Of the nearly 20 substances that plants take from the soil and air to live, nitrogen is perhaps the most mutable. It leeches through soil and dissipates easily. It must travel in compounds--nitrates, nitrites and ammonia--because it needs other atoms to make a molecule. Nitrogen, however, is the nutrient with the greatest effect on plant growth.
Nitrogen's natural state is as a gas in the atmosphere. It finds its way into the soil through organic matter. Plants and animals that consume nitrogen during their lifetimes release it as nitrites and nitrates as they decompose in soil.
The Ohio State University Extension says nitrogen is necessary for hearty plant growth. The Fertilizer Institute says it plays a major role in the formation of chlorophyll and provides a building block for plant protein. Plants that have an adequate supply of nitrogen are deep green, grow quickly, develop a healthy structure and flower or fruit well. Unfortunately nitrogen must join with other substances to become a part of the soil; this "immobile" nitrogen cannot be absorbed by plant roots.
Animal and bird manure provided the first nitrogen fertilizer. Unfortunately, heavy farming used more nitrogen than was in the soil; eventually the soil "wore out" and produced less. In 1909, Scientific American reports. Fritz Haber, a German chemist, heated nitrogen and hydrogen under pressure to create anhydrous ammonia, a chemical that provided nitrogen in a form that could be absorbed by plant roots. Ammonia synthesis lead the way to the development of synthetic nitrogen fertilizer that formed the basis of the 20th century's Green Revolution.
In addition synthetic forms of nitrogen fertilizer, organic fertilizers composed of composted biosolids contain nitrogen. The Colorado State University Extension reports that the nitrogen in many organic fertilizers is immobile; high-carbon organic compost needs to be supplemented with sources of nitrogen to make it available to plants. When balanced correctly, organic fertilizers can improve soil as well as provide nitrogen and other nutrients.
Extra helpings of nitrogen, whether synthetic or organic, can be bad for the environment, according to the Scientific American review of the 100th anniversary of Haber's discovery. Excess nitrogen leeches through soil as nitrates into aquifers and runs into streams, rivers and lakes. It encourages algae bloom and leads to decreased aquatic oxygen, killing aquatic life and contributing to climate change.