KABUL (AP) - The Afghan government has banned a fertilizer chemical used in most of the homemade explosives that have killed and maimed hundreds of US and NATO soldiers here. NATO troops have seized tons of ammonium nitrate fertilizer in raids over the last five months in southern Afghanistan, and the government has been discouraging farmers from using it for years for environmental reasons.

Still, the government believes the new ban, announced Friday, will make it more difficult for the Taliban to replenish supplies of ammonium nitrate, which the US think tank Globalsecurity.com says has been used in more than 90 percent of the homemade bombs, the biggest killer of NATO troops in Afghanistan. Such ``fertilizer bombs’’ have also been used in Iraq in attacks against government security forces.

In the latest bombing fatality in Afghanistan, a British soldier was killed Friday by a blast in the southern province of Helmand. President Hamid Karzai issued the decree banning the use, production, storage, purchase or sale of ammonium nitrate.

Farmers have one month to turn in their stocks or face prosecution.

A number of countries, including Germany, Colombia, Ireland, the Philippines and China, have banned ammonium nitrate fertilizer and most US states regulate its use after the chemical was used in the 1995 Oklahoma City bombing, which killed 168 people, and the 2002 nightclub bombings in Bali in which 202 people died.

Mir Dad Panjshiri, an official in the Afghan Agriculture Ministry, said the government had been discouraging the use of ammonium nitrate fertilizer for years because urea fertilizer is better-suited to Afghan soils. He said businessmen began importing ammonium nitrate fertilizer in large amounts last year, mostly from Central Asia and Pakistan. ``We detected an increase in the use of the fertilizer over the past year by poor farmers in the southern provinces,’’ Panjshiri said. ``It’s not available everywhere. These poor farmers didn’t know what they bought.’’

He said the government was confident it could enforce the ban on its northern borders with Central Asia, but ``my concern is more in the south because we have a long border with Pakistan and it’s available there.’’