Hard core of soil removed in open country (5)
I believe the answer is:
heath
'open country' is the definition.
(I've seen this before)
'hard core of soil' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'core of' says to hollow out the word (remove centre letters) (I've seen 'cored' mean this).
'soil' becomes 'earth' (synonyms).
'earth' with its middle removed is 'eath'.
'h'+'eath'='HEATH'
'removed in' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for heath that I've seen before include "Scrubland" , "Common land; ex-PM" , "Sir Edward - , PM" , "Open land with acid soil" , "Statesman" .)