Give prior knowledge of mineral found in agricultural land (7)
I believe the answer is:
forearm
'give prior knowledge' is the definition.
'mineral found in agricultural land' is the wordplay.
'mineral' becomes 'ore' (ore is a kind of mineral).
'found in' means one lot of letters goes inside another.
'agricultural land' becomes 'farm' (I've seen this before).
'ore' put into 'farm' is 'FOREARM'.
'of' is the link.
(Other definitions for forearm that I've seen before include "where is the radius?" , "what's near to hand?" , "Prepare to defend" , "Before battle, take up weapon" , "part of body" .)