So, I recently watched a video regarding the first synthesized fertilizer, and I thought it was pretty interesting that farmland was basically screwed if they didn’t figure out how to get more nitrogen into dirt.
But then I thought about it, I was taught that plants make the bulk of themselves out of carbon, which they absorb from the air in carbon dioxide. Why is the same not true with nitrogen? Our atmosphere is a little more than 2/3rds nitrogen after all.
I tried looking it up, but the result was basically “Because nitrogen in the atmosphere is in a gaseous form” but that wasn’t really helpful.
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Because they simply do not have the [required biological machinery](https://en.wikipedia.org/wiki/Nitrogenase). Animals and fungi also don’t have it, luckily some bacterial cultures do so they basically do the nitrogen binding for the entire rest of the ecosystem(ignoring industrially produced fertilizers).
Similarly, all the vitamins, they are classified as vitamins because your body needs them, but can’t produce them on it’s own. You have to consume them from your food.
bacteria evolved the ability to do this first, and are so good at it, that there is little evolutionary advantage to be gained by any plant that managed to evolve the ability. the plants don’t *need* to fix nitrogen. They already have mutualistic relationships with microbes that do it for them.
Imagine nitrogen is like tape, and it’s easy to stick it onto something.
Normally, when you apply tape to something, you can do a little bit of work to remove the tape. But imagine two pieces of tape stuck to each other– Nearly impossible to separate, at least without a lot of very careful work.
The particular form of nitrogen in the air, N2, is two nitrogen atoms stuck together, and like the tape, and they’re very hard to separate.
Many/most plants rely on _nitrogen fixation_, which is a collection of processes for separating the two nitrogen atoms and sticking them to something else that’s easier to for the plant to work with/consume.
Nitrogen in the air is in the form of N2 and it rather stable because it has a triple bond between the N atoms. It takes more energy to break the N2 triple bond and bacteria have been selected to do that energy requiring step. It gets broken down in the soil by bacteria in to amino-compounds which are more easily reactive and accessible for the plant. It’s all governed by thermodynamic. For the plant, it is easier to take up N from the soil because it is usually broken in to molecules that are only single bonded to it and N has an extra pair of unpaired electrons that plants access much more easily and with a favorable thermodynamic.
For the same reason we can’t eat oxygen. The leaves are not designed to absorb nitrogen in its airborne form
Along with what others have said, here’s an analogy. We need to breathe oxygen. H2o and co2 both contain oxygen but we definitely can’t breathe them as our supply of oxygen. Technically having the atom doesn’t mean it can be used the same.
Was the video about Fritz Haber? Did Sabaton lead you there?
Man the answers are all over the place on this one. Maybe because what your asking sounds more like a philosophy question . Plants can absorb nitrogen from the air btw. I’ll assume you are asking why they can’t turn it into protein. The short answer is they absolutely could but lack the genes for it. Why can’t you turn sunlight into sugar? Why can’t we breathe under water? The answers to questions like this is that we don’t know for sure. Evolution took the paths it took and here we are. Maybe it’s not worth the bother to plants when they get enough nitrogen from bacteria or lightning strikes. Another part of your question involved farming. Farmed plants are not natural. We use fertilizer to increase the yield, but those plants will still grow without fertilizer.
Atmospheric nitrogen is more or less inert; two atoms form a N2 molecule that is very stable; the bond between them is well balanced. Nitrogen in the form of nitrates in soil will easily break free in water solutions and form N^2- ions; plants can incorporate those easily into more complex molecules since it is unstable and needs to form compounds with something.
You know how cling wrap sticks to itself really well? And if you pull out a lot of cling wrap, it is almost impossible to pull all of it apart at the same time? The Nitrogen in air (N2) is similar to that. It sticks together very strongly. Nitrogen sticks to itself about 3 times stronger than it sticks to a single Hydrogen. It takes a lot of energy to break apart N2, so plants instead get the Nitrogen from sources where it is bonded more weakly with other atoms, like nitrates (bonded to Oxygen) and ammonia (bonded to Hydrogen).
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