122
tivated), soil resistance (influenced by the frequency of soil cultivation apart from natural
conditions).
From the middle of the twentieth century soil
scientists tried to determine soil loss caused by
erosion in agricultural areas using exact methods.
Based on vast data of enormous outdoor experiments soil scientists in the USA created the
Universal Soil Loss Equation (Wischmeier et al.
1958; Wischmeier and Smith 1962, 1978) that
has been modified several times and is widely
used among experts. The basic equation is the
following
A R K L S C P
= ∗ ∗ ∗ ∗ ∗
where A = annual mean soil loss (t/ha/year),
R = erosion potential of precipitation (t/ha/year),
K = erodibility factor of soil (depending on
humus content, structure, mechanical composition), L, S = factor representing the erosion effect
of the length and steepness of slope (compared to
a parcel with a slope of 9%). C = factor of sowing
structure and the treatment of plant remnants
(compared to black fallow, i.e. vegetation free
land), P = factor of applied soil protection procedures and cultivation methods (compared to
slopeward cultivation). K, L, S, C and P are
dimensionless values.
Universal soil loss equation was developed by
various pedological research groups adjusting the
factors to geographical conditions but the basic
correlation remained the same. For the area of
Europe the so-called European Soil Erosion
Model (EUROSEM) was formed on the basis of
the works of Morgan et al. (1998) and Folly et al.
(1999). These theoretical works made it possible
that erosion protection remain on exact bases.
The EUROSEM model was assessed by several
scientists and it was also tested in field conditions
(Rosenmund et al. 2005; Mati et al. 2006; Morgan
and Nearing 2011).
If both intensity and spatial dimensions of erosion are considered, greatest soil loss appears in
Chinese loess areas and areas of tropical monsoon with greatest precipitation (Himalaya
region, Bangladesh, South-East Asia, China).
Wind erosion and deflation causes harm, on
the one hand, by removing loose soil decreasing
the nutrient supply and the retaining capacity of
the roots. On the other hand, the sand cover
formed by depositing the transported soil also
reduces fertility. Wind erosion is greatest in dry
and semi-dry environments and on sandy soils. It
also appears on harder soils as well if too much
cultivation is too frequent and the structure of the
original soil is lost. Most severe deflation can be
detected in agricultural areas along the margin of
large deserts (Fig. 4.38, “too dry”). Sahel region
south of the Sahara became infamous in this
respect in the last decades.
Secondary salinisation (soils becoming too
salty due to anthropogenic effects) hits mostly
semi-dry areas; however, it develops under different conditions. This process occurs only where
the subsoil contains dissolvable salt and shallow
groundwater table increases due to frequent irrigation. Soil moisture transports salts near the surface via capillaries where they are precipitated
from the solution due to strong evaporation.
Rarely even the irrigation water contains salt
more than permitted that accumulates in the top
layer of soils.
Both erosion and secondary salinisation could
result in so significant fertility decrease that plant
cultivation has to be stopped. As a consequence
people have to cultivate other areas taken away
from nature. This is most intense in tropical areas
where the reason for clearing the natural vegetation is most often to obtain new agricultural lands
and the most frequent way is grazing. This
increases the CO 2 and CH 4 content of the atmosphere, reduces biodiversity and intensifies erosion of the new agricultural areas as the protective
effect of the dense tropical vegetation is reduced.
Since tropical soils are less resistant to erosion
than those in temperate climate, plant cultivation
has to be stopped in the newly cultivated lands as
well within 5–6 years of cultivation.
Utilisation of strongly acid soils (Fig. 4.38,
“acid sulphate”) is limited. Acid soils can occur
as a result of natural processes (leaching) but
acidity of soils could be intensified by human
activities as well. Acid atmospheric deposition
(Sect. 4.5.3) and acidification due to the frequent
application of fertilisers could also reduce the
fertility of soils.
