The Nitrogen Cycle

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Most of the Earth’s atmosphere is nitrogen (78%). When humans and all living things take a deep breath, most of what they just inhaled is nitrogen. All life needs nitrogen compounds, for examples are proteins and nucleic acids. For the plants, chlorophyll molecules use most of the nitrogen which are important for photosynthesis and further development. The quantity of nitrogen gas being permanently at any given time by natural processes produces only a small increase by fixed nitrogen that rotates among the living and non-living components of the Earth’s ecosystem (Peter et al., 1997). Nitrogen cycle is the process where nitrogen is switched between its various chemical forms. The vital processes of nitrogen cycle are nitrogen fixation, nitrification, ammonification, assimilation and denitrification (Steven & Steven, 2004).
The first stage involved in nitrogen cycle is nitrogen fixation. The nitrogen gas from the atmosphere cannot be used directly by the plants, so it is converted to ammonia first (refer to figure 1). The process of converting nitrogen gas to ammonia is carried out by the bacteria that lived in the roots of legumes such as peas, soybeans, and peanuts (White, 1979). This bacterium is known as Rhizobium (Zahran, 1999). It acts as the primary nitrogen fixer by infecting the roots of leguminous plants which result in the formation of nodules where the process of nitrogen fixation takes place. The enzyme nitrogenase is responsible in catalyzing the entire reaction occurs during nitrogen fixation by adding electrons and hydrogen ion (Haider & Schaffer, 1993).
The second stage in the nitrogen cycle is nitrification which can further divide into two phase. The first phase is the oxidation of ammonia to nitrite. The ...

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