default entity reference from url.php

<?php

// node/add/project-review/%nid
$nid = arg(3); //Gets the nid from the url
if ($nid) {
  //get the project node
  $node = node_load($nid);

  //add the entity reference to the project of it does not already have one
  if (empty($form['field_project_refence'][LANGUAGE_NONE][0]['target_id']['#default_value'])) {
    $form['field_project_refence'][LANGUAGE_NONE][0]['target_id']['#default_value'] = $node->title . ' (' . $node->nid . ')';
  }

}