Cultivation augmented when catching up on fertiliser (5)

I believe the answer is:

guano

I'm a little stuck... Click here to teach me more about this clue!

'fertiliser' is the definition.
(I've seen this before)

'cultivation augmented when catching up' is the wordplay.
'GUANO' is hidden backwards within the letters.
But, I am unsure how this is indicated.

'on' is the link.

Can you help me to learn more?

(Other definitions for guano that I've seen before include "Manure from sea birds" , "Fertiliser (either from bird droppings or artificial)" , "One or more dropping by the coast" , "Natural fertiliser" , "MP's first address to House" .)

I've seen this clue in the Sydney Morning Herald.

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