Ammonium Nitrate — Frequently Asked Questions

Because the compound contains both an ammonium and a nitrate ion. The nitrate half is immediately available to plants and moves freely in soil water; the ammonium half is held on soil colloids and is released more gradually as soil bacteria nitrify it. A single application therefore gives both a rapid response and a degree of persistence, at 34 percent total nitrogen.

Two reasons. It is strongly hygroscopic, so it absorbs atmospheric moisture and the dissolved surface recrystallises into bridges between prills. And it passes through a crystal phase change near 32 degrees Celsius, so material that is thermally cycled across that point repeatedly breaks down in prill structure and turns to powder. Coating and controlled storage address both.

Dry, in a dedicated area, away from heat sources, fuels, organic matter, combustible packaging and incompatible chemicals. It is a strong oxidiser: it does not burn itself but supplies oxygen that greatly intensifies any fire. Storage quantities, security and record-keeping are regulated in most jurisdictions and those requirements must be met.

It is controlled as an explosives precursor in the EU, UK, US and many other markets, so supply is subject to end-use verification, licensing and traceability requirements that vary by jurisdiction. The intended use and the purchaser's registration or licence status must be established before supply, and records are retained as the regulations require.