its was originaly naboo, but when Yoda farted, the extreme midichlorian count that was released into the air mutated all the surrounding area. This happens all the time with jedi, although they can usualy control it, sometimes under deep presure they just let fly. He also farted in a cave. You can tell because of the original liines for ep 5
Luke: Theres something... foul in there
Yoda: Safety