Answer: The man and the turkey cross the river, (the wolf and corn are safe together), he leaves the turkey on the other side and goes back across.
The man then takes the wolf across the river, and since he can't leave the wolf and turkey together, he brings the turkey back.
Again, since the turkey and corn can't be left together, he leaves the turkey and he takes the corn across and leaves it with the wolf.
He then returns to pick up the turkey and heads across the river one last time.
...... this is a very old riddle. lol I had forgotten about it.