A new  ammonium sulfate nitrate (ASN) fertilizer  produced by a  fusion process has been patented by Honeywell. The product contains 62% ammonium sulfate (AS) and 38% of ammonium nitrate (AN) with a 2:1 (AN:AS) double salt and free AS. Compared to simple mixture of AS and AN, Sulf-N 26 fused ASN has two advantages: it is non-explosive and suitable for bulk-blending with urea. However, the effects of fusion process on possible agronomic benefits are unknown. This study was to compare ammonia (NH₃) volatilization from the granular fused ASN with granulated mixture (by dry compaction) of AS and AN on calcareous soils. The two products had about the same granular size and chemical composition. They were compared with urea and other N sources. As expected, the amounts of NH₃ volatilized from urea were the highest. The most striking observation of the study was that the fused ASN significantly volatilized less NH₃ than compacted ASN, indicating the fusion process could reduce NH₃ volatilization from AS and AN on the calcareous soils. Possible explanations for the effect will be discussed.