Kind of field changed to a vital grain (13)

I believe the answer is:

gravitational

'kind of field' is the definition.

'changed to a vital grain' is the wordplay.
'changed' is an anagram indicator.
'to'+'a'+'vital'+'grain'='toavitalgrain'
'toavitalgrain' is an anagram of 'GRAVITATIONAL'.

(Another definition for gravitational that I've seen is " Relating to bodily attraction".)

I've seen this clue in The Telegraph.

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