How to reference a Current Node URL Prior/After a User submits a Rules Link trigger
A custom way to do it... Sorry not using Rules but it might help.

So you have two main node types ? And advert and an application ?
And the link to the application needs to contain the node ID of the advert.
I would use a custom link and hook_form_alter. For example;

If the apply link is only seen on the advert node page then you can use:

$nid = arg(1);
print l(t("Apply"), "node/add/application/$nid");


either in a node.tpl.php or in a preprocess function.

This will take the user to the node add form.
In a custom module you use hook_form_alter to get the $nid from the URL and add it to the form in the in the right field such as :

/**
 * Implements hook_form_alter().
 */
function custommod_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form['#id'] == 'application-node-form') {
    if (isset(arg(3))) {
      $form['field_advert_relation'][LANGUAGE_NONE][0]['target_id']['#default_value'] = arg(3);
    }
  }
}


This is for a normal entity reference field.
And the field could be disabled or hidden also.