Nitrogen,total

Nitrogen, total(organic and inorganic) is not a single chemical substance but a wide range of compounds of nitrogen which can be used directly by plants as a source of nitrogen required for their nutrition directly, or else may be converted into forms that plants can use in the environment.Nitrogen gas makes up about 80% of the atmosphere and is fairly non-reactive. Before living organisms can make use of nitrogen as a nutrient element, it has to be in a soluble form, such as nitrate or ammonia (inorganic forms) or in organic forms such as proteins which are readily converted into inorganic forms. The key inorganic form of nitrogen is ammonia, a highly reactive gas in its pure form, but which is usually found as ammonium ions when dissolved in water. Ammonium ions are the form of nitrogen used by plants and animals to make amino acids which are then built up into the structural proteins and enzymes that are the key components of all living organisms. The other main inorganic form of nitrogen is the nitrate ion (derived from nitric acid). Nitrate and ammonia are inter-converted in the water and soil by micro-organisms. These inorganic forms are taken up by plants and converted to proteins. Higher animals could not use inorganic forms of nitrogen for their nutrition but instead depend on organic forms already made by the plants and other animals that they eat. Proteins in the animal diet are first broken down into their constituent amino acids and are then reassembled into the required animal proteins and other cell constituents. Waste organic nitrogen compounds in animals are converted into ammonia, and then excreted in the urine as urea and other simple organic forms. These substances then enter the environment where they are converted into nitrate, ammonium ions and nitrogen gas. Some specialised bacteria can also 'fix' nitrogen gas from the atmosphere into ammonium ions. The above process is called the nitrogen cycle. In addition to ammonium and nitrate ions, traces of unstable inorganic nitrogen compounds such as nitrite ions may occasionally be found.