State partial elevation of this can aid nitrification (7)
I believe the answer is:
indiana
'state' is the definition.
(US state)
'partial elevation of this can aid nitrification' is the wordplay.
'elevation of' is a reversal indicator (letters written upwards in a down clue).
'partial' says the answer is hidden in the clue.
'anaidni' can be found hidden inside 'this can aid nitrification'.
'anaidni' back-to-front is 'INDIANA'.
(Other definitions for indiana that I've seen before include "___ Jones, Harrison Ford hero - US state" , "state of America" , "part of USA" , "--- Jones, Harrison Ford film character" , "___ Jones (Raiders of the Lost Ark)" .)