Create node and node reference from URL at one time
Depending on which relationship module you're using there are different options.


If you're using Entity Reference there's the Inline Entity Form module: 


  Provides a widget for inline management (creation, modification, removal) of referenced entities.
  The primary use case is the parent -> children one (product display -> products, order -> line items, etc.), where the child entities are never managed outside the parent form.

If you're using the References module there's References Dialog:


  This module extends reference fields like the user and node reference fields by adding links to add, edit and search for references through a dialog. This allows for a workflow where the user can create all the references to a node at the same time as she is creating it, a process which sometimes get's a bit backwards, when a user for instance needs to create all the facts for an article.



Both will allow you to create a referenced node at the same time as creating the referee.