The potassium (K) cycle is the biogeochemical cycle that describes the movement of potassium throughout the Earth's lithosphere, biosphere, atmosphere, and hydrosphere.
The potassium (K) cycle is the biogeochemical cycle that describes the movement of potassium throughout the Earth's lithosphere, biosphere, atmosphere, and hydrosphere.
Along with nitrogen and phosphorus, potassium is one of the three major nutrients that plants require in large quantities. [5] Potassium is essential to stomata control in plants and is also essential for muscles contraction in humans. [1]
By weight, K totals to 2.6% of the Earth's crust. [2] Stored in primary minerals (feldspar, biotite, and muscovite), chemical weathering releases potassium into the soil to account for up to 11% of plant demand. [1] Some plants and bacteria also release organic acids into the soil that make K accessible for their use. [1]
Potassium exists in its highest concentrations in the upper most layers of soil, stored in three pools: fixed K, exchangeable K, and solution K. [1] Fixed K accounts for 96-99% of soil K and is stored in feldspar, mica, and illite minerals. [2] Exchangeable K is potassium adsorbed onto clay particles and organic matter and accounts for 1-2% of total soil K. [6] Potassium in soil solution is the most readily available form of K for plants to absorb, but only amounts to 0.1-0.2% of total soil K. [2]
Reserves of potassium exist in ores and evaporites of potassium chloride (KCl) found in Germany, France, Canada, the United States, and Dead Sea brine. [6] [5] An estimated 32 x 106 tonnes (32 Tg) [1] of potassium are mined from the Earth each year, of which 28 x 106 tonnes (28 Tg) [2] are applied to crop fields annually. Potassium is most commonly applied as potassium chloride (KCl), but also referred to as potash and K2O. [6] [5] Application of potassium is necessary in agriculture because the removal of potassium from the soil through plant uptake and crop removal occurs at a faster rate than the replacement through rock weathering. [6] At the current consumption rate, K2O reserves are expected to last 100 years. [7] Potassium depletion in soils can be minimized by leaving crop residues on soils, allowing the plant matter to decay and release their stored potassium back into the soil. [7]
The most abundant ion in plant cells is the potassium ion. [2] Plants take up potassium for plant growth and function. A portion of potassium uptake in plants can be attributed to weathering of primary minerals, but plants can also ‘pump’ potassium from deeper soil layers to increase levels of surface K. [2] Potassium stored in plant matter can be returned to the soil during decomposition, especially in areas of higher rainfall that experience higher leaching rates. [1] Potassium leaching occurs at higher rates than nitrogen and phosphorus, likely because it only exists in the soluble ion form (K+) in the plant. [2] Nitrogen and phosphorus are typically incorporated into large, complex molecules that are more difficult to leach through cell membranes than the small K+ ion. [2] Deciduous plants that lose their leaves will relocate 10-32% of potassium for use in other areas of the plant before abscission. [1]
Some potassium is exchanged between plants and the atmosphere through organic aerosols released from plant leaves. [1] Atmospheric potassium deposition varies from 0.7 to greater than 100 kg ha−1 yr−1 depending on geographic location and climate. [2] Additionally, marine aerosols can evaporate into the atmosphere and return via precipitation. [6]
The hydrosphere is the largest reservoir for potassium, holding an estimated 552.7 x 1012 tonnes (552.7x106 Tg). [2] Leaching and erosion carry 1.4 x 109 tonnes (1400 Tg) yr−1 of potassium in soil solution into groundwater, rivers, and oceans. [2] Some potassium in the atmosphere also enters the hydrosphere through precipitation. Potassium in sediment pore fluids is removed from solution by the authigenic formation of clay, which is then subducted, along with potassium deposits and ocean basalt, to return to the lithosphere. [4]
A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and industrially produced. For most modern agricultural practices, fertilization focuses on three main macro nutrients: nitrogen (N), phosphorus (P), and potassium (K) with occasional addition of supplements like rock flour for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment or hand-tool methods.
Potash includes various mined and manufactured salts that contain potassium in water-soluble form. The name derives from pot ash, plant ashes or wood ash soaked in water in a pot, the primary means of manufacturing potash before the Industrial Era. The word potassium is derived from potash.
A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cycle, the nitrogen cycle and the water cycle. In each cycle, the chemical element or molecule is transformed and cycled by living organisms and through various geological forms and reservoirs, including the atmosphere, the soil and the oceans. It can be thought of as the pathway by which a chemical substance cycles the biotic compartment and the abiotic compartments of Earth. The biotic compartment is the biosphere and the abiotic compartments are the atmosphere, lithosphere and hydrosphere.
Plant nutrition is the study of the chemical elements and compounds necessary for plant growth and reproduction, plant metabolism and their external supply. In its absence the plant is unable to complete a normal life cycle, or that the element is part of some essential plant constituent or metabolite. This is in accordance with Justus von Liebig’s law of the minimum. The total essential plant nutrients include seventeen different elements: carbon, oxygen and hydrogen which are absorbed from the air, whereas other nutrients including nitrogen are typically obtained from the soil.
Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment. In particular, biogeochemistry is the study of biogeochemical cycles, the cycles of chemical elements such as carbon and nitrogen, and their interactions with and incorporation into living things transported through earth scale biological systems in space and time. The field focuses on chemical cycles which are either driven by or influence biological activity. Particular emphasis is placed on the study of carbon, nitrogen, oxygen, sulfur, iron, and phosphorus cycles. Biogeochemistry is a systems science closely related to systems ecology.
