Hi Vijay,
You can implement this using authorization object for the plant field. The authobject and its value (the plant number) can be included in the roles of the user who you would want to give access.
Below link will let you understand the concept and fulfill your requirement.
From the ABAP perspective, you need to include few lines of code to do the authorization check using the new auth object (or standard auth object).
AUTHORITY-CHECK OBJECT "your object"
ID WERKS FIELD 123
Regards,
Tashi