org-footnote-define-inline

org-footnote-define-inline is a variable defined in `org-footnote.el'.
Its value is

nil

Documentation:
Non-nil means define footnotes inline, at reference location.
When nil, footnotes will be defined in a special section near
the end of the document. When t, the [fn:label:definition] notation
will be used to define the footnote at the reference position.

You can customize this variable.