The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere, biosphere, lithosphere and the hydrosphere. The pedosphere is the foundation of terrestrial life on Earth.
Soil fertility refers to the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and result in sustained and consistent yields of high quality. It also refers to the soil's ability to supply plant/crop nutrients in the right quantities and qualities over a sustained period of time. A fertile soil has the following properties:
Soil chemistry is the study of the chemical characteristics of soil. Soil chemistry is affected by mineral composition, organic matter and environmental factors. In the early 1870s a consulting chemist to the Royal Agricultural Society in England, named J. Thomas Way, performed many experiments on how soils exchange ions, and is considered the father of soil chemistry. Other scientists who contributed to this branch of ecology include Edmund Ruffin, and Linus Pauling.
The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth. The production of phosphine gas occurs in only specialized, local conditions. Therefore, the phosphorus cycle should be viewed from whole Earth system and then specifically focused on the cycle in terrestrial and aquatic systems.
In agriculture, leaching is the loss of water-soluble plant nutrients from the soil, due to rain and irrigation. Soil structure, crop planting, type and application rates of fertilizers, and other factors are taken into account to avoid excessive nutrient loss. Leaching may also refer to the practice of applying a small amount of excess irrigation where the water has a high salt content to avoid salts from building up in the soil. Where this is practiced, drainage must also usually be employed, to carry away the excess water.
Agricultural pollution refers to biotic and abiotic byproducts of farming practices that result in contamination or degradation of the environment and surrounding ecosystems, and/or cause injury to humans and their economic interests. The pollution may come from a variety of sources, ranging from point source water pollution to more diffuse, landscape-level causes, also known as non-point source pollution and air pollution. Once in the environment these pollutants can have both direct effects in surrounding ecosystems, i.e. killing local wildlife or contaminating drinking water, and downstream effects such as dead zones caused by agricultural runoff is concentrated in large water bodies.
Marine biogeochemical cycles are biogeochemical cycles that occur within marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. These biogeochemical cycles are the pathways chemical substances and elements move through within the marine environment. In addition, substances and elements can be imported into or exported from the marine environment. These imports and exports can occur as exchanges with the atmosphere above, the ocean floor below, or as runoff from the land.
Some types of lichen are able to fix nitrogen from the atmosphere. This process relies on the presence of cyanobacteria as a partner species within the lichen. The ability to fix nitrogen enables lichen to live in nutrient-poor environments. Lichen can also extract nitrogen from the rocks on which they grow.
Seventeen elements or nutrients are essential for plant growth and reproduction. They are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), nickel (Ni) and chlorine (Cl). Nutrients required for plants to complete their life cycle are considered essential nutrients. Nutrients that enhance the growth of plants but are not necessary to complete the plant's life cycle are considered non-essential, although some of them, such as silicon (Si), have been shown to improve nutrent availability, hence the use of stinging nettle and horsetail macerations in Biodynamic agriculture. With the exception of carbon, hydrogen and oxygen, which are supplied by carbon dioxide and water, and nitrogen, provided through nitrogen fixation, the nutrients derive originally from the mineral component of the soil. The Law of the Minimum expresses that when the available form of a nutrient is not in enough proportion in the soil solution, then other nutrients cannot be taken up at an optimum rate by a plant. A particular nutrient ratio of the soil solution is thus mandatory for optimizing plant growth, a value which might differ from nutrient ratios calculated from plant composition.
The copper cycle is the biogeochemical cycle of natural and anthropogenic exchanges of copper between reservoirs in the hydrosphere, atmosphere, biosphere, and lithosphere. Human mining and extraction activities have exerted large influence on the copper cycle.
The boron cycle is the biogeochemical cycle of boron through the atmosphere, lithosphere, biosphere, and hydrosphere.
The chlorine cycle (Cl) is the biogeochemical cycling of chlorine through the atmosphere, hydrosphere, biosphere, and lithosphere. Chlorine is most commonly found as inorganic chloride ions, or a number of chlorinated organic forms. Over 5,000 biologically-produced chlorinated organics have been identified.
The gold cycle is the biogeochemical cycling of gold through the lithosphere, hydrosphere, atmosphere, and biosphere. Gold is a noble transition metal that is highly mobile in the environment and subject to biogeochemical cycling, driven largely by microorganisms. Gold undergoes processes of solubilization, stabilization, bioreduction, biomineralization, aggregation, and ligand utilization throughout its cycle. These processes are influenced by various microbial populations and cycling of other elements such as carbon, nitrogen, and sulfur. Gold exists in several forms in the Earth's surface environment including Au(I/III)-complexes, nanoparticles, and placer gold particles. The gold biogeochemical cycle is highly complex and strongly intertwined with cycling of other metals including silver, copper, iron, manganese, arsenic, and mercury. Gold is important in the biotech field for applications such as mineral exploration, processing and remediation, development of biosensors and drug delivery systems, industrial catalysts, and for recovery of gold from electronic waste.
The iodine cycle is a biogeochemical cycle that primarily consists of natural and biological processes that exchange iodine through the lithosphere, hydrosphere, and atmosphere. Iodine exists in many forms, but in the environment, it generally has an oxidation state of -1, 0, or +5.
The zinc cycle is a biogeochemical cycle that transports zinc through the lithosphere, hydrosphere, and biosphere.