Ammonium Nitrate requires a fuel source (ref: “The Fire Triangle”) to be come flammable/explosive.
The amount of fuel and container characteristics determine either flammable or explosive.
30 tons of Ammonium Nitrate is just A LOT of fertilizer.
And, with the current economic environment, has a good amount of value in the “No Tax and Regulation Market” (AKA Black Market)
And DS obviously has access to high explosives and really doesn't need to use low explosives for its false flags/terror events.