org-blank-before-new-entry

org-blank-before-new-entry is a variable defined in `org.el'.
Its value is

((heading . auto) (plain-list-item . auto))

Documentation:
Should `org-insert-heading' leave a blank line before new heading/item?
The value is an alist, with `heading' and `plain-list-item' as CAR,
and a boolean flag as CDR. The cdr may also be the symbol `auto', in
which case Org will look at the surrounding headings/items and try to
make an intelligent decision whether to insert a blank line or not.

For plain lists, if `org-list-empty-line-terminates-plain-lists' is set,
the setting here is ignored and no empty line is inserted to avoid breaking
the list structure.

You can customize this variable.