Nitrogen, is a major element and is found in both inorganic and organic forms within the plant. N is contained within amino acids, enzymes nucleic acids, chlorophyll, alkaloids and purine bases. N predominates as high molecular weight proteins. Absorbed as either the nitrate or ammonium ion. Nitrite is toxic to plants at levels less than 5ppm. It is the only nutrient with truly direct correlation between additions and growth.