mushrooms

I am going to be growing portobello mushrooms and they need a composted manure substrate and on of the main thing is the ammonia needs to be converted into a nitrate. Is there a way to do this cheaply?

My husband's old boss used to rave about the stuff, we always gave it to him when we found it. DH just found a bunch and we want to figure out what to do to make tea. He's read all about the health benefits, etc. (I if course won't be trying it while I'm pregnant because I'm neurotic and I doubt...