Cropping Systems: Applications, Management and Impact

Phosphorus Dynamic in the Soil-Plant System ... 47

A Conceptual P Model

Abundant research shown that physical fractionation by particle size is
useful for studying chemical structure of soil organic matter and its dynamics.
Soil organic fractions, and its P contents, within the sand fraction are allocated
to the labile pool and soil fractions in silt and clay fractions to the intermediate
and passive pools (von Lützow et al., 2007; Suñer et al., 2013). On the other
hand, inorganic minerals of the coarse fraction can be considered a passive
pool of P, while the P present in the fine fraction represents an active pool.

Po, organic P; Pi, inorganic P; Pa, available P; MOM, mineral associated organic
matter; POM, particulte organic matter; Flows, a) weathering and physico-
chemical processes, b) humification, c) mineralization of SOM fractions, d)
physico-chemical equilibrium, e) P-uptake by plants; f) recycled P.

Figure 7. Conceptual model of Phosporus pools and flows in soil-plant systems.

We propose a conceptual model to identify P changes in soils with
different textures (Figure 7). Soil organic fractions and their P-content within
the sand fraction are inside the labile pool, whereas those within the silt and
clay fractions are inside the intermediate and passive pools. Inorganic minerals
of the coarse fraction can be considered a passive pool of P, while P in the fine

Po

Pi

Po

Pi

Pa

Phosphorus

Form

Organic

Inorganic

Size Fraction

Sand

MOP

Clay-silt

MOM

Fine Coarse

e

f

b

c

d

a

c