Study on turf heavy with moisture (6)
I believe the answer is:
sodden
'heavy with moisture' is the definition.
(I've seen this before)
'study on turf' is the wordplay.
'study' becomes 'den' (den can mean an office or study).
'on' says to put letters next to each other.
'turf' becomes 'sod' (both can mean a piece of grass).
'den' after 'sod' is 'SODDEN'.
(Other definitions for sodden that I've seen before include "Soaked to the skin" , "Waterlogged" , "Muddy" , "Completely saturated" , "Drenched, really soaked" .)