org-reverse-note-order

org-reverse-note-order is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means store new notes at the beginning of a file or entry.
When nil, new notes will be filed to the end of a file or entry.
This can also be a list with cons cells of regular expressions that
are matched against file names, and values.

You can customize this variable.