Geoscience Reference
In-Depth Information
masks at the carnival and to the long-lasting hangover experienced by the partici-
pants of the carnival?
If the farmers wish to ameliorate sodic soils and prevent the loss of soil structure,
they must introduce a higher concentration of calcium into the soil. The high Ca
2+
concentration required to replace the exchangeable Na
+
in exchange positions is
achieved by the application of gypsum. The Ca
2+
cations in gypsum (CaSO
4
.
2H
2
O)
displace and release the Na
+
on exchange positions. The released Na
+
reacts with
sulfate (SO
4
2−
) to form sodium sulfate (Na
2
SO
4
), which is a highly water-soluble
compound that is easily leached from the soil. Gypsum is therefore very useful
when soil structure deteriorates because of high sodium.
Up to now we have been focusing on the harmful action of inorganic salts con-
taining sodium. Other inorganic salts containing monovalent cations like NH
4
+
and
to a much lesser extent K
+
also create similar yet somewhat less harmful situations.
The total effects associated with the behavior of these and a few other specifi c cat-
ions frequently observed in arid and semiarid soils of agricultural regions justify the
backbone of ameliorative uses of irrigation. Research leading to the desired control
of specifi c solutes within such regionally irrigated soils is one of the many primary
goals of soil science.
Nowadays however even in mild climatic regions, intensive agricultural cultiva-
tion leads to water pollution, to the salinization of water, or to pollution by other soil
structure-breaking compounds.
7.7
Inhabitants of Soil Pores
Soil pores hold more than just water containing solutes and chemicals and air con-
taining water vapor, CO
2
, and other gases. They are also inhabited by various types
of living bodies, many of which are so small that they only can be seen under a
microscope as we have shown in Chap.
4
. Living microorganisms make up 60-80 %
of the majority of living fl ora and fauna that occupy soil pores. The root systems of
plants represent 5-15 %, while macro- and mezzo-organisms account for the
remaining percentages of soil life. The amount of bacteria living in soils is compa-
rable to those occupying water between continents and is substantially higher than
those above the pedosphere of the continents.
Soil bacteria form natural communities infl uencing the very existence of soil and
its physical properties, the use of nutrients via the root system of plants, and gener-
ally the soil fertility, as some species decompose the remnants of animal bodies and
of dead parts of plants. The useful plant nutrients are thus released. Bacteria living
in close proximity to plant roots are called rhizobacteria. The term comes from the
Greek
rhiza
meaning root. Rhizobacteria form symbiotic associations with plants
through their activity in the rhizosphere - the space where roots penetrate the soil.
This relationship is mutually benefi cial for the plants and the bacteria. The bacteria
activity in the rhizosphere is 10-100 times more intensive than in soil without
vegetation. Bacteria profi t from their existence on and near the roots in many
