I would look into database normalization. In particular, your database is not even in 1st normal form, the first and probably most significant of the normal forms which states that normalized data should not contain any repeating groups. As a result, the Django object-relational-mapper will have considerable difficulty modeling your data.
By supporting only single, non-repeating types, Django in a sense enforces 1st normal form in data. You could try to write your own SQL to manage this particular field or perhaps find some code on the internet, but perhaps better would be to refactor this field into a many-to-one relationship in its own model. You can find Django documentation on this here.