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Magnesium hydrogen orthophosphate (CAS 7757-86-0) is an inorganic magnesium and phosphate salt, and therefore a ready biodegradation test is not applicable. Data on photodegradation are not available. The substance is considered non-volatile and a significant release to the atmosphere is not anticipated. When released to the environment a dominate distribution in water and transportation between water and soil is most likely. The water solubility of the substance is inversely related to the pH value. In release into water the substance dissociates to phosphate species and magnesium ions. Both ions are generally abundant natural elements that are ubiquitous in the aqueous and terrestrial environment.

Magnesium is among the most abundant elements and is an essential nutrient for higher plants, algae and animals. Ionic magnesium is highly mobile on one hand, and on the other hand it can adsorb to the surface of clay and organic matter becoming immobilised in natural soil (Mikkelsen 2010, Schulte 2004). The mobility in soil strongly depends on the cation exchange capacity (CEC) of the soil. Soils with a high CEC, soils with more clay or organic matter, will hold more magnesium caused by a higher total amount of exchangeable cations that the soil can adsorb. As a result, magnesium and the other cations are plant available. The actual CEC of the soil is also depended on the pH of the soil, and thus will increase with an increase in pH (Cornell University Cooperative Extension, 2007). Therefore, Magnesium will become more available with increase of soil pH.

Phosphorus is required by all living plants and animals. Phosphorus containing compounds are essential for photosynthesis in plants, for energy transformation and for the activity of some hormones in both plants and animals (Cornforth I.S., 2008). The Phosphate ion can occur in three states of protonation, which is pH dependent. In soil H2PO4 and HPO4 are the dominant species for pH values of 4.5 – 6.2, which are occur normally in soil. This is the form in which phosphorus is used by plants. Precipitation-dissolution and sorption-desorption processes control the concentration pf phosphate ions in solution. Phosphate ions are mainly immobilised in soils by adsorption to solid matter or by reaction with aluminium or iron to aluminium- and ironphosphates (Cornforth 2008).

References:

Cornell University Cooperative Extension (2007) Cornell University Agronomy Fact Sheet # 22: Cation Exchange Capacity (CEC)

Cornforth I.S. (2008) The fate of phosphate fertilizers in soil. New Zealand Institute of Chemistry. II-Chemicals and Soils-D-Phosphate-2 (with reference to: Dahal 1977; McLaren and Cameron 1990; Syers and Cornforth 1983)

Dahal, R.C. 1977. Soil organic phosphorus. Advances in Agronomy. Volume 28, 83-117.

McLaren, R.G.; Cameron, K.C. 1990. Soil Science, an introduction to the properties and management of New Zealand soils.

Mikkelsen R (2010) Soil and fertilizer magnesium. Better Crops 94:26–28

Schulte E. E. (2004) Soil and Applied Magnesium, University of Wisconsin-Extension, Understanding Plant Nutrients, A2524

Syers, J.K.; Cornforth, I.S. 1983. Chemistry of Soil Fertility. Read at the New Zealand Institute of Chemistry Annual Conference, Hamilton.