Geoscience Reference
In-Depth Information
Fig. 18.8 Effect of varying application of CaSO
4
and CaCl
2
on the relative hydraulic
conductivities of Golan (noncalcareous) and Nahal Oz (calcareous) soils, as a function of
cumulative effluent volume (Shainberg et al.
1982
). Copyright 1982 Soil Science Society of
America. Reprinted with permission
solution, or due to the impact of raindrops. Dispersion of soil clays may lead to the
clogging of pores beneath the surface, forming a layer of low permeability. Seals
(\2 mm) that form have a greater density, higher shear strength, finer pores, and
lower permeability than the bulk soil. Addition of gypsum to the soil surface
increases electrolyte composition of the incoming water, preventing the break-
down of soil aggregates and decreases in pore size.
The effect of addition of mined gypsum (G) and the industrial byproduct
phosphogypsum (PG) on infiltration rates was studied by Levy and Sumner (
1998
).
It was found that PG is more effective than G in enhancing water transmission, and
that infiltration rates depend on the amount and method of application of PG, and
on cumulative rainfall (Fig.
18.9
).
Aggregation status of the soil-subsurface system is a main factor in controlling
water transmission properties of the soil-subsurface system. In general, the active
pores conducting water are of micrometer scale and are enclosed in aggregates
formed by heterogeneous conglomerates in which submicron clay particles are
associated (Ahuja et al.
1989
). A laboratory study by Lebron et al. (
2002
)
examined changes in aggregate size and geometry of sodic soils amended with
gypsum, as reflected in soil water transmission properties. An increase in ESP due
to gypsum application was associated with a decrease in larger size aggregates and
