Productive bar is back in beer (6)
I believe the answer is:
arable
'productive' is the definition.
(similar in meaning)
'bar is back in beer' is the wordplay.
'is back' is a reversal indicator.
'in' is an insertion indicator.
'beer' becomes 'ale' (type of beer).
'bar' reversed gives 'rab'.
'rab' put within 'ale' is 'ARABLE'.
(Other definitions for arable that I've seen before include "Capable of being tilled" , "Of land, capable of growing crops" , "Of land, fit to be cultivated" , "Suitable for ploughing" , "Type of farming" .)