<h3>What does 'nitrogen' mean?</h3>

<p>Nitrogen might mean gaseous $N_2$. It might also mean compounds, which contain nitrogen, such as nitrate, ammonia and ammonium.</p>

<h3>$N_2$</h3>

<p>$N_2$ cannot be metabolized by most plants because it is to inert. You need bacteria or plants (e.g. Legume family plants) to perform nitrogen fixation. During this processes the $N_2$ is converted into bio-available compounds such as ammonia. If these plants/bacteria are not present, the $N_2$ is useless and does not increase the fertility.</p>

<h3>Nitrate and Ammonium/Ammonium</h3>

<p>Ammonium and nitrate can directly be 'used' by plants and soil bacteria. Therefore, if we provide these compounds, we increase the fertility.</p>

<h3>Summary</h3>

<p>Generally, 'nitrogen' does not increase the fertility of soils but depends on how it is bound - elemental or in a bio-available form. Therefore, 'nitrogen' does not necessarily increase the fertility. In contrast, nitrogen fixing bacteria do increase the fertility of the soil (also long as $N_2$ concentrations in the atmosphere are as high as present).</p>

CC BY-SA 3.0
2017-06-13T13:59:51.420Z
2017-06-13T13:59:51.420Z
daniel.heydebreck
<p>The answer is Nitrogen. Pay attention that nitrogen must be mineralized before it is available for plants:
<a href="https://cropaia.com/blog/nitrogen-in-plants/" rel="nofollow noreferrer">https://cropaia.com/blog/nitrogen-in-plants/</a></p>

CC BY-SA 4.0
2019-08-26T07:40:30.663Z
Welcome to the site, but please do not repeat answers
Jan Doggen
CC BY-SA 4.0
2019-08-25T12:53:40.350Z
2019-08-25T12:53:40.350Z
Guy
<p>From this paper from 1958 (page 2), </p>

<blockquote>
  <p>... <strong>gaseous nitrogen</strong> of the atmosphere represents a vast store of potential
  fertility. It <strong>is not directly available to plants</strong>. Nitrogen-fixing bacteria, how-
  ever, absorb this gas from the soil solution and convert it to cell protein.
  When the cells die, other microbes attack the protein and convert the nitro-
  genous constituents to ammonium, which then becomes an available nutrient.
  Similarly, microbial action on plant and animal residues releases the many
  combined nutrients from their unavailable forms.</p>
</blockquote>

<p>From this, one of the criteria for soil to be fertile is the availability of nitrogen to be available to plants in a readily usable form. In a two stage process, one group of microbes (bacteria) fixes the nitrogen by converting into a protein, within their cells. When this group of microbes die, another group of microbes uses these proteins to produce ammonia, which is a nutrient that plants can use. </p>

<p>Also, as <a href="http://www.astrobio.net/also-in-news/bacteria-needed-to-make-fertile-soil/" rel="nofollow noreferrer">this article states</a>, dead bacteria are critical to soil fertility, because nearly 40 percent of a the biomass of bacteria are converted to organic soil components.
strong text</p>

<p><strong><a href="https://en.wikipedia.org/wiki/Nitrogen_cycle" rel="nofollow noreferrer">The Nitrogen Cycle</a></strong></p>

<p><a href="https://i.sstatic.net/1mVrZ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1mVrZ.png" alt="enter image description here"></a></p>

CC BY-SA 3.0
2017-06-13T18:08:56.377Z
Then you say that the correct answer to my MCQ is nitrogen?! You agree with me then. But what about the book answer?
Asmaa
CC BY-SA 3.0
2017-06-14T01:23:19.460Z
@Asmaa: No. Plants cannot absorb nitrogen directly from the atmosphere, they need bacteria to make nitrogen in a form they can use.
Fred
CC BY-SA 3.0
2017-06-14T07:05:30.757Z
Oh, OK, I got it.
Asmaa
CC BY-SA 3.0
2017-09-30T17:40:10.480Z
@Fred The link on the nitrogen cycle seems to be broken. Is [this](http://wtamu.edu/~cbaird/sq/2014/02/21/how-do-plants-get-their-nitrogen-from-the-air/) what you were referring to?
Luc M
CC BY-SA 3.0
2017-06-13T14:07:48.017Z
2017-10-01T01:04:11.620Z
2017-10-01T01:04:11.620Z
Fred
<p>I came across this question in my book, it says:</p>

<blockquote>
  <p>The fertility of the soil increases when there is a lot of ....... in it.</p>
</blockquote>

