부산대학교 도서관

The process of turning free nitrogen gas (N2) into chemical compounds, usually ammonia (NH3), which can be used by growing plants as a source of nitrogen. Gaseous N2 makes up the majority of the atmosphere, but higher organisms cannot use it because the N2 molecule is extremely stable and unreactive. Nitrogen-fixing reactions are vital for life on Earth because all organisms contain nitrogen atoms in essential molecules such as DNA, RNA, and proteins. Natural nitrogen fixation is done by microorganisms through the action of the nitrogenase enzymes. Chemical N2 fixation is done through the Haber-Bosch process, which is used to produce more than 200 million metric tons (220 tons) of ammonia per year. World agricultural production is highly dependent on nitrogen fixation. It is because of the need for fertilizers that chemical nitrogen fixation is done on such a gigantic scale. The amount of ammonia manufactured by the chemical industry is greater than the amount of natural nitrogen fixation, and the world's population could not be supported without this input of fixed nitrogen. However, the additional fixed nitrogen in the environment has led to pollution by nitrate (NO-3) and nitrite (NO-2) in natural waters.