Solr supports the creation of multiple Solr cores, each of which contains a unique Solr index. Each core can be
defined to use different configuration files, including schema.xml. When an aggregated search across multiple cores occurs, each of the Solr cores searches its own data using its own configuration before returning results to be combined by another core. Because of this, it’s possible to have many language-specific cores with their own definitions for a particular field, which means that all documents and queries in that field will be handled differently on a per-Solr-core basis.
http://stackoverflow.com/questions/19313910/query-multiple-collections-with-different-fields-in-solr