Healthy plants have a lot of nitrogen in their above-ground parts, usually around 3 to 4 percent. This is much more than other nutrients like carbon, hydrogen, and oxygen. Nitrogen is very important for plants because it helps them make chlorophyll, which is how they use sunlight to make sugar from water and carbon dioxide. Nitrogen is also a key part of proteins, which are like the building blocks for plants. Without proteins, plants can’t survive. Nitrogen is also used to make compounds that help transfer energy in cells and to make DNA, which is what allows plants (and all living things) to grow and reproduce. In short, nitrogen is essential for life as we know it.