Now wait just a minute. AFAIK urea is not useful as an explosive in it’s fertilizer state (usually Prills), the “other” fertilizer is what’s of concern, IF it’s Ammonium Nitrate. But as far as this article goes, it could be 3 tons of Zoo Doo “fertilizer”.
Honestly, I do not know what kind of Fertilizer does what, but here’s some info regarding Urea from wikipedia:
“The substance decomposes on heating above melting point, producing toxic gases, and reacts violently with strong oxidants, nitrites, inorganic chlorides, chlorites and perchlorates, causing fire and explosion hazard.”