Colourless, odourless and tasteless gas (N = Nitrogenium), which with 78% volume is by far the largest component in the air. The German designation reminds us that nitrogen "suffocates" (extinguishes) flames. The nitrogen compounds amino acids, alkaloids, ammonium (compound with hydrogen, the most common starting material for fertilizers), enzymes, nitrates and saltpetre are of great importance. 95% of nitrogen in the soil is found in the form of organic compounds (Norg) in humus formed from dead plant and animal material, in living root mass and in soil organisms. A maximum of 5% is mineral-bound nitrogen (Nmin) already available to plants in the form of ammonium (hydrogen compound) and nitrate = saltpetre (oxygen compound). However, the organic nitrogen compounds are not available for higher-quality plants. They must first be converted into ammonium and nitrate by bacteria, which thus play an important role in plant growth. Nitrates are absorbed preferentially by the roots, which are responsible for the formation of cell protein and chlorophyll during photosynthesis.