NPK is an acronym for Nitrogen (N), Phosphorus (P), and Potassium (K), the three things plants need to prosper: Nitrogen for chlorophyll production, Phosphorus for healthy roots, and fruit set, and potash (which provides Potassium) for overall plant health and disease resistance. Conventional soluble NPK fertilizers are made in factories by combining natural gas with nitrogen and oxygen from from the air. They are not permitted in organic or Biodynamic agriculture. See nitrous oxide, a greenhouse gas and by-product in the production of conventional NPK fertilisers.