Field yield (5)
'field yield' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for crop that I've seen before include "Harvest or kind of whip" , "Harvest yield" , "Reduce" , "Whip with loop instead of lash" , "supply" .)
(Other definitions for harvest that I've seen before include "Time to gather the crops" , "seasonal collection" , "Cut down" , "The fruits of tillage" , "Crop gathering" .)
(Other definitions for wheat that I've seen before include "Tall grass producing light brown grain" , "food plant" , "Grain crop" , "Hat we turn into grain" , "Source of flour" .)