Geoscience Reference
In-Depth Information
Also:
Log C
(meq/l)
= 0.955 + 1.039
log EC
(mmhos/cm)
Relations between conductivity and osmotic potential
Approximately,
Po
= -
k·EC
with Po in atmospheres and EC in mmhos/cm.
k
is then a coefficient with the value:
0.35 for NaCl
0.30 for Na
2
SO
4
0.28 for MgSO
4
The osmotic potential in bars is approximately
y
≈
5.6
×
10
-4
·TDS
mg/l
(this actually depends on the dissolved ions!).
Relation between TDS and osmotic potential
13.1.4 Essential Concepts
Salinization
is the occurrence of salts in the soil solution. A soil
is considered saline—more correctly, a horizon is
salic
—when the
saturated-paste extract has an EC higher than 15 dS m
-1
(WRB) at
certain times in the year. The threshold is lowered to 8 dS m
-1
if the pH
is higher than 8.5 (WRB). But these values are quite high; Americans,
followed by other countries, have lowered the threshold to 4 dS m
-1
(Rengasamy 2002).
The predominant salts in the soil solution are NaCl, Na
2
SO
4
and, at
times, NaNO
3
.
Sodization
is enrichment of the exchange complex with exchangeable
sodium. A soil is
sodic
when the percentage of exchangeable sodium (
ESP
defined earlier) is greater than 15. But the phenomena of degradation of
structure (see below) sometimes occur at lower values.
Alkalization
is rise in pH linked to the presence of excessive carbonates
or bicarbonates, especially Na
2
CO
3
and NaHCO
3
. These are salts of a
strong base and a weak acid, the dissociation of which in water results
in an alkaline solution. Theoretical calculations show that the pH can
rise to 12.
Definitions
