Field study is depressing (6)
I believe the answer is:
leaden
'is depressing' is the definition.
(leaden can mean dull or depressing)
'field study' is the wordplay.
'field' becomes 'lea' (lea can mean a meadow or field of grass).
'study' becomes 'den' (term for a study or office).
'lea'+'den'='LEADEN'
(Other definitions for leaden that I've seen before include "Leaned over in slow, heavy way" , "Heavy - overcast" , "Heavy and slow, as if weighted down with heavy metal" , "Gloomy - slow-moving" , "Depressing - heavy" .)