Vocal opponents of department engineering farm machinery (10)

I believe the answer is:

detractors

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'vocal opponents' is the definition.
The definition and answer can be both people as well as being plural nouns.
Perhaps there's a link between them I don't understand?

'department engineering farm machinery' is the wordplay.
'department' becomes 'd' (abbreviation eg in MOD Ministry of Defence).
'engineering' becomes 'e' (abbreviation).
'farm machinery' becomes 'tractors' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'd'+'e'+'tractors'='DETRACTORS'

'of' acts as a link.

Can you help me to learn more?

(Other definitions for detractors that I've seen before include "Disparagers" , "Critical persons" .)

I've seen this clue in The Irish Times.

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