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Garden with Insight v1.0 Help: Soil patch next day functions: calculate equilbrium flow between labile P and active mineral P

The equilibrium ratio of labile (free) to active mineral (loosely bound) phosphorus is determined by the phosphorus sorption coefficient or PSP. The use of the PSP is based on the fact that most phosphorus compounds found in soil are relatively insoluble in water, and thus any application of labile P fertilizer tends to precipitate out of the soil water soon after application. The PSP is defined as the fraction of labile to active mineral P after an initial rapid sorption phase has stopped after the application of labile P fertilizer. It depends mainly on the amount of soil weathering, but can be modified by the pH, base saturation, amount calcium carbonate, and amount of clay.

Because this is an equilibrium equation, flow can move both ways. However, if the ratio of labile to active mineral P is such that to reach equilibrium P has to flow from mineral to labile P, the flow is reduced to 10% of what is required for equilibrium because of the insolubility of the phosphorus compounds in the soil.

EPIC Mineral P Cycling
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Updated: May 4, 1998. Questions/comments on site to
Copyright © 1998 Paul D. Fernhout & Cynthia F. Kurtz.