Urea is one of the most concentrated fertilizers in nitrogen (46%) and normally the most economical on the market. It is marketed in pearled and granulated modalities, the first for use in fertigation and the second, for direct application to the soil. It is very soluble and often used in liquid formulations. Its high solubility makes it popular for injection into localized irrigation systems. It is classified as an ammoniacal source and therefore tends to acidify the soil.