Agriculture Reference
In-Depth Information
0
Cu
10
Cu
Zn
Ni
20
Cd
30
Zn/Ni
Cd
limed
unlimed
40
Relative concentration of adsorbed metal
Figure 7.5
Profiles of surface-applied metals in acid soil, with and without lime and
leached with 0
.
01MCaCl
2
(McBride, 1994). Reproduced by permission of Oxford Uni-
versity Press
precipitation of all four metals resulted in retarded leaching. The attenuation of
Cd
2
+
,
Zn
2
+
and Ni
2
+
leaching could be accounted for with a model allowing for
simple, pH-dependent cation exchange. The results for Cu
2
+
required allowance
for more-selective chemisorption and chelation reactions with highly nonlinear
concentration dependence.
The bioavailability of trace elements is further complicated by differences in
the factors controlling transport to plant roots. These are:
•
desorption or dissolution from the soil solid, which may be slow compared with
transport to roots, and complexation in solution; all of these may be affected
by root-induced changes in the soil, which may both increase and decrease the
solubilities of trace elements;
•
diffusion through the soil solution, especially as complexes with carrier ligands;
•
absorption across the root surface by passive and active transporters, including
for ions complexed with carrier ligands;
•
translocation from root to shoot: cationic trace elements especially may accu-
mulate on and in roots.
7.3.1 MOBILITIES OF INDIVIDUAL TRACE ELEMENTS
In the following sections the biogeochemistries of important trace metals and
metalloids in submerged soils are discussed. They are important either because
of their redox chemistries or because they are particularly affected by soil redox
