I don't get this. Ammonium Nitrate fertilizer is an oxidizer. By itself, it should not be explosive. It requires a combustible material to be combined with it. Every explosion requires oxygen and a fuel. Oxygen on its own is not combustible. But add fine aluminum powder to that oxidizer -- now you have big boom if it's ignited.

I made little rocket engines from potassium Nitrate and powdered sugar. Such fun!