Cycles of Matter in Soil, Nitrogen Cycle

Nitrogen is another bioelement of crucial importance, being a part of amino acids, proteins, nucleic acids, and many other organic compounds. It is also an object to a complex natural cycle occurring, among others, at the soil level. Ammonification is one of the main components of this cycle, consisting of the decomposition of nitrogencontaining organic compounds and releasing ammonium ions, essential nutrients for plants and microorganisms. Another nitrogen input source in soils is the fixation of atmospheric dinitrogen by some bacteria, free-living or in symbiosis with certain plant species. Nitrification converts ammonium into nitrate, another valuable nutrient, soluble and easily disseminated in soil solution and hydrosphere. Microbial denitrification closes the cycle by transforming nitrate into nitrogen oxides and, then, dinitrogen that returns to the atmosphere. 

Keywords: Ammonification, Denitrification, Fixation, Nitrification, Nitrogen.