Anhydrous ammonia, the most commonly used nitrogen (N) fertilizer in Iowa, is unique in the ways it behaves in soils. Injected as a liquidgas mixture, it immediately reacts with the soil to form ammonium (NH4 + ), an ion that is strongly attracted to soil particles. Because of this strong attraction, the ammonium ions are retained in high concentrations that are localized within bands formed by the fertilizer applicator. The high ammonium concentration found in these bands is the major factor that distinguishes anhydrous ammonia from other fertilizers.