Pengelly Farms of Cornwall was fined £75,000 and ordered to pay £50,000 costs following the fatal electrocution of worker Konrad Miskiewicz in July 2011.
Truro Crown Court heard the 24-year-old Pole was working behind a harvester which came into contact with overhead power lines while being reversed down a field which the company rented.
Pengelly was investigated after the incident and prosecuted by the Health and Safety Executive (HSE), having earlier pleaded guilty to a breach of the Health and Safety at Work etc Act 1974.
And Staffordshire grower W B Daw & Son was fined £15,000 and ordered to pay costs of £25,000 after another Polish worker, Marek Wasilewski, lost an arm which became caught in the rollers of a potato grading machine he was cleaning in November 2013.
An HSE investigation found found unsafe systems of work being used, including cleaning and clearing blockages from the rollers while they were still rotating under power.
HSE Inspector David Brassington said: "This incident could have easily been avoided had the machine been switched off and securely isolated before cleaning work started. But W B Daw & Son had failed to give clear instructions to its employees and failed to monitor their activities."