Due to Alfalfa not being a Base Game Crop the TMR Mixers do not accept Alfalfa Dry Hay Bales without doing some fancy xml work that I am not smart enough to do. What you could do is wrap your Bales and turn them into Baleage which the Mixers will accept after said Bales are done fermenting.
Viewing post in Courtland, MN 4X VERSION 1.1 (PLUS RCS EDITION) comments
If you go on Patreon and look for MRG Mapping you can join for Free and then become a Tester where you can get Discord Access and Map and Mod Access. On the Discord he has a Section for Bug Reporting where you can report things like your Hay/Alfalfa Bug. Both Patreon and Discord have a lot more features than itch does so that is why we prefer using it.