why is nitrogen important to plants and animals

Nitrogen (N) is one of the building blocks of life: it is essential for all plants and animals to survive. Nitrogen (N2) makes up almost 80% of our atmosphere, but it is an unreactive form that is not accessible to us. Humans and most other species on earth require nitrogen in a Бfixed,Б reactive form. Reactive nitrogen is necessasry for the food production process. Until the discovery of the Haber-Bosch process in the early 1900s, we only had access to naturally occurring sources of reactive nitrogen (such as manure and guano) for food production. The Haber-Bosch process--an industrial process through which we can fix reactive nitrogen--has allowed food production to keep up with the growing human population, but at a cost to the environment.

Today, humans create over 2 times as much reactive nitrogen as nature. In contrast, human activity contributes just 5-10% of CO2ббemissions. Much of this reactive nitrogen has accummulated in the environment, where it causes a series of negative impacts to human and ecossytem health. Major sources of this reactive nitrogen include agriculture and the burning of fossil fuels. This nitrogen pollution causes profound environmental impacts, including smog, acid rain, forest dieback, coastal Бdead zonesБ, biodiversity loss, stratospheric ozone depletion and increased greenhouse gases.

It also affects human health, including respiratory disease and an increased risk for birth defects.
Nitrogen forms an essential part of amino acids and nucleic acids, both of which are essential to support of all life. Molecular nitrogen in the atmosphere cannot be used directly, whether by plants or animals, but needs to be converted to other compounds, or вfixedв, in order to be used by life. So nitrogen is an essential nutrient for plant growth and therefore very important for food production. In addition to its role in supporting life, many industrially important compounds, such as ammonia, nitric acid, urea and cyanides contain nitrogen.

In the early part of the 19th century, the use of nitrogen from droppings of sea birds (guano) on small islands off the Peruvian coast increased, but the guano deposits were rapidly depleted. For this reason, it is understandable that the English chemist, Sir William Crookes, claimed in a widely published lecture in 1898 that without a new source of nitrogen fertiliser famine would be inevitable within two to three decades. Crookes then called on all chemists to find way to fix nitrogen chemically from the unlimited reserves in the air. Several attempts were made, and in 1908 Fritz Haber patented his synthesis of ammonia from the elements, nitrogen and hydrogen.

The equipment used by Haber was later scaled up to a pilot plant and further to a commercial plant. By 1930, the amount of Haber-Bosch nitrogen was already equal to that from all other sources put together. However, the real increase in nitrogen fertiliser production took place between 1960 and 1970. The use of nitrogen fertilisers has played an essential role in the more than doubling of the global food production (and the world population) in the past 50 years. Of course, industrial nitrogen fixation has also led to large surpluses of nitrogen in agriculture.

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