[silverleaf]

So how big a “boom” would that make?

[Eric in the Ozarks]

Big boom. When I was in the coal biz, we used about 300 pounds per hole on a bench that had 40 to 50 holes to blast the overburden. This would fracture a chunk of shale 90 feet tall by 100 feet wide and 80 feet long.

[river rat]

"So how big a “boom” would that make?"

More than enough to require "special elections" in most of the States.

[Anitius Severinus Boethius]

Tim McVeigh used about 3.5 tons of chemicals for his bomb. This would take down a good 10 story building.

[Aglooka]

So how big a “boom” would that make?

The bomb that McVeigh and Nichols made used had 6200 lbs of ammonium nitrate mixed with nitromethane (racing fuel) and diesel fuel. (Source: wikipedia).

It could be that someone really just stole this fertilizer to either sell or use.

[DBrow]

You can't make a bomb directly starting with urea. You need other chemicals in large quantity to make explosives with urea as the start.

Ammonium nitrate is a bit different. ANFO or ANIS is well known in the improvised explosives field.

Neither an AN bomb or urea-based device will go off without a booster, it's not “cap sensitive”.

The most likely reason for the theft is fertilizing fields.