rinoldi,
The requirements for flying at a field are determined by who owns the field. If the field is privately owned then you will have to follow their guidelines. If they say club membership and an AMA card are required to fly then those are what you will need. If the field is publicly owned then whoever owns the field (i.e. city, state, US government) will outline the guidelines. If they are allowing a club to use a public field then they will usually defer to the club as to guidelines for use of the field.

For example. The field where I fly is located on an Army base. The requirements for flying there are that you have to an AMA card UNLESS you are active duty military, DOD civilian, or retired military. Since the army has set those guidelines we can't overrule them and have military members join the AMA. We encourage them to because of the insurance but we can't force them.

Hope this helps

Ken

Ken