Hey, just speculating (like Mayor Bloomberg), but it would be kind of interesting if the fertilizer used by this Faisal Shahzad schmuck turned out to have been non-explosive because it was Miracle-Gro liquid lawn feeder or something.
Stacy McCain has a couple of excellent roundups of reporting on the failed attempt to bomb Times Square, including this sweet Tweet from Andy Levy to Bloomberg.
Update - From Swampie in the comments: "If I were to detonate a fertilizer bomb made from products readily available at my place, there'd be a sheep shit cloud visible for miles. And the one made from duck droppings? You don't even wanna know."