Our group pursuing smell to find decomposing matter (5)
I believe the answer is:
humus
'decomposing matter' is the definition.
(I've seen this before)
'our group pursuing smell' is the wordplay.
'our group' becomes 'us'.
'pursuing' means one lot of letters go next to another.
'smell' becomes 'hum' (something with a bad smell is 'humming').
'us' put after 'hum' is 'HUMUS'.
'to find' acts as a link.
(Other definitions for humus that I've seen before include "Partially decomposed matter in the soil" , "decomposing organic matter" , "Soil's organic component" , "Organic stuff" , "Decomposed vegetation" .)