Living on air I 13 Keeping the nitrogen cycle in balance with supplementary nitrogen N Almost 80% of the Earth’s atmosphere is made of gaseous or atmospheric nitrogen. To make atmospheric nitrogen suitable for consumption, it has to be “fixed.” In nature, nitrogen fixation takes place in the atmosphere and in the soil. Atmospheric nitrogen can be fixed in the atmosphere by lightning strikes, for example. Rain then carries it to the soil in the form of nutrient nitrogen. In the soil, bacteria fix atmospheric nitrogen. N Nutrient nitrogen disappears when crops are removed from the land. In addition, natural processes cause it to disappear into the air, soil and water. To meet the world’s growing demand for food, early twentieth-century scientists developed a method for producing nutrient nitrogen. The fixation of atmospheric nitrogen now occurs on an industrial scale, with mineral fertilizers as the product. Together with the nutrient nitrogen produced by natural fixation in the atmosphere and soil, they make an unbeatable combination.
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