I am looking at covering my newly hung drywall with a local clay plaster: 1 part clay: 3 parts sand : 1 part fibre.
I have done experiments on some practice pieces to ensure it will adhere OK. Some with a flour/ sand and/or clay precoat to see which one adheres the plaster to the drywall best.
So I am wondering if it is necessary to tape my drywall joints since the plaster will be put on almost a half inch thick when finished the 3 coats or will cracks eventually show up at the joints if I don't tape them?
You definately needed to tape the joints. I would almost go as far as telling you that you probably should use stucco mesh wire as well. Your plaster may or may not adhere properly, especially over time, when it is just smeared on basically a smooth surface such as drywall.