Environmental Engineering Reference
In-Depth Information
The organic matter in soils greatly modifies the physical properties and can mitigate
the adverse properties of loose sands and heavy clays. It has colloidal properties, provides
nutrients such as nitrogen and sulphur, and provides energy for soil micro-organisms.
FURTHER READING
Brady, N. C., and Weil, R. R. (1999)
Nature and Properties of Soils
, twelfth edition, London:
Macmillan. The latest edition of a comprehensive and popular textbook. The examples are
mostly American.
Rowell, D. L. (1994)
Soil Science: methods and applications
, London: Longman. A detailed
discussion of soil physical and chemical properties. Many examples of practical work in the
field and the laboratory are given.
Wigley, T. M. L., and Schimel, D. S., eds (2000)
The Carbon Cycle
, New York: Cambridge
University Press. An important reference for up-to-date information on the certainties and
uncertainties of the global carbon cycle.
KEY POINTS
1
The important phy sical properties of soil are texture, structure, water-holding capacity,
permeability, infiltration capacity and aeration. These properties result from the
mineral part of the soil (sand, silt, clay) and the organic fraction (humus, raw organic
matter).
2
The colloidal fraction in soil consists of clay minerals and humic colloids. They have
net negative charges with the ability to hold exchangeable cations by adsorption. The
amount and nature of exchangeable cations govern many chemical properties, such as
base status and soil reaction.
3
The fertility of a soil reflects its physical, chemical and biological properties. The yield
of crops will reflect any adverse fertility factors affecting water, air, nutrients or
physical support. Any limitation on the soil's ability to provide these four essential
factors has serious consequences for soil fertility.
