Fertilizers

Abstract

Fertilizers, classified according to grades reflecting quantities of the three primary plant nutrients, are usually nitrogen, phosphorus, or potassium based. The main function of chemical fertilizers is to supply one or more of these primary nutrients in chemical forms that can be assimilated through plant roots. One or more of the secondary nutrients, calcium, magnesium, or sulfur, or a variety of micronutrients may also be present. Mixed fertilizers are also available. Application is generally through the soil and must be in a chemical form assimilable by the particular crop. Gaseous, liquid, or solid materials may be used. Manufacturing processes for the various physical forms are described. The nitrogen in chemical fertilizers is derived almost entirely from synthetic ammonia. The phosphorus is derived from extensive mineral deposits, mostly by processes that involve beneficiation of the ore followed by solubilization in sulfuric acid. The potassium sources for fertilizers are salt deposits and brine lakes or wells. Anhydrous ammonia is the most economical nitrogen‐based fertilizer in the United States. Urea is also very popular.