Nitrogen is really important in terms of human health. We all know how important nitrogen is.
There are so many other uses in terms of medicine, where reactive nitrogen helps us but also the threats particularly through air pollution and water pollution.
Nitrogen being really important in terms of biodiversity. Again, in terms of many species, their habitats are at risk from land use change, from climate change; and extra nitrogen enrichment can push them to extinction. So again, controlling nitrogen, using it more efficiently, can help.
To understand the effects of nitrogen pollution, firstly, we have to get familiar with the natural nitrogen cycle. Here you can see the upper and lower atmosphere, the soil and all our natural waters. Between the soil and the water there is a transition color. What happens here can equally happen in the soil or in the water.
Let’s see what happens with the ammonium in the soil! Firstly, it serves as a nutrient for plants. Secondly, some bacteria in the soil convert it to nitrate (NO3-). Loads of things can happen to nitrate. A part of it is taken up by plants as a nutrient.
A part of it, together with some of the ammonium, is leaching out from the soil to the natural waters. Here, both nitrate and ammonium serve as nutrients for aquatic plants and algae.
And finally, nitrate can go through another microbiological process, called denitrification, forming nitrogen gas and nitrous oxide (N2O). Nitrous oxide is a really stable compound, so it can get up to the upper atmosphere. Here, driven by the sun, in a so-called photochemical reaction, it is converted back to nitrogen gas.
This is however, a very slow process. It takes about 120 years for a nitrous oxide molecule to be converted to dinitrogen. Let’s go back to NOx originating from lightning! NOx is removed from the atmosphere through atmospheric deposition. This can be dry deposition, which happens when the tiny atmospheric vortexes transfer the molecules to the surface.
However, it can be also wet deposition, which happens when NOx is dissolved in atmospheric water droplets and washed out from the atmosphere with rain.
Both processes increase the nitrate content of the soil or the surface waters. There is a further aspect of the natural nitrogen cycle, which is the breakdown of animal excreta and dead organisms.
During the breakdown, especially from that of excreta ammonia (NH3) is formed while in the soil organic nitrogen is produced. This organic nitrogen is then transformed by soil microbes to ammonium. This process is called ammonification.
Finally, ammonia, similarly to NOx, is deposited to the surface, increasing the ammonium content of both the soil and the fresh waters. These processes are in balance in natural conditions but then come some human intervention. :( On one hand, from the atmospheric nitrogen gas we are synthesizing ammonia via the Haber-Bosch process to produce fertilizers. Fertilizers together with manure originating from livestock farming drastically increase ammonia emission as well as the ammonium content of the soil. Some fertilizers also increase the nitrate content of the soil.
The nitrate content of the soil will be also increased by the nitrification of the extra ammonium.
With more ammonium and nitrate in the soil more ammonium and nitrate will be washed out and more nitrous oxide will be emitted after denitrification.
But sadly we don’t stop here. We also disturb the natural nitrogen cycle through the emission of NOx. NOx is released during the combustion of fossil fuels where at high temperature, the nitrogen content of the air is oxidized to NOx. So this is the natural nitrogen cycle and the most important human activities influencing it.
Nitrogen is really crucial to agriculture, because all plant life on earth needs nitrogen to grow. Without it we wouldn’t have any of our crops, and as part of that we wouldn’t have grasslands, we wouldn’t have any animals, we wouldn’t have our food.
It’s been something, which has been a real challenge for humankind throughout civilisation, is actually, managing nitrogen, whether we knew it or not, actually, providing enough food for the people around the world, has always been reliant on having enough nitrogen in the right place at the right time.
We now globally rely on huge amount of nitrogen fertilisers to grow our food. If we go back into the dawn of agriculture, say, ten thousand years ago, we didn’t have these artificial fertilisers, and what we were doing when we were growing crops then, so the first farmers, was using the natural amounts of reactive nitrogen in the soil.
There’s small concentrations compared to the nitrogen gas that I’m breathing in now in large amounts, small concentrations of reactive nitrogen, and they occur in the soil, and when we plant a field with seed it will grow, and it will use some of that reactive nitrogen.
But what happened is, our human population expanded, and the agricultural use of our land increased, is that those stocks of reactive nitrogen in the soil began to be exhausted.
There’s a limit to how much naturally occurs. And with a growing population, obviously, then there’s a real risk of not having enough feed, of not being able to produce enough crops from a particular area of land.
And that real restriction went on right into the early 20th century, where we had a much bigger global population to feed, and the sources of this reactive nitrogen to grow crops were going really down.
So we have increasing bits of land where food was grown but over the years actually, the crop was getting less and less, because of less reactive nitrogen. And then we had the break through.
A man called Fritz Haber came up with a process to fix this nitrogen gas, that we’re all breathing in now. This inert form of nitrogen into a reactive form, that our crops could use.
And ever since he made that breakthrough, we’ve been increasingly using his process - the Haber process - to fix nitrogen and grow our crops, using artificial fertilisers.
So today the use is massive. Actually there’s more reactive nitrogen fixed from the air to grow food through this process now than all of the natural fixations, all the natural reactive nitrogen, which is provided to our soils and around the world.
So it’s a hugely important extra addition to grow our crops. The estimate is about two out of five of us, so two out of every five people you know, wouldn’t be around today without these extra nitrogen fertilisers that come from the Haber process.
So massively important the question now is; in the future can we still go on feeding this growing global population. Maybe 10 billion by 2050. And can we do it in a way where these nitrogen fertilisers are used; the best way possible to avoid the kind of penalties that I talked about in this write up.
To sum up, whether nitrogen is a climate friend or foe, comes down to just how efficiently we use this precious stuff. And how efficiently we use it, comes down to how well we understand it.
Author is a UPSC aspirant, from Raiyar Doodhpathri. He writes regularly for GK.
Disclaimer: The views and opinions expressed in this article are the personal opinions of the author.
The facts, analysis, assumptions and perspective appearing in the article do not reflect the views of GK.