Farm storage site (4)
'farm storage site' is the definition.
(I've seen this in another clue)
This is all the clue.
(Another definition for corncrib that I've seen is " agricultural store".)
(Other definitions for silo that I've seen before include "Grain storage tower" , "Grain container for oils" , "Farm grain storer" , "Storage unit for animal feed" , "Tower for making fodder" .)