Fertiliser made of bird droppings (5)

I believe the answer is:

guano

(Other definitions for guano that I've seen before include "dried excrement" , "Fertiliser (either from bird droppings or artificial)" , "Manure from sea birds" , "mess about by the sea" , "Fertilizer from the waste of seabirds" .)

I've seen this clue in The Guardian.

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