Saturated soil study (6)
I believe the answer is:
sodden
'saturated' is the definition.
('sodden' can be a synonym of 'saturated')
'soil study' is the wordplay.
'soil' becomes 'sod' (sod is a kind of soil).
'study' becomes 'den' (I've seen this before).
'sod'+'den'='SODDEN'
(Other definitions for sodden that I've seen before include "Drenched through, really wet" , "'Soaked, sopping (6)'" , "Thoroughly wet, soaked" , "Muddy" , "Totally saturated" .)