For desktop browsers I can set this on a field to disable the auto-completion list based on recent entries.
<input type="text" name="username" autocomplete="off"/>
^^^^^^^^^^^^^^^^^^
However this doesn't disable the auto-suggestion feature of iPad / iPhone / Android / etc. which can be very frustrating if your username is a concatination of your first/last name or if your device thinks you want to upper case the first letter.
e.g. "jsmith" either becomes "Smith" because it thinks you miss-spelled it or "Jsmith" to try and be nice... neither of which is really desired.
Thus the question is... is there a way to disable this behavior on a per field basis?
You are wanting to use the attribute autocorrect instead of autocomplete. The attribute autocomplete is used for form autofill.