Immob i
The Phosphorus "cycle"
Organic
phosphorus
l ization
n
g
"
Mineralization
Phosphorus
in apatites of
soil parent materials
Solution
phosphorus
H2PO-4
Fixation
Solution
Calcium phosphates
Clay-adsorbed
phosphorus
Iron and aluminum
phosphates
"
L
e
a
c
h
i
Weathering
PERCENTAGE DISTRIBUTION
100
Relatively available
phosphates
Fixation by hydrous
oxides of Fe,
Al, and Mg
50
si Rea
lic c
at tio
e n
m w
in ith
er
al
s
Fixation mostly
as calcium
phosphates
Chemical
fixation by
soluble Al, Fe, and Mn
0
4.0
5.0
6.0
SOIL pH
7.0
8.0