A crop of nut (5)
I believe the answer is:
acorn
'nut' is the definition.
(I've seen this in another clue)
'a crop' is the wordplay.
'crop' becomes 'corn' (a farmer's crop of corn).
'a'+'corn'='ACORN'
'of' is the link.
(Other definitions for acorn that I've seen before include "Source of a great oak" , "Potentially future tree" , "cup's content" , "fruit in a cup" , "old computer?" .)