<p>The choices to fill the space were:</p>

<blockquote>
  <p>Nitrogen - nodular bacteria - fungi</p>
</blockquote>

<p>I would exclude fungi as in my course I don't have anything says that fungi affect the fertility of the soil. Both nitrogen and nodular bacteria are good choices and I am confused between them. Nitrogen is an important nutrient, nodular bacteria are the nitrogent-fixing bacteria, so both are important to the firtility of the soil, but I chose nitrogen, as I thought it is more correct, but I found that the answer was "nodular bacteria" so why is this? Is there anything I don't understand?</p>

<homework><soil>
The fertility of the soil
Asmaa
# The fertility of the soil

(Asked by: username_0 on 2017-06-13)

I came across this question in my book, it says:

> The fertility of the soil increases when there is a lot of ....... in it.

The choices to fill the space were:

> Nitrogen - nodular bacteria - fungi

I would exclude fungi as in my course I don't have anything says that fungi affect the fertility of the soil. Both nitrogen and nodular bacteria are good choices and I am confused between them. Nitrogen is an important nutrient, nodular bacteria are the nitrogent-fixing bacteria, so both are important to the firtility of the soil, but I chose nitrogen, as I thought it is more correct, but I found that the answer was "nodular bacteria" so why is this? Is there anything I don't understand?

**Tags:** homework, soil


---

## 3 answers

### Answer by username_4 on 2017-06-13. Score: 8 | Accepted answer

From this paper from 1958 (page 2),

> ... **gaseous nitrogen** of the atmosphere represents a vast store of potential
> fertility. It **is not directly available to plants**. Nitrogen-fixing bacteria, how-
> ever, absorb this gas from the soil solution and convert it to cell protein.
> When the cells die, other microbes attack the protein and convert the nitro-
> genous constituents to ammonium, which then becomes an available nutrient.
> Similarly, microbial action on plant and animal residues releases the many
> combined nutrients from their unavailable forms.

From this, one of the criteria for soil to be fertile is the availability of nitrogen to be available to plants in a readily usable form. In a two stage process, one group of microbes (bacteria) fixes the nitrogen by converting into a protein, within their cells. When this group of microbes die, another group of microbes uses these proteins to produce ammonia, which is a nutrient that plants can use.

Also, as [this article states](http://www.astrobio.net/also-in-news/bacteria-needed-to-make-fertile-soil/), dead bacteria are critical to soil fertility, because nearly 40 percent of a the biomass of bacteria are converted to organic soil components.
strong text

**[The Nitrogen Cycle](https://en.wikipedia.org/wiki/Nitrogen_cycle)**

[![enter image description here](https://i.sstatic.net/1mVrZ.png)](https://i.sstatic.net/1mVrZ.png)

> **Comments:**
> **username_0**: Then you say that the correct answer to my MCQ is nitrogen?! You agree with me then. But what about the book answer?  
> **username_4**: @username_0: No. Plants cannot absorb nitrogen directly from the atmosphere, they need bacteria to make nitrogen in a form they can use.  
> **username_0**: Oh, OK, I got it.  
> **username_5**: @username_4 The link on the nitrogen cycle seems to be broken. Is [this](http://wtamu.edu/~cbaird/sq/2014/02/21/how-do-plants-get-their-nitrogen-from-the-air/) what you were referring to?  

---

### Answer by username_1 on 2017-06-13. Score: 5

### What does 'nitrogen' mean?

Nitrogen might mean gaseous $N\_2$. It might also mean compounds, which contain nitrogen, such as nitrate, ammonia and ammonium.

### $N\_2$

$N\_2$ cannot be metabolized by most plants because it is to inert. You need bacteria or plants (e.g. Legume family plants) to perform nitrogen fixation. During this processes the $N\_2$ is converted into bio-available compounds such as ammonia. If these plants/bacteria are not present, the $N\_2$ is useless and does not increase the fertility.

### Nitrate and Ammonium/Ammonium

Ammonium and nitrate can directly be 'used' by plants and soil bacteria. Therefore, if we provide these compounds, we increase the fertility.

### Summary

Generally, 'nitrogen' does not increase the fertility of soils but depends on how it is bound - elemental or in a bio-available form. Therefore, 'nitrogen' does not necessarily increase the fertility. In contrast, nitrogen fixing bacteria do increase the fertility of the soil (also long as $N\_2$ concentrations in the atmosphere are as high as present).


---

### Answer by username_2 on 2019-08-25. Score: 0

The answer is Nitrogen. Pay attention that nitrogen must be mineralized before it is available for plants:
<https://cropaia.com/blog/nitrogen-in-plants/>

> **Comments:**
> **username_3**: Welcome to the site, but please do not repeat answers  

---

