Anhydrous ammonia (AA) is the predominant fertilizer N source in Michigan in terms of the amount of actual N applied each year.There are several reasons why AA is used sowidely. First, because AA is the initial step in the manufacture of almost all commercial N, and second it is the least costly source of fertilizer N.Anhydrous ammonia also contains82% N, the highest nutrient concentration of any fertilizer. Anhydrous ammonia also has some drawbacks that limit its total domination of the fertilizer market.Because AA is a gas that is stored as a pressurized liquid, special application equipment is always required.This application is sometimes relatively slow compared to other products.As AA is released from tanks, it is a gas that can be a risk to human health ifproper safety precautions are not followed.As AA is discussed in respect to other fertilizer N products, often times information is stated that may or may not have a solid foundation.This article is a compilation of scientific data that has been evaluated from several perspectives of AA after it is applied to soil.