Part of body buried in rich earth (5)
I believe the answer is:
heart
'part of body' is the definition.
('heart' is part of 'body')
'buried in rich earth' is the wordplay.
'buried in' indicates a hidden word.
'HEART' is hidden in the letters of 'rich earth'.
(Other definitions for heart that I've seen before include "show enthusiasm" , "Middle" , "Vital organ - centre - courage" , "the name of a prison in Midlothian!" , "Earth (anag) -- compassion" .)