Improved border patrols by Afghan security forces, more U.S. troops, better tips from insurgents and intercepted communications have also resulted in more seizures, Morrison said. One seizure Sunday in Helmand province netted nearly 4,000 pounds of ammonium nitrate, the U.S. military said. The interdiction effort is worthwhile but exceptionally difficult, said Dakota Wood, a retired Marine officer and military analyst at the Center for Strategic and Budgetary Assessments. U.S. and Afghan officials have been encouraging farmers there to raise crops to bolster the economy and denying them fertilizers runs counter to that, he said. “You can’t ignore making an effort, but it will be hard to remove this from the bombmaking chain,” Wood said.