# Nitrogen cycle semantics; nitrification/nitrogen fixation

Is 'nitrification' and 'nitrogen fixation' used interchangeably to describe biological reduction of $\ce{N2}$ gas to $\ce{NH3}$? I know $\ce{NH4} \to \ce{NO3}$ is called nitrification too.

• You might get a better answer in chemistry.stackexchange.com – arkaia Apr 25 '17 at 11:54
• do you want an answer of this for nitrogen cyckle in water or for soil,there is some differences.nitrification is the production of nitrate and nitrogen fixation is the storage of nitrate.there is also somthing called denitrification this is the release of nitrogen from nitrate. – trond hansen Apr 25 '17 at 13:15

I went to do a bit of research on this, and think that you can get a satisfactory answer just from the relevant wikipedia articles. Here are some select quotes:

Nitrogen fixation is a process by which nitrogen in the Earth's atmosphere is converted into ammonia (NH3) or other molecules available to living organisms.

Nitrogen fixation has the chemical process:

N$$_2$$ + 8 H$$^+$$ + 8 e$$^−$$ $$\rightarrow$$ 2 NH$$_3$$ + H$$_2$$

and is performed by Diazotroph bacteria or archaea. Some of these are symbiotic with plant roots, especially of the family Fabaceae.

Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate.

An example of a nitrification chemical reaction is:

2NH$$_4^+$$ + 3O$$_2$$ $$\rightarrow$$ 2NO$$_2^−$$ + 2 H$$_2$$O + 4 H$$^+$$

2NO$$_2^−$$ + O$$_2$$ $$\rightarrow$$ 2 NO$$_3^−$$

There are a wide variety of bacteria that peform these steps, and some only do one step or the other. There are also other pathways for reducing ammonia instead of ammonium, for example.

In conclusion, these are two different biologically driven steps in the nitrogen cycle, driven by two different sets of microorganims. There other biologically driven processes as well, such as ammonification, where organic nitrogen compounds in formerly living tissue (or waste) is broken down into ammonia or ammonium.

• I understand that N-fixation and nitrification are two separate processes in the N cycle. I was just wondering if at any time in the literature has the name ʻnitrificationʻ been used for the process of reducing atmospheric nitrogen gas to ammonia. The thing confusing me is in this article: link . In the first paragraph of section 6 they say that in the low oxygen Late Archaean Earth nitrification would be more important in imparting a del15N signature to fixed N... – chiaka Apr 25 '17 at 19:13
• But I understand that nitrification, being the oxidation of NH4 to NO3, requires sufficient oxygen in the environment. – chiaka Apr 25 '17 at 19:14
• @chiaka.dont forget to mark answers as accsepted when or if they are. – trond hansen Apr 26 '17 at 15:24