Geoscience Reference
In-Depth Information
KEY POINTS
1
The important physical properties of soil are texture, structure, bulk density, available-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 pH and base saturation.
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, according to Liebig's
'Law of the Minimum'.
4
Loss of soil fertility by overcropping and overgrazing is becoming more serious. Soil erosion is also a
serious problem, in both LEDCs and MEDCs. Its natural controls are climate, vegetation cover, slope
steepness and length, and the soil's properties of texture and structure. However, land management is
crucial. Human use of the Earth for arable cropping and animal grazing, coupled with increasing amounts
of deforestation, road construction and 'development' in all its aspects, has accelerated soil loss to
unacceptable levels in many land management systems. Alternative techniques of husbandry, in the form
of organic and biodynamical farming, have been suggested in order to achieve a more sustainable use of
our greatest resource - the soil.
FURTHER READING
Ashman, M. R. and Puri, G. (2002) Essential Soil Science, Oxford: Blackwell. A clearly written introduction to soil science
which explains essential concepts by the use of innovative, everyday analogies in the text and illustrations.
Brady, N. C. and Weil, R. R. (2004) Elements of the Nature and Properties of Soils, Upper Saddle River, NJ: Prentice Hall.
The latest version of this famous US textbook, which ran into thirteen editions! A very comprehensive and popular
treatment. Clear exposition and student-friendly, although most examples are American.
Fullen, M. A., and Catt, J. A. (2004)
Soil Management: problems and solutions, London: Hodder. A detailed yet accessible
treatment of the latest research on soil management issues, including climate change and human health.
Lampkin, N. (2002) Organic Farming, Ipswich: Old Pond. The organic farmer's bible!
WEB RESOURCES
http://www.cranfield.ac.uk/nsri A
s well as being involved in mapping soils (see
Chapter 18),
the National Soil Resources
Institute (NSRI), Cranfield University, has been active in many applied studies of soil use and sustainability, e.g. soil
acidification, soil carbon balances, soil reclamation.
http://www.defra.gov.uk/farm/organic/index.htm T
he website of the Department of Environment, Food and Rural Affairs
(DEFRA) which gives advice to organic farmers on matters of techniques, husbandry, economics, and subsidies.
http://macaulay.ac.uk A
s well as being involved in pedological studies (see
Chapter 18),
the Macaulay Land Use Research
Institute (MLURI), Aberdeen, actively researches, and produces policy documents on, the sustainable use of soils for
agriculture, forestry, wildlife conservation and recreation.
http://www.soilassociation.org T
he Soil Association is the foremost non-governmental organization (NGO) which researches
into, and promotes, organic farming in the United Kingdom. It inspects farms and awards its reputable kite mark.
