Legume on base adapted over year (7)
I believe the answer is:
soybean
'legume' is the definition.
(soybean is a kind of legume)
'on base adapted over year' is the wordplay.
'adapted' indicates an anagram.
'over' indicates putting letters inside.
'year' becomes 'y'.
'on'+'base'='onbase'
'onbase' with letters rearranged gives 'sobean'.
'sobean' placed around 'y' is 'SOYBEAN'.
(Other definitions for soybean that I've seen before include "American vegetable" , "Vegetable source of protein" .)