NARANJO DE CHILA, Mexico—Special squads of Mexican army troops equipped with metal detectors and bomb suits have deployed to the western state of Michoacan, where warring drug cartels have planted land mines or improvised explosive devices. The squads apparently have found dozens of such devices along rural roads and fields in the area around the township of Aguililla. The mines claimed their first civilian victim last week, when a farmer drove over one in his pickup truck; his son was wounded in the blast. That explosion was apparently fueled by a device containing ammonium nitrate. But the mines found so far have also included devices detonated by radio or telephone signal, by pressure—as when someone steps on them—or even by vials that break and combine two chemicals. On Friday, a soldier demonstrated how he cautiously approaches suspicious spots of disturbed soil on a dirt road in the area, before getting …