Blend of crop is containing iodine as a sedative (9)
I believe the answer is:
soporific
'a sedative' is the definition.
(I've seen this before)
'blend of crop is containing iodine' is the wordplay.
'blend' indicates an anagram (I've seen this in other clues).
'containing' is an insertion indicator.
'iodine' becomes 'I' (I is the chemical symbol for iodine).
'of'+'crop'+'is'='ofcropis'
'ofcropis' is an anagram of 'soporfic'.
'soporfic' enclosing 'i' is 'SOPORIFIC'.
'as' acts as a link.
(Other definitions for soporific that I've seen before include "Sedative" , "Causing sleepiness" , "Inducing drowsiness or sleep" , "Inducing mental lethargy" , "making one nod" .)