4 Changes on Earth as a Result of Interaction Between the Society and Nature
tivated), soil resistance (influenced by the frequency of soil cultivation apart from natural
conditions).
From the middle of the twentieth century soil
scientists tried to determine soil loss caused by
erosion in agricultural areas using exact methods.
Based on vast data of enormous outdoor experiments soil scientists in the USA created the
Universal Soil Loss Equation (Wischmeier et al.
1958; Wischmeier and Smith 1962, 1978) that
has been modified several times and is widely
used among experts. The basic equation is the
following
A R K L S C P
= ∗ ∗ ∗ ∗ ∗
where A = annual mean soil loss (t/ha/year),
R = erosion potential of precipitation (t/ha/year),
K = erodibility factor of soil (depending on
humus content, structure, mechanical composition), L, S = factor representing the erosion effect
of the length and steepness of slope (compared to
a parcel with a slope of 9%). C = factor of sowing
structure and the treatment of plant remnants
(compared to black fallow, i.e. vegetation free
land), P = factor of applied soil protection procedures and cultivation methods (compared to
slopeward cultivation). K, L, S, C and P are
dimensionless values.
Universal soil loss equation was developed by
various pedological research groups adjusting the
factors to geographical conditions but the basic
correlation remained the same. For the area of
Europe the so-called European Soil Erosion
Model (EUROSEM) was formed on the basis of
the works of Morgan et al. (1998) and Folly et al.
(1999). These theoretical works made it possible
that erosion protection remain on exact bases.
The EUROSEM model was assessed by several
scientists and it was also tested in field conditions
(Rosenmund et al. 2005; Mati et al. 2006; Morgan
and Nearing 2011).
If both intensity and spatial dimensions of erosion are considered, greatest soil loss appears in
Chinese loess areas and areas of tropical monsoon with greatest precipitation (Himalaya
region, Bangladesh, South-East Asia, China).
Wind erosion and deflation causes harm, on
the one hand, by removing loose soil decreasing
the nutrient supply and the retaining capacity of
the roots. On the other hand, the sand cover
formed by depositing the transported soil also
reduces fertility. Wind erosion is greatest in dry
and semi-dry environments and on sandy soils. It
also appears on harder soils as well if too much
cultivation is too frequent and the structure of the
original soil is lost. Most severe deflation can be
detected in agricultural areas along the margin of
large deserts (Fig. 4.38, “too dry”). Sahel region
south of the Sahara became infamous in this
respect in the last decades.
Secondary salinisation (soils becoming too
salty due to anthropogenic effects) hits mostly
semi-dry areas; however, it develops under different conditions. This process occurs only where
the subsoil contains dissolvable salt and shallow
groundwater table increases due to frequent irrigation. Soil moisture transports salts near the surface via capillaries where they are precipitated
from the solution due to strong evaporation.
Rarely even the irrigation water contains salt
more than permitted that accumulates in the top
layer of soils.
Both erosion and secondary salinisation could
result in so significant fertility decrease that plant
cultivation has to be stopped. As a consequence
people have to cultivate other areas taken away
from nature. This is most intense in tropical areas
where the reason for clearing the natural vegetation is most often to obtain new agricultural lands
and the most frequent way is grazing. This
increases the CO 2 and CH 4 content of the atmosphere, reduces biodiversity and intensifies erosion of the new agricultural areas as the protective
effect of the dense tropical vegetation is reduced.
Since tropical soils are less resistant to erosion
than those in temperate climate, plant cultivation
has to be stopped in the newly cultivated lands as
well within 5–6 years of cultivation.
Utilisation of strongly acid soils (Fig. 4.38,
“acid sulphate”) is limited. Acid soils can occur
as a result of natural processes (leaching) but
acidity of soils could be intensified by human
activities as well. Acid atmospheric deposition
(Sect. 4.5.3) and acidification due to the frequent
application of fertilisers could also reduce the
fertility of soils.
4 Changes on Earth as a Result of Interaction Between the Society and Nature