The general situation of fertilizer application in USA

USA is the largest fertilizer producer and consumer in the world. Anhydrous ammonia, urea, diammonium phosphate and potassium chloride are among the most important fertilizers in United State in addition to mixed or compound fertilizers. The total amounts of fertilizer applied each year has been stabilized for the past decade, among which, over 90% are applied on the four staple crops. Soil testing is the common method for fertilizer recommendation. Fertilizer application is mainly completed by mechanized applicator. The potential impact of fertilizer use on the environment has been drawn great concern. Variable rate technology in fertilizer application needs to be extended to practical use.