Phosphorus
(P) Availability
P
is held in the soil in different pools which vary in
their ability to release P to the soil solution in a
plant available form, as
represented by the schematic representation below (adapted from
IARC, Rothamsted).
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The
schematic diagram above highlights the complexity of soil P chemistry.
Typically, soils can only hold around 1% of their total P in a water-soluble
form in the soil solution. Excess water-soluble P is quickly adsorbed
into the labile and then the non-labile pools rendering it less
available, whereas P from RPR's (such as Gafsa) are held in the
more readily available part of the labile pool from where it is
transferred back into soil solution as and when required.
This
situation is represented in the schematic diagram below, which highlights
the phased release nature of RPR as opposed to the large initial
- but unsustained - release of P from water-soluble TSP.
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Phosphorus (P) Efficacy >>
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