Personally, I would look up field notes themselves or more specifically field note citations for ethnographic work. This yields countless anthropological works and the various ways they have been cited. That is what I have done in the past as not all citation styles eg Harvard, BPS, MLA etc have concrete and established systems for this. Best of luck.
I am also sharing this dilemma, with ref to interviews. I do not know whether it is okay to say in the footnote "During a structured interview with (name of the person) on (Topic) at (place) on (date). For full details see Annexure A". Give the complete bio of the person interviewed with the structured questionnaire and answer as an Annexure. In case there is an audio recording, annex the CD containing the interview.
Well, in case someone says this is fine, may be both of us could use such footnotes!
Often the need to anonymity in research ethics means that identifier information must be removed. This can preclude attaching the interview recordings and field diary notes. The standard way to cite field notes is to put the quote in quotation and the (fieldnotes, date) either after or in the footnote.