soil science Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, soil classification, classification and Soil survey, mapping; Soil physics, physical, Soil chemistry, chemical, Soil biology, biologica ...

, mineralization is the

decomposition Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ess ...

(i.e.,

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

) of the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

s in

organic matter Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...

, by which the nutrients in those compounds are released in soluble inorganic forms that may be available to

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

s. Mineralization is the opposite of immobilization. Mineralization increases the bioavailability of the nutrients that were in the decomposing organic compounds, most notably (because of their quantities)

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

, and

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

. Whether the decomposition of an organic compound will result in mineralization or immobilization is dependent on its concentration proportionate to that of the

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

in the organic matter. As a rule of thumb, if the concentration of a specific element exceeds the needs of the decomposer for

biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...

or storage, then it will mineralize.

Ratio of carbon to nitrogen

Whether

mineralizes or immobilizes depends on the

carbon-to-nitrogen ratio A carbon-to-nitrogen ratio (C/N ratio or C:N ratio) is a stoichiometry, ratio of the mass of carbon to the mass of nitrogen in organic residues. It can, amongst other things, be used in analysing sediments and soil including soil organic matter an ...

(C:N ratio) of the decomposing

.R.G. McLaren & K. Cameron ''Soil Science: Sustainable production and environmental protection'' (2nd edition), Oxford University Press, 1996, In general, organic matter contacting soil has too little nitrogen to support the biosynthetic needs of the decomposing soil microbial population. If the C:N ratio of the decomposing organic matter is above circa 30:1 then the decomposing microbes may absorb nitrogen in mineral form as, e. g.,

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

s. This mineral nitrogen is said to be immobilized. This may reduce the concentration of inorganic nitrogen in the soil and thus the nitrogen is not available to plants. As

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

is released during the generation of energy in decomposition, a process called " catabolism", the C:N ratio of the organic matter decreases. When the C:N ratio is less than circa 25:1, further decomposition causes mineralization by the simultaneous release of inorganic nitrogen as ammonium. When the decomposition of organic matter is complete, the mineralized nitrogen therefrom adds to that already present in the soil and therefore increases the total mineral nitrogen in the soil.

References

{{Reflist Soil science Nitrogen

Ratio of carbon to nitrogen

See also

References