Fertilizer hidden backward in "come to naught" (5)

I believe the answer is:

guano

(Other definitions for guano that I've seen before include "Fertiliser from sea birds" , "Manure from seabird or bat" , "type of fertiliser" , "Fertilizer from the waste of seabirds" , "Excrement of sea birds, used as fertilizer" .)

I've seen this clue in the Universal.

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