In Iraq, insurgent networks had a motherlode of military-grade explosives for making roadside bombs. In Afghanistan, fertilizer bombs are the weapon of choice, making detection and interception a much greater challenge, according to the head of the Pentagon's bomb-fighting organization.

In a bloggers roundtable today, Lt. Gen. Michael Oates, Director of the Joint IED Defeat Organization, said that Gen. Stanley McChrystal, the top U.S. commander in Afghanistan, had lobbied Afghan President Hamid Karzai to impose a ban on ammonium nitrate fertilizer, one of the common ingredients for homemade explosives.

"When Gen. McChrystal identified the threat to troops from ammonium nitrate-based fertilizers – none of which are produced in Afghanistan – he went to President Karzai and in very quick order, he had a presidential ban issued on ammonium nitrate fertilizers, both in the country and for importation," Oates said.

Oates added, however, that it was also difficult to detect ammonium nitrate if it was smuggled across the border from Pakistan. "There's been a concerted effort to working with the Pakistani government to shut down the transshipment of of precursors," he said.

The picture above shows a pile of ammonium nitrate discovered in a cordon and search of the Shawal bazaar in Kandahar. But as Afghan and coalition security forces capture stashes more ammonium nitrate, insurgents may turn other ingredients, such as potassium chlorate.

While there is not a ban on these materials in Pakistan, Oates said there were "serious discussions involving the Pakistanis" about restricting the sale of both ammonium nitrate and potassium chlorate.

For fighting these primitive bombs presents another challenge: They do not have a high metal content that can be easily detected. Oates said "persistent surveillance" on Afghanistan's road network would be key, although that's easier said than done. "Getting these persistent surveillance capabilities into Afghanistan is a transportation challenge," he said.

[PHOTO: U.S. Department of Defense]