Adding a field to a content type for Apache Solr search and Facets
Figured it out. Adding the answer in case anyone else needs it. Code below...

function issue_archive_apachesolr_index_document_build_node(ApacheSolrDocument $document, $node, $env_id) {
  if($node-&gt;type == "article") {
    $node = node_load($node-&gt;nid);
    $journal = node_load($node-&gt;field_journal['und'][0]['target_id']);
    $document-&gt;addField('its_field_year', $journal-&gt;field_year['und'][0]['value'] + 0);
    $document-&gt;addField('itm_field_year', $journal-&gt;field_year['und'][0]['value'] + 0);
  }
}

function issue_archive_apachesolr_query_prepare(DrupalSolrQueryInterface $query) {
  $query-&gt;addParam('qf', 'its_field_year');
  $query-&gt;addParam('qf', 'itm_field_year');
}


Using the solr_devel module, I saw that the journal type had two fields listed in the entity/document for year, one with the its_ prefix, and the other with the itm_prefix. I added both of those, and added the query field (I think that's what it stands for?) parameters to the query.

This got me the exact results I was looking for.