Publication date: 1 September 2018
Source:Geoderma, Volume 325
Author(s): Christoph Weihrauch, Christian Opp
There has been much soil phosphorus (P) research in the last decades, but few basic publications exist summarizing the current state of knowledge on ecologically relevant P forms and their reactions in soils. The present paper aims at giving such a literature overview. The major P forms occurring in soils are presented. Organic P results from biogenic processes when organisms take up P from the soil. After their death, this P is returned into the soil and has to be mineralized before the next uptake. Mineralization intensity depends on the concentration of dissolved inorganic P in the soil solution. Only this soil P fraction can be taken up by plants and microorganisms and enter the food chain. Thus, it is critical for ecosystem nutrition. Dissolved P is highly affine for binding to the soil matrix and strives for equilibrium with bonded P forms. On the one hand, there is sorbed P , regularly forming quickly and being easily exchanged back into the soil solution. Sorbed P strongly depends on which and how many sorption sites a soil offers. Some of these sites are not easily accessible. Thus, P needs time to be sorbed there and is slightly soluble afterwards. This fraction is termed “occluded P ”. It is considered fixed and not bioavailable for long times. On the other hand, there is mineral P , resulting from the precipitation of P anions and metal cations when the soil solution is oversaturated with these ions. The stability of mineral P depends on its degree of order, amorphous phases being less stable than highly crystalline minerals. Organic, sorbed and mineral P are tightly interconnected with dissolved P and strive for equilibrium with it. Due to changes in temperature, precipitation and vegetation/edaphic patterns such equilibrium is hardly attained and soil P reactions must dynamically adjust to present conditions.
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Source:Geoderma, Volume 325
Author(s): Christoph Weihrauch, Christian Opp
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