Economic costs of soil erosion
The following questions can be asked related to the economic effects of
soil erosion:
1.
How high is the
decrease in crop yield per cm loss of topsoil depth? Does, in fact,
soil
productivity decrease much further, once the original humus rich
A1-horizon of the natural soil profile is gone, such as is the case in
large parts of Europe with its centuries
old cultural landscapes (provided that sufficient rooting depth
remains)?
2. What is the extent of the offsite damage caused by soil erosion
around the
world? How widespread is it?
3. How high
are the economic costs of soil
erosion around the world today? Is there a trend
in economic costs visible over the past hundred years?
4. How much does it
cost farmers to
apply soil erosion control measures on their farms?
5. On
how many acres of cultivated land around the world soil erosion control
measures are practiced today, and has this led to a reduction of the
onsite and offsite effects and related economic costs of soil
erosion?
Quantitative data to answer these
questions are scarce.
A preliminary question is: How
well do we really know the rate of soil erosion? On the measurement of
soil erosion Lal
(2001) remarks:
The
measurement
of
soil
erosion
is
still
more
of
an
art
than
science,
and
a
wide
range
of
techniques
are
used
to
monitor
soil
erosion.
There
is
a
strong
need
to
standardize
methods
of
measurement
of
soil
erosion
rates
at
field,
hillside
and
watershed
scales.
Fourteen years later Garcia-Ruiz
et
al.
(2015) in their paper "A meta-analysis of soil
erosion rates across the world" still warn that the data obtained have
not been independent of the method used. See also the review paper on
"Natural and anthropogenic rates of soil erosion" by Nearing
et
al
(2017).
Contrary views on the importance
of soil erosion have been expressed by Pimentel (1995, 2006, 2013) and
Crosson (1995, 2000).
Trimble
and
Crosson
(2000):
Soil
erosion
in
the United States has been a matter of public concern since
the 1930s. Conditions were improved by the 1960s, although no one knew
just how much. Starting in the 1970s, however, several studies
concluded that erosion was high. Although a few studies have been
skeptical of these high rates, most have suggested that soil erosion is
an extremely serious environmental problem, if not a crisis.
Quantification of the problem has been elusive, and average annual U.S.
cropland soil erosion losses have been given as 2 billion, 4.0 billion,
4.5 billion, 4.8 billion, 5 billion, or 6.8 billion tons.
The remarkable feature of all this
discussion and attempted rectification is that it was based mostly on
models. Little physical, field-based evidence (other than anecdotal
statements) has been offered to verify the high estimates. It is
questionable whether there has ever been another perceived public
problem for which so much time, effort, and money were spent in light
of so little scientific evidence.
Pimentel and Burgess
(2013):
Since humans worldwide obtain more than 99.7% of their food (calories)
from the land and less than 0.3% from the oceans and aquatic
ecosystems, preserving cropland and maintaining soil fertility should
be of the highest importance to human welfare. Soil erosion is one of
the most serious threats facing world food production. Each
year about 10 million ha of cropland are lost due to soil erosion, thus
reducing the cropland available for world food production. The loss of
cropland is a serious problem because the World Health Organization and
the Food and Agricultural Organization report that two-thirds of the
world population is malnourished. Overall, soil is being lost from
agricultural areas 10 to 40 times faster than the rate of soil
formation imperiling humanity’s food security.
Regarding the first of the five
questions above Bakker
et
al.
(2005) write as follows:
Although
the
problem
has
received
much
attention
recently,
hardly
any
quantitative
information
on
the
effect
of
erosion
on
agricultural
productivity
exists.
The
quantitative
information
derived
at
the
plot
scale
is
scattered
and
incoherent,
and
no
quantitative
information
at
the
regional
or
national
level
(i.e.
the
level
relevant
for
food
production)
exists.
Inferences
made
from
the
synchronicity
of
soil
erosion
events
and
societal
changes
are
therefore
not
based
on
quantitative
assessments
of
the
impact
of
soil
erosion
on
agricultural
productivity,
nor
are
analogies
between
the
collapse
of
an-cient
societies
and
the
risks
facing
modern
society.
For
this
reason,
the
extent
to
which
soil
erosion
is
indeed
a
significant
threat
to
the
agricultural
productivity
of
modern societies is an important
subject for debate.
The research presented here reports of
statistical analysis of both
plot and regional scale with respect to the erosion-productivity
relationship. A meta-analysis of plot scale experiments shows that the
different methodologies used for the erosion-productivity assessments
bear part of the responsibility for the incoherence of the outcomes.At
the plot scale, the effect of soil
erosion on crop growth has been assessed in numerous experiments where
erosion was either simulated by artificial desurfacing, or where
productivity losses in strongly eroded areas were compared with losses
from less eroded areas. A systematic overestimation of the effects may
apply to the first category of experiments, which make up a large part
of the research results. Correcting for this overestimation reveals
that under intensive,
mechanized agriculture yield reductions at the
field scale are of the order of only 4% for each 0.1 m of soil loss.
Given the fact that the removal of 0.1 m of soil required either long
time-spans, or very high erosion rates, this number makes it highly
unlikely that erosion may pose a serious threat to food production in
modern societies within the coming centuries. An empirical
analysis of
the relationship between erosion and productivity for modern
agriculture at the regional scale, also shows no agreement with
previous assumptions concerning the importance of the impact of erosion
on agricultural productivity either. The results of this analysis
converge with the corrected plot-scale findings of approx-imately 4%
per 0.1 m of soil loss. (underscored
by
FK)
The most comprehensive study of the impact of soil erosion on crop
productivity is Den
Biggelaar
et
al.
