According to Manga Time Kirara, two serializations of manga K-ON!
will start in Manga Time Kirara and Kirara Carat. The university part of Yui, Mio, Ritsu and Mugi will be serialized in Kirara magazine from April 9th. Kirara Carat will carry the high school part featuring Azusa, Ui and Jun from April 28th.
Source: Scan of Kirara