In a medium-sized bowl, mix salt, brown sugar, rosemary, and garlic powder until fully incorporated. Place turkey on a roasting rack inside a large roasting pan. Pat mixture all over the entire surface area of the turkey, inside and out. Chill in the refrigerator uncovered (air needs to surround the turkey) for 48 hours.
About 1 hour before you will be cooking the turkey, remove turkey from refrigerator and rinse thoroughly. Pat turkey until completely dry. Allow to come to room temperature before you cook the bird. It will cook more evenly and more quickly.
Your turkey has been brined and is now ready to fry, roast, or smoke!