Geoscience Reference
In-Depth Information
Fig. 18.25 Effect of sodium
adsorption ratio (SAR) on soil
hydraulic conductivity (soil
Burleson; total electrolyte
concentration of irrigation
water = 11 meq/L.
Reprinted from Yaron and
Thomas (
1968
). Copyright
1968 with permission of John
Wiley and Sons
Lagerwerff et al.
1969
), showing that total electrolyte concentration and SAR can
be used to predict the decrease in saturated HC of a soil following percolation with
sodic water.
The decrease in soil hydraulic conductivity can be attributed to changes
occurring in the soil-subsurface matrix. Chen and Banin (
1975
) performed scan-
ning electron microscopy measurements in a sandy soil (6 % clay) and a clayey
soil (55 % clay), the clay fraction in both cases having similar mineralogy. With
an increase in SAR, fine particles were detached from coarse sandy soil, creating a
new matrix arrangement containing a continuous network in the voids. Although
clay movement was more limited in the clayey soil, Chen and Banin (
1975
)
considered that the same mechanism caused the changes in the solid matrix,
indicating possible clay particle migration along the soil profile.
The irreversibility of the salt effect on soil hydraulic conductivity was
emphasized by Dane and Klute (
1977
), who determined the effect of percolating
solution composition on both HC and soil bulk density (Fig.
18.26
). A clayey Weld
soil was tested, with a composition of 24 % sand, 33 % silt, and 43 % clay. The
clay mineralogy consisted of 60 % smectite, 20 % mica, and 20 % kaolin. When
soil samples were subjected to percolation by NaCl solutions with decreasing
concentration and a constant SAR of 40, it was observed that the decrease in total
electrolyte concentration led to a decrease in HC. No changes were observed for a
reference solution (CaCl
2
) with a concentration of 1,000 meq/L and an SAR value
of 0. The composition of the percolating solution affected also the soil bulk density.
The
data presented
in Fig.
18.26
b correspond to soil
samples
leached
with
