In autumn it requires gunpowder ingredient (5)
I believe the answer is:
nitre
'gunpowder ingredient' is the definition.
(I've seen this before)
'in autumn it requires' is the wordplay.
'in' says the answer is hidden in the clue.
'NITRE' is hidden within 'autumn it requires'.
(Other definitions for nitre that I've seen before include "what goes into bangers" , "Also known as salt-petre" , "explosive component" , "safeguard against decay" , "Salt" .)