A good candidate IMO for farming on Mars is the aquaponic model.  It's a mostly closed system, and produces meat as well as vegetables.  The biggest issue is keeping fish alive for the trip there.  The fish on the ISS didn't fare too well.,(reply>), I really need to make a video about aquaponics! The biggest advantage of using the martian soil versus aquaponics is the massive reduction in equipment you have to bring with you, from what I read during the making of this video!