Geoscience Reference
In-Depth Information
surface waters by industrial discharge of liquid wastes and by salts leached from
upstream fi elds. In some special large regions, the farmers cooperatively organized
and carried out regular or even alternate-year fallowing. It enabled the water table to
fall after each harvest due to evaporation and transpiration from the wild plants that
took over the cultivated fi elds when irrigation was interrupted. However, whenever
soils are already saline, their amelioration is expensive and necessitates a sequence
of several steps of washing and draining an excess of water completely through the
root zone. The main problem is where to conduct and dispose of the saline drainage
water. Because downstream governments are usually against transferring salty
water into one or more nearby upstream riverbeds, the curing of soils suffering sali-
nization is complicated and expensive. Inasmuch as salinity reduces yields on about
20 % of all irrigated soils, its impact is certainly not negligible considering that
about 12 % of the global population is still undernourished (FAO statistics for
2010-2012).
If we say that soil is something like a living organism, then we must admit that
the degradation and worsening of soil properties are similar to a serious illness of
the soil. Moreover, an ill or sick soil equals starving, and starving means losing
battles and fi nally the loss of a war. All such circumstances have been frequently
caused by the abrupt change of some of the natural conditions in the past, but we
realize additionally that various activities of human society also contributed. And no
doubt, all shall contribute in the future. Our aim is to understand how soil is the
decisive factor in the environment.
14.2
The Death of Soils
Water is muddy during a fl ood, and when the high water sinks back into the river-
bed, the surrounding fi elds and meadows are covered by a fi lm of sludge - a dark
gray, fl imsy almost transparent shroud extending over and between thin branches of
shrubs, blades, and straw as well as the soil surface. The constituents within these
shrouds originated upstream, were carried along in the fl ood, and are no longer pres-
ent upstream. What is really missing upstream? The answer is surface soil eroded
by water from the place of its origin. It is as if the soil dies. Rainwater fl owing on
the slope dislodges and carries soil particles down the slope. Great volumes of this
concoction of water with silt and clay particles are transported to the plain below the
slope and eventually into the mainstream of a brook and river.
Soil water erosion
is caused by water fl owing in a thin sheet on the slope of land
being attacked by raindrops. When the rain intensity is higher than the infi ltration
rate, the excess water remaining on the land surface forms a very shallow water
layer having a very small slope that causes a downhill fl ux of this excess water. The
falling water drops look like a strong bombardment, the soil aggregates are mechan-
ically broken into elementary silt and clay particles, and the released particles are
smashed around. These elementary particles are carried away even by a small fl ux
of surface water because they are each very tiny and substantially lighter than the
