She was joined by actors Tim Bentnick, who plays David Archer, David Troughton, who stars as Tony Archer, and Susie Riddell, who appears as Tracy Horrobin.
“Nerves are frayed on the day of the Borchester Show, and a surprise guest makes their mark,” the programme’s website had hinted.
The duchess was following in the footsteps of Queen Camilla, who appeared on the soap in 2011.
The Queen, also a self-confessed Archers addict, acted out her role as president of the National Osteoporosis Society, in a special episode to mark The Archers’ 60th anniversary.
Queen Elizabeth II’s sister Princess Margaret also made a cameo in 1984, when she was a surprise guest at a fundraising fashion show for the NSPCC, in the ballroom of Ambridge’s local hotel Grey Gables.