Abstract:
Phosphorus (P) sorption in soils is a key
process governing its availability to crops.
There has been scanty information available on
the P sorption characteristics of calcare-
ous soils of Western Azarbaijan Province, Iran
. In this study, P sorption characteristics
and their relationship to soil properties were
determined in 36 soil samples belonging to
15 agricultural soil series located in the sout
h of Urmia, Western Azarbaijan Province.
Total CaCO
3
contents ranged from 10 to 48.5%. Active CaCO
3
contents ranged from 1.7
to 20% and were significan
tly related (r = 0.61,
P
<0.001) to the total CaCO
3
of the soils.
NaHCO
3
-extractable P contents ranged from 4 to 38 mg P/kg soil. The amount of P
sorbed by the soils differed among various soil
series. The results sh
owed that equilibrium
solution P concentration (EPC) was lower
(<0.2 mg/L) than the requirement for most
crops. The amount of P adsorbed by the soil
s at 0.2 mg/L EPC ranged from 5 to 114
mg/kg soil. The phosphate adsorption was well described by the Freundlich (r
2
= 0.96)
and Langmuir (r
2
= 0.88) isotherms. The Lang
muir maximum adsorption (X
m
) and
Freundlich coefficient (a
F
) estimated from Langmuir and Freundlich equations ranged
from 127 to 238 mg P /kg soil and from 43 to 211 mg P/kg, respectively. Soil clay content
was significantly related to the soil P sorption indices, P
0.4
(P sorbed at 0.4 mg P/L, r =
0.40,
P
<0.01), PBC (P buffering capacity, r = 0.54,
P
<0.001), a
F
(r = 0.48,
P
<0.01), and X
m
(r = 0.40,
P
<0.01). Total CaCO
3
and active CaCO
3
were found to be less important factors
affecting P adsorption
