Crop circles as chopped down seed (6,3)
I believe the answer is:
cashew nut
'seed' is the definition.
(cashew nut is a kind of seed)
'crop circles as chopped down' is the wordplay.
'crop' becomes 'cut'.
'circles' means one lot of letters goes inside another.
'chopped down' becomes 'hewn' (I've seen this before).
'as'+'hewn'='ashewn'
'cut' enclosing 'ashewn' is 'CASHEW NUT'.
(Other definitions for cashew nut that I've seen before include "Product of tree" , "Edible fruit of American tree" , "Kidney-shaped snack" , "Rich source of oil and protein" .)