I just bought a 50lb bag off amazonYeah, they are stinky! Ducks were my first farm-yard pet, so when I raised chickens for the first time I couldn't believe how CLEAN they were, lol! Now we have quail too, and I love having a brooder full of quail babies because you only have to change the bedding every few days or so. And the goats--I almost never change their bedding--it just doesn't get that dirty.
But the ducks--whew!!
The only thing is--I wish I knew where to buy baking soda in bulk. I use SO MUCH of it around the house that I want it in great big 50-lb bags, and if I'm going to use it in the barnyard too, I'm going to need more than a little kitchen box of it.
Actually, I don't know that I would try it outdoors--it would wash away so quickly, and I'm not sure how long-lasting it could possibly be. For a brooder it's perfect--it lasts long enough, since I have to change the bedding daily anyway. But outdoors--you'd probably have to sprinkle it daily. On the other hand, it might be worth it anyway. Let me hear how it works for you!