Initially made awful noise upending really expensive fertilizer (6)

I believe the answer is:

manure

'fertilizer' is the definition.
(manure is a kind of fertilizer)

'initially made awful noise upending really expensive' is the wordplay.
'initially' suggests taking the first letters.
The initial letters of 'made awful noise upending really expensive' is 'MANURE'.

(Other definitions for manure that I've seen before include "Natural animal fertiliser" , "Organic fertiliser" , "Animal excreta used to fertilise land" , "Dung as fertiliser" , "Muck" .)

I've seen this clue in The Guardian.

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