4 All animals produce waste nitrogen in the form of a nitrogen-containing compound called urea. This is removed from the body during excretion. It will either evaporate or be broken down by bacteria. Nitrogen-containing compounds are very soluble and rainwater may wash them into rivers, where they may cause pollution problems. 5 Bacteria involved in decomposing waste and dead material release nitrogen from its compounds, forming gas that can escape to the atmosphere, thus completing the cycle.
Animals produce urea intheir waste products.
Urea decomposes to ammonia and carbon dioxide and may be lost to the air or dissolved inrainwater where it becomes a natural fertiliser. Gaseous nitrogen makes up three-quarters of the atmosphere. This inert nitrogen is not available for plant use and plays no part in the nitrogen cycle. Nitrogen is fixed in the atmosphere during lightning. Nitrogen is dissolved in rainwater to form dilute nitric acid, natural acid rain that provides some of the nitrogen fertiliser requirements of plants.