Treat the soil to get fruit (4)
I believe the answer is:
lime
I believe this clue is a double definition.
'treat the soil' is the first definition.
(to lime soil is to treat it with lime)
'fruit' is the second definition.
(lime is a kind of fruit)
'to get' is the link.
(Other definitions for lime that I've seen before include "Acid green fruit like a lemon" , "Round green fruit or a linden tree" , "Type of stone" , "Another name for the linden tree" , "Kind of tree or substance used in cement" .)