Friable soil (4)
I believe the answer is:
loam
'friable soil' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for loam that I've seen before include "Rich soil, good for growing" , "Rich soil consisting of a mixture of sand, clay and decaying organic materials" , "Type of soil" , "A rich fertile soil" , "Rich soil with decayed vegetable matter" .)