You should be able to compost salt peter with chickens, that's historically how we acquired it before we found deposits of it in the ground. Because chickens have urea in their manure so you only need to add wood ash to get potassium nitrate.
Also water wheels sound awesome, but they shouldnt be implemented until the devs are ready to tackle industrial age contraptions (please for the love of god let us make airplanes in the future, please. I am SOOOOO sick of running and jumping my freaking W key is getting loose.)
Also I feel like it would cool to add glass blowing into the game to make chemistry ware. But it would be a very extensive and exhausting endeavor to add even a little bit of actual chemical processes to the game so I get it if it sounds ludicrous.