Every living thing requires Nitrogen to live. Nitrogen (a gaseous element with the atomic symbol of N) is an essential part of every protein molecule, and proteins are essential to the structure and function of all organisms. All organisms get the nitrogen they need to make their proteins from the environment. Some organisms, like animals, get their nitrogen from eating other things that contain nitrogen. Meat, for instance, is very protein-rich. When we eat meat, we digest the proteins in the meat, breaking them down into smaller and simpler building blocks, called amino acids. We can then use the amino acids to make our own proteins to support our growth and activity. Other organisms, like most plants, absorb nitrogen from the soil. When you put fertilizer on your lawn or garden, a major part of what is in the fertilizer is nitrogen. If you look at the fertilizer bag, it will usually have three numbers on it, like 10-10-10 or 50-0-0. Those numbers represent the percent of nitrogen, phosphate and potash (a source of potassium), respectively, contained in the fertilizer mix. Nitrogen, like I said, is necessary for an organism to make proteins, which allow it to grow and function. Phosphorus (from phosphate) is used to make DNA and RNA, among other things. DNA is the molecule that stores all the genetic information in the organism and RNA is used to help translate that genetic information into new proteins. Phosphorus is also important in root and seed development. Potassium is required for the organism to use energy, use water and many other biochemical functions. The most important of these elements, if any necessary thing is more important than other necessary things, is nitrogen, and therein lies our story.
There is a LOT of nitrogen in our world. Every living thing contains a considerable amount of protein and, therefore, a lot of nitrogen, as part of all the proteins in the organism. On top of that, 70% of the atmosphere is nitrogen. So, given how much nitrogen there is, why is it so important to put nitrogen fertilizer on our lawns and, more importantly, our crops? The answer lies in two places. First, there is what is called the “Nitrogen Cycle”. Most of the nitrogen that is available in the environment is already locked up in the proteins of living things, and it stays there, more or less, until the organism dies. Some nitrogen is excreted as a by-product of metabolism, like in your urine, but it is replaced by nitrogen you take in with food which means it balances out (nitrogen in = nitrogen out). Once an organism dies, however, it decomposes, releasing its nitrogen back into the environment, where it is taken up again by other growing things and they, in turn, hold onto it until THEY die. And so on. That’s why it’s called a cycle—nitrogen is taken up by living things, they die, release the nitrogen and it’s then taken up by other organisms. The result of this is that almost all of the nitrogen available in the environment is already part of some living thing—there is very little nitrogen just lying about, unused. This is why we have to add nitrogen to our plants. It’s because there isn’t enough nitrogen available in the soil to support vigorous and dense plant growth, and even if there is, it won’t be there for very long. Some of the nitrogen in the system is lost as the cycles go on, which is why, eventually, land stops being productive if nitrogen (and other nutrients) aren’t replenished through fertilizers or crop rotation.
Credit: The US Geological Survey
The second part of the answer about why we have to add nitrogen to our soil to promote good plant growth is that, although 70% of the atmosphere is nitrogen (most of the rest is oxygen with just a little carbon dioxide, water vapor and a few trace gasses), the nitrogen that is in the atmosphere isn’t directly usable by most organisms as a source of biological nitrogen. The nitrogen in the air is actually N2, a molecule composed of two atoms of nitrogen bonded together with a very, very strong chemical bond. When the nitrogen atoms are bound to each other with this very powerful bond, they generally can’t be broken apart into individual nitrogen atoms, which is the form of nitrogen used by plants and other organisms for their biochemical needs. The bond is so powerful, that it generally takes something like the power of a lightning bolt to break it. There are, however, some microorganisms, like certain bacteria, that have a special biochemical pathway built-in that allows them to take N2 from the air and break it down to useable forms of nitrogen. These bacteria tend to live in the roots of certain plants, like beans. That is why crop rotation works—corn, for instance, takes a lot of nitrogen to grow, and if you keep growing corn on the same field over and over, without replenishing the nutrients in the soil, the harvest will get worse and worse each year. However, if you rotate corn and beans, the bacteria in the roots of the beans can return some extra nitrogen to the soil one year, while the corn uses it the next year. We still have to fertilize our corn fields, because the corn is planted very densely and it uses a LOT of nitrogen, but rotating with beans helps decrease the amount of fertilizer needed.
So where do we get the nitrogen to put in the fertilizer, if usable nitrogen (N, as opposed to N2) is so hard to find? Well, there are a few places to find nitrogen-rich materials. One is in decaying organic material, like compost. As the organic stuff in the compost rots, it releases nitrogen. Compost is hard to come by on a large scale, though. Most of the time, back in the day, nitrogen was found in animal waste. One of the main functions of your kidneys is to remove nitrogen-containing waste products from your blood, and that nitrogen ends up in urine. The term “urine”, comes from “urea” which is a very nitrogen-rich compound produced in many organisms as a way to get rid of nitrogen, which is toxic in high concentrations in the blood. Anyway, if you’ve ever been in a barn that hasn’t been mucked out in a while, you can easily smell the result—as urea from urine breaks down, it forms ammonia (a compound of hydrogen and nitrogen), and that’s what a barn that needs cleaning smells like (among other charming odors).
So, this is part of the story of nitrogen and the most important person you’ve never heard of. Remember this part, especially the part about how most of the nitrogen used in fertilizers used to come from animal waste, and I’ll finish it up in the next article. It’s a story I like to tell and it’ll be worth the wait.