Q: Is ammonium sulfate and 21-0-0 the same thing?
A: They are identical! It’s always good to remember in the back of your mind that fertilizers, whether organic or synthetic, are basically chemicals. Organic fertilizers are complex organic compounds; synthetic fertilizers, including 21-0-0, are sometimes simpler. Ammonium sulfate is a very simple chemical. The ammonium part provides nitrogen to plants when dissolved in water. The sulfur part provides sulfur and slightly acidifies the soil. If you have a bag of the chemical it will contain 21% nitrogen and nothing else but filler.