Post-mortem on harvests being constrained by rising Japanese currency (8)

'post-mortem' is the definition.
(I know that postmortem can be written as necropsy)

'harvests being constrained by rising japanese currency' is the wordplay.
'harvests' becomes 'crops' ('crop' can be a synonym of 'harvest').
'being constrained by' means one lot of letters goes inside another.
'rising' says the letters should be written in reverse (going up in a down clue).
'japanese currency' becomes 'yen' (I've seen this before).
'yen' reversed gives 'ney'.
'crops' going inside 'ney' is 'NECROPSY'.

'on' acts as a link.