration began issuing warnings about unusual solar activity late last week. On Friday, the agency observed more than a half dozen CMEs emerging from the Sun. Two days later, on Sunday, the plasma bursts reached the Earth and set off a geomagnetic storm that was given a rating of G5, the highest possible severity grade.

Geomagnetic storms can disrupt several kinds of navigation and communications equipment. That includes the autonomous navigation hardware of some tractors, the Times reported. The disruption left many U.S. farmers unable to plant corn with their John Deere vehicles.

The affected tractors use an autonomous navigation system to identify the optional way of placing seeds in the ground. This navigation system makes driving decisions based on GPS data, as well as a so-called RTK device that is responsible for correcting errors in GPS signals. This RTK or real-time kinematic positioning device enables tractors to plant crops with centimeter-level accuracy. 

The Sunday storm in the Earth’s magnetic field interfered with many John Deere vehicles’ RTK equipment, which forced farmers to pause their work. Without a functioning RTK device, a tractor can’t accurately follow its preprogrammed travel path and may consequently plant seeds unevenly. That leads to unusual crop placements, which can make harvesting difficult or impossible down the road.

“When you head back into these fields to side dress, spray, cultivate, harvest, etc. over the next several months, we expect that the rows won’t be where the AutoPath lines think they are,” LandMark Implement Inc., the operator of several John Deere dealerships, cautioned in a Saturday statement. “This will only affect the fields that are planted during times of reduced accuracy.”

The disturbance in the magnetosphere affected not only tractors but also certain other systems. Users of Starlink, SpaceX Corp.’s satellite internet service, experienced intermittent outages over the weekend. 

NOAA determined that the geomagnetic storm was the most severe since 2003, when a burst of solar plasma caused a power outage in Sweden. In 1987, a similar solar disturbance left residents of Quebec without electricity for several hours.

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