Limits borders of cash crops (4)

I believe the answer is:

caps

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'limits' is the definition.
(capping is a kind of limiting)

I don't understand the remainder of the clue.

(Other definitions for caps that I've seen before include "Head-coverings" , "Crowns" , "Style of GBS writing" , "Coverings for heads or bottles" , "is better" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

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