World Geography 3202
Chapter 8 (pp.135-140)
THE NATURE OF RESOURCES
Soil Characteristics
There are several characteristics of soil that affect its
value for farming and growing vegetation.
1. Organic Content
–
Soil fertility is determined as a ratio of the organic
content (residues of plants and animals) versus the
content of ground bed rock.
2. Mineral content
–
varies with precipitation because heavy rains tend to
leech soils removing minerals from the root region of soil
(calcium, magnesium, potassium, nitrogen).
3. Soil Texture
– refers to the mixture of fine particles (sand), very
fine particles (silt) and extra fine particles
(clay). The best texture for agriculture is an even
mixture of each.
Soil Profile
There are fairly distinct layers within soil.
– Top Layer: Dark color & rich in humus. The thickness
and quality of the top humus layer is very important
for plant life.
– 2nd Layer: Mineral layer deposited from above
(calcium, magnesium, potassium, nitrogen)
– 3rd Layer: Weathered bed rock
– 4th Layer: Bed rock
A Soil Profile
Types of Soil
1. Podzol
– soils which predominate the boreal forest and
tend to be somewhat acidic
2. Chernozem
– soils which tend to be the best for
agriculture. They are found in grasslands which
are semi-arid resulting in less leeching and a
mineral rich soil.
3. Latosol
– soils which are very infertile due to the high
amount of leeching. They are found in tropical
rain forests with high amounts of rain which
result in leeched mineral-poor soil.
Environmental Factors & Soil
1. Temperature
– affects the development of humus. Too cold and
the decay of organic matter is slowed
considerably.
2. Precipitation
– affects the mineral content of soil.
– too much rain and minerals are “leeched” down
beyond the reach of plant roots. The process of
leeching is also called “eluviation”
Soil Texture
• Soil texture refers to the size of particles in the
soil.
– stones are approximately baseball-sized;
– gravel is small stones;
– sand is fine particles;
– silt is very fine particles;
– clay is extremely fine particles.
• Soil is predominantly composed of sand, silt
and clay. Its texture is determined by the
mixture of these three.
• The best agricultural soils are an even mixture
of all three!
• The best mixture of all three (sand, silt and
clay) is called Loam.
Consider…
• What makes the best soil?
a) 40% sand, 20% clay and 60% silt OR
b) 30% sand, 60% clay, or 10% silt
The answer is A! Remember loamy soil is the best!!
Threats to Soil
• Poor soil management: can lead to loss of fertile
soil. While the earth's surface is covered in soil
the amount of fertile soil valuable for agriculture
is limited and is dwindling yearly.
• Expanding deserts: grasslands are semi-arid
regions with extremely fertile soil. If proper soil
management is not practiced these are among
the most fragile places. Globally desertification
of grasslands adjacent to deserts has been a
problem.
• Erosion: agricultural lands on slopes/hills or
mountains are very susceptible to water erosion.
• Urban expansion: has also been a factor in the
loss of agricultural land. People have traditionally
settled in rich farmland and increasing
urbanization is covering up good farmland.
• Overgrazing, flooding and deforestation: have led
to the degradation of arable land.
• Read pp. 135-142 (Earth’s Soil Resource)