The cycling of macro- and micronutrients is an essential function of soils. Mineral weathering generates a slow but constant source of elements made available for biochemical cycles.  Soils are biochemical reactors, where numerous organic and inorganic compounds are  decomposed and transformed so that the nutrients become again available for soil biota  and biomass production. The engine driving this reactor is the myriad of organisms living  in soil and taking profit from the energy stored in plant residues. Some part of it, however,  is protected from decomposition for quite a long time so that soils act as a substantial  carbon pool. An important feature is the ability of soil to retain nutrient within the root zone and to avoid leaching towards groundwater or emission to the atmosphere where the same  nutrients might be harmful (e.g. NO3 in groundwater or N2O in the atmosphere).