On the radio, ongoing saga that's produced by farmers (6)
I believe the answer is:
cereal
'that's produced by farmers' is the definition.
(food product which is farmed)
'on the radio ongoing saga' is the wordplay.
'on the radio' shows a homophone (sound like).
'ongoing saga' becomes 'serial' (eg a TV serial).
'serial' sounds like 'CEREAL'.
(Other definitions for cereal that I've seen before include "Rye, for example" , "Something for brekkie" , "Breakfast dish" , "Eg, wheat, rye, corn" , "Food prepared from grain" .)