Jimmy visits the USA, the greatest food-producing country on earth. The farmers have put their faith in new technology to increase food output, but is it enough? In search of answers he visits the tomato fields and bioscience labs of California, a high-output pig farm in Iowa, and gets a taste of the Wild West while herding buffalo in South Dakota. Yet it's a farm in North Carolina that offers the most surprising approach of all.

• Jimmy Doherty