Study after turf becomes waterlogged (6)
I believe the answer is:
sodden
'waterlogged' is the definition.
(I've seen this before)
'study after turf' is the wordplay.
'study' becomes 'den' (term for a study or office).
'after' is a charade indicator (letters next to each other).
'turf' becomes 'sod' (both can mean a piece of grass).
'den' put after 'sod' is 'SODDEN'.
'becomes' acts as a link.
(Other definitions for sodden that I've seen before include "heavy with moisture" , "Drenched through, really wet" , "Made very wet" , "Completely saturated" , "Thoroughly wet, soaked" .)