In general Enterprise Architecture is about seeing the whole picture of a company - it is in some ways an abstraction to understand how an organization works. SOA's challenge is more to provide relevant services.

In fact a well designed EA might be a prerequisite of a successful SOA - otherwise development of services can become quite random. So SOA has to fit somehow within the overall Enterprise Architecture.

EA has the role of an organizational element plenty aspects like reference modeling or governance are not covered by SOA scope. Instead SOA relates to the way technology is actually deployed.

In that way SOA can be seen as a more practical approach but that does not mean it can replace an Enterprise Architecture. The effort should be to make the EA and SOA of an organization interoperate and complement each other.