Available Cd content of salt-affected and normal soils of Halastra-Kalohori area

A survey was conducted in order to evaluate the levels of available (DTPA extractable) Cd in
salt affected and normal soils of Halastra−Kalohori area, located in N. Greece. In this area,
phosphogypsum (PG) (a byproduct of P fertilizer industry, occasionally enriched with Cd) has
been used as amendment for the salt affected soils, for at least 20 years until 2000. The area
is about 6300 ha, and 4500 ha were cultivated with rice. Soil samples were collected from 632
points and four depths (0−25, 25−50, 50−75, 75−100 cm), during 2003 and 2004. All soil
samples were analyzed for particle size distribution, pH in the paste, electrical conductivity of
the saturation extract (ECe), water soluble Na, Ca and Mg, cation exchange capacity (CEC)
and exchangeable Na. The sodium absorption ratio (SAR) and exchangeable sodium
percentage (ESP) were calculated. The 632 soils were characterized as salt affected (saline,
saline−sodic, sodic) or normal, using the values of EC, SAR and ESP, and pH. In addition, the
soil samples collected from the 0−25 and 25−50 cm depths were analyzed for DTPA
extractable Cd and Olsen P. All soils were alkaline in reaction. In most of the cases,
concentrations of DTPA extractable Cd in the 0−25 cm depth were higher than in the 25−50
cm depth and the mean values differed significantly (p < 0.001). For both depths,
concentrations of DTPA extractable Cd were higher for salt affected than normal soils and the
mean values within each depth differed significantly (p < 0.001). This could be attributed to
the use of PG as soil amendment. In addition, a significant and positive relationship was
obtained for DTPA extractable Cd and ECe (r = 0.31, p < 0.001). However, DTPA extractable
Cd ranged at levels similar or lower to those reported in the literature for cultivated soils with
high P fertilization, in almost all cases. This is something to be expected since 80 % of all
soils were sufficient or over−fertilized with P (Olsen P > 15 mg kg−1). A significant and positive
relationship, obtained for DTPA extractable Cd and Olsen P (r = 0.47, p < 0.001), supported
the conclusion that the source of DTPA extractable Cd could also be traced to the long−term
P fertilization. Concentrations of DTPA extractable Cd were significantly (p < 0.001) correlated
with certain soil properties that affect Cd availability to plants, such as pH (r = −0.26), clay
content (r = 0.22) and CEC (r = 0.26).