Actually releasing this turtle is not a wise idea at all.. if it was found in an area not suitable for permanent home, it may not be a wild turtle. And if it is, releasing it away from it's natural habitat will not help it.
Box turtles have built in homing instincts and a developed "home range" or area where they identify as "home" this may be as small an area as a football field or may be thousands of acres in size. However, if a turtle is displaced from his home, he will recognize it's not home and will spend the rest of his life searching to find the area he knows.
Releasing a box turtle away from it's natural habitat where it was found is probably not much better than letting him go where you found him.
To care for him- clean the wound with warm water... then let him soak 1-2 hours a day in water with betadine in it (get it at the local drugstore)... mix it to the color of tea. Then dress the wound with neosporin or similar ointment. he should heal up pretty well if you keep him warm and slightly humid. get him to eat worms, bananas (go easy on these) and fresh fruits.. maybe even some hamburger (again only a little)... he'll avoid commercial foods unless he's a pet.. so save your $$
And I'll offer to provide him a permanent home. I have a rescue for box turtles that can no longer live in the wild. They live and breed in a natural habitat living outside year round with minimal human interaction. Offspring are being saved for eventual release into the wild on a selected site that's monitored. The study is attempting to determine if captive bred offspring can successfully be intorduced into the wild.
If you'd like to discuss further care, and rehabilitation, I'll be glad to help.