Ferret cut farmer's production in field (4,4)

I believe the answer is:

root crop

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'farmer's production in field' is the definition.
(crop whose roots are eaten)

'ferret cut' is the wordplay.
'ferret' becomes 'root' (I am not sure about this - if you are sure you should believe this answer much more).
'cut' becomes 'crop' (cropping is a kind of cutting).
'root'+'crop'='ROOT CROP'

Can you help me to learn more?

(Other definitions for root crop that I've seen before include "Tuber, beet, etc" , "Eg, potatoes" , "Potatoes or carrots" , "Maybe Murphy" , "Swedes, say" .)

I've seen this clue in The Telegraph.

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