Keirador is right, the Mississippian Indian cultures were very advanced agriculturally. It is a common stereotype to think of American Indians as nomadic, warlike tribes, who hunted buffalo and scalped settlers as a pastime, but in many instances this was simply not the case. Some anthropologists beleive there is a connection between Mississippian culture and Aztec culture, i.e. some of the Aztec ideas about agriculture may have filtered north before the Europeans arrived.
Another idea for a civ trait might be "Monumental" or "Architectural", this would reflect civilizations like the Romans and Greeks, who excelled at building grand temples, Colisseums, etc., not sure how you would implement it though.
One thing that might work is when a Civ gets to a tech in the area it really excels at, they get it for free, this could apply to at most 1 or 2 techs in whatever era their time of greatness ocurred. Need a few more techs in the tree, though, to keep worldwide research at a proper pace.