(Parts
1
and
2,
2004).
They start by remarking:
Despite
millions
of
dollars
invested
in
erosion
research,
it
is
difficult
to
state
precisely
what
effect
the
loss
of
a
unit
of
soil
has
on
crop
yield
(Lal,
1987a).
This
is
due
in
part,
as
Perrens
and
Trustum
(1984)
and
Erenstein
(1999)
observed,
to
the
fact
that
there
is
no
direct,
clear-cut
relationship
between
erosion
and
productivity,
making
the
assessment
of
the
impact
of
erosion
on
productivity
difficult.
Productivity
decline
may
not
relate
directly
to
the
amount
of
soil
loss
(expressed
in
Mg
or
cm
ha
21
yr
21
),
but
may
be
a
result
of
erosion-induced
changes
in
the
physical,
chemical,
and
biological
qualities
of
soil
that
influence
production
(e.g.,
water
holding capacity, soil organic matter (SOM) and nutrient
contents, and bulk density). Moreover, soil is only one of the factors
affecting productivity, as crop yield is a function of many variables.
One
of the conclusions of
Part 1 (p. 36) is:
The
results
of
the
present
analysis
show
that
average
crop
yields
and
effects
of
past
erosion
on
yields
(measured
in
Mg
yield
decline
per
cm
of
erosion)
differ
greatly
by
crop,
continent
and
soil
order.
However,
aggregated
across
soils
on
the
continental
level,
differences
in
productivity
declines
per
Mg
of
soil
erosion
are
fairly
small.
The
absolute
yield
loss
ranged
between
-0.49
and
1.44
kg/ha/Mg
of
soil
erosion
for
grain
and
leguminous
crops,
and
0.69
and
127.0
kg/ha/Mg
for
root
crops.
However,
due
to
differences
in
mean
yields,
the
relative
yield
losses
per
Mg
of
soil
erosion
vary
more,
even
though
losses
were
generally
small
(<<
0.1%/Mg
of
soil
erosion).
The
exceptions
to this general rule were studies on potatoes
in North America, in which yields declined by 0.42%/Mg.
In Part 2 (pp. 91-92) Den Biggelaar et
al. conclude:
Three main conclusions can be drawn from
our analyses:
First, estimated annual losses at a global
scale for the crops and continents considered in our analyses are small
relative to the total agricultural production and value of the selected
crops. The losses are likely to be masked over the short term by market
fluctuations, weather, and other environmental perturbations,
diminishing incentives for farmers to adopt conservation practices.
Moreover, erosion’s impacts are cumulative and may cause more serious
losses if it continues unabated over a long period of time.
Second, our estimated global annual losses in
crop yields and production are at the lower end of the range of
previously published estimates of erosion-induced productivity losses
(Lal and Stewart. 1990; Janargin and Smith, 1993; Crosson, 1997; Lal,
1998;Young, 1999). Of more interest, especially for soil conservation
policy is the finding that losses vary widely between crops, soil
orders and regions, and in selected situations can be quite
substantial. In general, though, little is known about these losses for
many important crops in many developing countries.
Third, estimated losses in productivity
are
probably small in relation to offsite impacts (such as sedimentation).
These
findings
underscore
the
importance
of
continued
policy
measures
to
encourage
soil
conservation.
They
also
underscore
the
importance
of
improved
understanding
of
erosion
and
its
impacts
for
these
crops,
soils,
and
regions
where
its
impacts
are
most
severe
or
least
understood.
Finally,
more
precise
estimation
of
actual
losses
due
to
erosion
(as
opposed
to
the
potential
losses
estimated
here)
depends
on
improved
understanding
of
farmers’
optimal
response
in
the
face
of
changing
physical,
market,
and
policy
environments.
Inman
(2006,
p.
16) on the economics of soil erosion in England and Wales:
The
costs borne by society as a consequence of soil erosion are known as
externalities by economists because they are costs which are not taken
into account either by producers or consumers of agricultural goods and
services. When such externalities are not included in prices, they
distort the market by encouraging activities that are costly to society
even if individual (private) benefits are large.
In the agricultural sector, externalities are regarded as having five
characteristics or features: 1) their costs are often neglected; 2)
they often occur with a time lag; 3) they often damage groups whose
interests are not represented; 4) the identity of the producer of the
externality is not always known and; 5) they result in sub-optimal
economic and policy solutions. Whilst it is relatively straight forward
to identify generic externality categories, quantifying many of these
categories in monetary terms is extremely difficult. Firstly, it is
necessary to know the value of nature’s goods and services, and what
happens to these when they are impacted. Secondly, many externalities
are associated with non-market goods. For example, how do we value
soil-water chemical interactions which produce clean water.
The following Table (from Telles, 2011, p. 293) gives estimates of soil erosion costs in dollars per year. The onsite costs were estimated on the basis of the loss of soil, nutrients, organic matter, productivity and yield. Offsite costs were estimated in various ways. However, the main offsite effects are linked to sedimentation. Depending on the methods used to estimate on- and offsite soil erosion costs, the results can be extremely variable. The majority of studies estimate onsite costs, and these studies show an even wider fluctuation in the estimated figures. Moreover, in terms of the breakdown of total erosion costs, offsite costs are higher than onsite costs.
Soil
erosion costs in dollars/year, data assembled from literature by Telles, 2011.
The
following
figure
gives
an
impression
of
the
economic
costs
of
soil
erosion
today: