| dc.description.abstract | Infiltration rate (IR) is the volume flux of water
flowing into the profile per unit of soil surface
area (Parr and Bertrand, 1960) when the soil is
subjected to a shallow depth of ponding at the
surface (Ghildyal and Tripathi, 1987) or when the
water supply is not limiting (SSSA, 1975). IR is
generally expressed in cmlh (Schwab et al,
1981). The term infiltration capacity is frequently
used in hydrology to refer to IR (Ghildyal and
Tripathi, 1987). It is generally observed that
under continued ponding, IR is high at the
beginning, decreases rapidly and then more
slowly until it approaches a constant rate
asymptotically. Infiltration rate affects many
aspects of hydrology and agriculture including
runoff and water content of the soil, and is related
to evapotranspiration (Marshall and Holmes,
1988).
Most soil profiles are differentiated into horizons
thus, water distribution during infiltration is not
uniform. Examples include a loose ploughed
layer overlaying compact subsoil and a surface
crust with higher bulk density and lower
hydraulic conductivity (HC) than the underlying
soil mass. Where a coarse layer overlays a finetextured
layer, the initial IR and the final IR are
controlled by the coarse and the fine-textured
layer respectively (Hillel, 1980). It has been
conclude that in such a case, it is the layer of the
lowest HC that controls the process of infiltration
(Hillel, 1982).
As in the case of a crusted soil where the HC of
the surface layer is lower than that of the subsoil,
the crusted layer determines the initial IR.
The IR values of crusted soils or soils with a seal
depend on the HC of the crust or seal (Shainberg
and Levy, L996). For this reason some
researchers have tried to measure the HC of soil
surface seals. Mclntyre (1958) found that the HC
of the upper and lower layers of the seal of a
sandy loam soil were 2000 and 200 times lower
than the HC values recorded for the undisturbed
soils. Bresler and Kemper (1970) measured a HC
value of 1.5 x 10-a mm,/sec in the upper 2-3 mm
of a sealed clay loam soil. However, the crust is a
very thin layer and it is very difficult to
determine its HC. Consequently, IR is widely
used to characterise water entry into the soil,
particularly when seal formation is involved
(Shainberg and Levy, 1996). Kazman et al.
(1983) studied the effect of
exchangeable sodium percentage (ESP) on IR
and seal formation of 4 smectitic soils of varying
textures using distilled water. Infiltration rate was
found to be highly sensitive even to low levels of
ESP. Shainberg (1985) concluded that seal
formation depends on the electrolyte
concentration of the applied water. Furthermore
when sufficient electrolye is provided with
water, chemical dispersion is low (Aggasi et al.,
1981). The effect of clay content on the IR of
soils was studied by Ben-Hur er a/. (1985). Soil
samples with clay contents between 3 and 607o
were chosen from smectitic and non-semetitic
soils. For both categories of soils, soils with 10 -
3O7o clay were most susceptible to seal formation
and had the lowest IR. The objectives of this
study were (1) to compare the IR and HC of 3
salt-affected soils and (2) determine the influence
of organic matter, soil texture and bulk density on
IR and HC of the salt-affected soils. | en |
