96 Ecology and Applied Environmental Science
5.2.7.2 Transformation to Laterite
In the warm and humid tropical regions, the soil is subjected, besides
erosion, to the danger of its transformation to laterite. Laterites occur in
all tropical regions and are characterized by a high content of iron and
aluminum, a small quantity of silicon and an acid reaction. Many types of
rock can be transformed to laterite after they are decomposed under the
influence of continuous leaching out by pelting rains in combination with
the high temperatures, due to intense solar radiation. Water penetration
causes the removal of the more soluble elements, such as sodium, potassium, magnesium and silicon. Thus the concentration of the less soluble
elements, especially iron and aluminum, increases. Laterite is usually a few
meters deep. It may occur in non-tropical regions also, but in that case it is
a product of previous geologic periods.
etation. Tropical forests can also develop in infertile soil, where the extraordinary bloom of life is due to the quick and almost perfect recycling of
nutrient salts, thanks to the high temperature and the abundance of light
and water. When the primary tropical forest disappears by fire or clearing,
the soil suffers the consequences of intense leaching; as a result, its structure is altered and laterite is gradually formed, which renders the growth
of plants almost impossible. The tropical forest degradation process is very
fast, because the layer of dead organic matter (leaf coverage and humus),
that in northern forests can reach a depth of a few meters, does not exceed a
depth of a few centimetres since decomposition takes place almost immediately. Thus it is possible that large expanses of forests could be irrevocably
lost in a few years; moreover, those expanses become unsuitable for any
agricultural use and even for a potential reforestation effort.
5.2.7.3 Salination of Soil
Besides erosion, the cultivation of soils with friable structure can cause
irreparable chemical alteration, which renders them unsuitable for exploitation and obstructs even the recovery of the initial vegetation.
Soil salination is known since antiquity as a great scourge for agriculture. It comes from inadequate drainage of cultivations or from the
presence of a high level water table in combination with profound evapotranspiration favoured by draught and high temperature. The result is the
accumulation of salt on the top-soil and the formation of salty plaques.
In some cases, irrigation, by leaching out the soil, causes an irreversible
change of its structure, thus making the problem even more serious.
Calcium is removed and substituted by sodium that moves towards
the top-soil during the dry period. The formation of sodium carbonate
5.2.7.2 Transformation to Laterite
In the warm and humid tropical regions, the soil is subjected, besides
erosion, to the danger of its transformation to laterite. Laterites occur in
all tropical regions and are characterized by a high content of iron and
aluminum, a small quantity of silicon and an acid reaction. Many types of
rock can be transformed to laterite after they are decomposed under the
influence of continuous leaching out by pelting rains in combination with
the high temperatures, due to intense solar radiation. Water penetration
causes the removal of the more soluble elements, such as sodium, potassium, magnesium and silicon. Thus the concentration of the less soluble
elements, especially iron and aluminum, increases. Laterite is usually a few
meters deep. It may occur in non-tropical regions also, but in that case it is
a product of previous geologic periods.
etation. Tropical forests can also develop in infertile soil, where the extraordinary bloom of life is due to the quick and almost perfect recycling of
nutrient salts, thanks to the high temperature and the abundance of light
and water. When the primary tropical forest disappears by fire or clearing,
the soil suffers the consequences of intense leaching; as a result, its structure is altered and laterite is gradually formed, which renders the growth
of plants almost impossible. The tropical forest degradation process is very
fast, because the layer of dead organic matter (leaf coverage and humus),
that in northern forests can reach a depth of a few meters, does not exceed a
depth of a few centimetres since decomposition takes place almost immediately. Thus it is possible that large expanses of forests could be irrevocably
lost in a few years; moreover, those expanses become unsuitable for any
agricultural use and even for a potential reforestation effort.
5.2.7.3 Salination of Soil
Besides erosion, the cultivation of soils with friable structure can cause
irreparable chemical alteration, which renders them unsuitable for exploitation and obstructs even the recovery of the initial vegetation.
Soil salination is known since antiquity as a great scourge for agriculture. It comes from inadequate drainage of cultivations or from the
presence of a high level water table in combination with profound evapotranspiration favoured by draught and high temperature. The result is the
accumulation of salt on the top-soil and the formation of salty plaques.
In some cases, irrigation, by leaching out the soil, causes an irreversible
change of its structure, thus making the problem even more serious.
Calcium is removed and substituted by sodium that moves towards
the top-soil during the dry period. The formation of sodium carbonate