It's eien no 'uta'. That character's 'default' reading is uta, so unless it is coupled with another character, for instance, 作詩 (sakushi; to write poetry) or if it is explicitly specified, it should be taken to be uta, which is really the norm if you look at many of the song titles with that character in them (DAI's 'shinjitsu no uta', le couple's 'hidamari no uta' etc etc).
|