It was the largest public gathering – with some 20,000 visitors – the couple have walked among since the pandemic started.
Charles appeared engrossed in the show ring, inspecting prize-winning cattle and, later, sheep.
And it was during a chat with South Devon cattle judge Anne Tully that he trod in a fresh cow pat.
Mrs Tully, from Brixham, Devon said afterwards: “I told him that was luck, that’s what we always say.”
The prince then came face to face with champion 1,550kg Hereford bull Moralee One Rebel Kicks, owned by Tom and Di Harrison from Stocksfield, Northumberland.
Mr Harrison said afterwards: “I could have talked to him for an hour.
“He is very knowledgeable and I would have liked to have bought him a pint.”
Charles looked happy to stop and chat to visitors during his three-hour tour of the huge site.
He spoke to Hannah Richardson, from Ripon, who brought her eight-month-old baby Phoebe to the show.
Afterwards, Mrs Richardson said: “I can’t believe she has met the prince – this is the first big event she has been to because of lockdown.”
And Charles was given a warm welcome by horse trader and father-of-six Red Lee Smith, who spotted the prince and gave him a booming hello as he walked by.
The gypsy from Dublin is currently staying in Doncaster, South Yorkshire, and told Charles he was visiting the show with his family.
After asking: “Can I get a photo with Mr Charles?” Mr Smith told the prince: “You’re looking well.”
Charles replied: “Not too bad yourself.”
As they parted Mr Smith wished him “God bless”.
Afterwards, Mr Smith said: “He’s all right. I’ve met him before. I’ve met Harry a few times too.”
The prince stopped for selfies with some groups and chatted to fruit seller Ollie Fuller, who gave him a punnet of strawberries from Thirsk, North Yorkshire.
The event did not happen last year and Mr Fuller said: “It was great to see him, it’s great to be back.”
The prince talked to farmers throughout the visit and was pleased to launch a new guide to help them go green, which aims to demystify some of the jargon which surrounds environmental agriculture methods.
The guide, which was Charles’s idea, came from the Prince’s Countryside Fund, supported by McDonalds.
In a speech, Charles said: “It is unhelpful that many terms used to describe environmental processes are somewhat obscure and off-putting.”
He added: “Once we all understood what we need to do, of course the next step is to go on and do it.”
He hoped the A-Zero guide would help farmers achieve that.
The Duchess of Cornwall toured the show site separately from her husband for most of the afternoon and held a hedgehog, calling it a “happy hog”.
She also met children, held a spider and some baby owls.
Camilla met Deb Howe, who was balancing a chicken on her head, from Eggucation – an organisation which teaches schoolchildren about ethical chick-hatching projects.