Region of bare arable land (4)
I believe the answer is:
area
'region' is the definition.
('area' can be a synonym of 'region')
'of bare arable land' is the wordplay.
'of' indicates the answer is hidden within the clue.
'AREA' is hidden within 'bare arable land'.
(Other definitions for area that I've seen before include "Field of activity or surface" , "Speaking formally to (someone)" , "Locality" , "Geographical region" , "Extent of a 2-dimensional surface" .)