Symbol: N. A nonmetallic element, atomic number 7, atomic weight 14, important as a macronutrient for plant growth. It is essential for the formation of amino acids and the purine and pyrimidine bases, and consequently for protein and nucleic acid synthesis. It is also found in many other compounds, e.g. porphyrins and many coenzymes. Nitrogen is absorbed by roots as the nitrate (N03-
) ion or more rarely as ammonium (NH4+
) or nitrite (N02-
) ions. Deficiency leads to spindly growth and yellowing of the leaves. Soil nitrogen is replenished by various natural processes (see nitrogen cycle
, nitrogen fixation
). It is also boosted by fertilizer applications of such compounds as urea, ammonium nitrate, ammonium sulphate, and nitrochalk. Many high-yielding crop varieties depend on high levels of nitrogen for optimum yields. However excessive nitrogen produces soft tissues with a high water content that are particularly prone to frost damage. Flowering and fruit set may also be reduced at the expense of vegetative growth, while potassium deficiency can be induced by high concentrations of nitrogen.