nitrogen, mineral element and inert colourless, odourless, tasteless gas that is extremely useful in both grape-growing and winemaking. Nitrogen gas is an inert constituent of the atmosphere, making up 78% by volume. In its combined forms, nitrogen is an essential element in amino acids, proteins, and enzymes, without which life could not exist. In soil, it is an important constituent of organic matter, from which it is released during decomposition in the form of ammonium ions. Although these ions are taken up by plant roots, much of the ammonium is oxidized by specialist soil bacteria to nitrate ions, which are also absorbed by roots. Ammonium and nitrate compounds are important constituents of many fertilizers.