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Soil Erosion Threatens Food Production

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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.
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Agriculture 2013, 3, 443-463; doi:10.3390/agriculture3030443
agriculture
ISSN 2077-0472
www.mdpi.com/journal/agriculture
Article
Soil Erosion Threatens Food Production
David Pimentel * and Michael Burgess
College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853, USA;
E-Mail: mnb2@cornell.edu
* Author to whom correspondence should be addressed; E-Mail: dp18@cornell.edu;
Tel.: +1-607-255-2212; Fax: +1-607-255-0939.
Received: 14 June 2013; in revised form: 20 July 2013 / Accepted: 23 July 2013 /
Published: 8 August 2013
Abstract: 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.
Keywords: soil erosion; malnutrition; cropland; rangeland; pasture; soil organic
matter; assessment
1. Introduction
The loss of soil from land surfaces by erosion is widespread and reduces the productivity of all natural
ecosystems as well as agricultural, forest, and pasture ecosystems [13]. Concurrently with the growing
human population, soil erosion, water availability, climate change due to fossil fuel consumption,
eutrophication of inland and coastal marine bodies of water, and loss of biodiversity rank as the prime
environmental problems throughout the world.
Currently nearly 66% of the world population is malnourished [4,5], the largest number of
malnourished people ever (malnutrition: faulty nutrition due to inadequate or unbalanced intake of
OPEN ACCESS
Agriculture 2013, 3 444
nutrients or their impaired assimilation or utilization) [6]. With the world population now over seven
billion and expected to reach 9.3 billion by 2050, more food will be needed [7]. Consider at present that
more than 99.7% of human food (calories) comes from the land [8], while less than 0.3% comes from the
marine and aquatic ecosystems. Maintaining and augmenting the world food-supply basically depends
on the productivity and quality of all agricultural soils.
Human induced soil erosion and associated damage to all agricultural land over many years have
resulted in the loss of valuable agricultural land due to abandonment and reduced productivity of the
remaining land which is partly made up for by the addition of nitrogen and phosphate fertilizers [2,911].
This loss of cropland to the effects of soil erosion often results in the creation of new cropland out of
forestland and pastureland and the need to enrich these new croplands with inputs of nitrogen and
phosphate fertilizers [12]. In addition, soil erosion reduces the valuable diversity of plants, animals, and
soil microorganisms.
In this paper, the diverse factors that cause soil erosion are assessed. The extent of damage associated
with soil erosion is analyzed, with emphasis on the impact these causative factors may have on future
human food security as well as on the natural environment.
2. Causes of Erosion
Erosion occurs when soil is left exposed to rain drop or wind energy. The raindrops hitting a hectare
of land in the New York State region of the United States provide the energy equivalent of 60,000 kcal
(250 × 10
6
joules) per year with about 1000 mm of rainfall [13]. This 60,000 kcal roughly equals the
energy in eight liters of gasoline. The raindrops hitting soil loosen the soil particles and with even a 2%
slope start the movement of the soil downhill. Sheet erosion is the dominant type of erosion [3,14]. The
impact of soil erosion is intensified on all sloping land, where with each degree of slope more of the
surface soil is carried away as the water moves downhill into valleys and streams.
Wind energy also has great power to dislodge surface soil particles and transport them long distances.
A dramatic example of this was the wind erosion in Kansas during the winter of 19951996 when it was
relatively dry and windy. At this time approximately 65 t/ha of soil was eroded from this valuable
cropland (Figure 1). Wind energy is sufficiently strong to propel soil particles thousands of kilometers.
This is illustrated in the photograph by NASA (Figure 2) which shows a cloud of sand being blown from
Africa to South and North America.
Figure 1. About 50 mm of soil blown from cropland in Kansas during the winter of
19951996 (E.L Skidmore, USDA, Manhattan, KS. photo spring of 1996).
Agriculture 2013, 3 445
Figure 2. Cloud of sand from Africa being blown across the Atlantic Ocean [15].
Agriculture 2013, 3 446
2.1. Soil Structure
Soil structure influences the ease with which soil can be eroded. Soils with a medium to fine texture,
a low level of organic matter content, and weak structural development are most easily eroded [16].
Typically these soils have low water infiltration rates and therefore are subject to high rates of water
erosion and are easily displaced by wind energy.
2.2. The Role of Vegetative Cover
Land areas covered by plant biomass, living or dead, are more resistant to wind and water soil erosion
and experience relatively little erosion because rain drop and wind energy are dissipated by the biomass
layer and the topsoil is held together by the biomass [17]. For example, in Utah and Montana, as the
amount of ground cover decreased from 100% to less than 1%, erosion rates increased approximately
200-fold [18]. In forested areas, a minimum of 60% forest cover is necessary to prevent serious soil
erosion and landslides [1921]. The extensive removal of forests for cropland and pasture is followed by
intensive soil erosion.
Loss of vegetative soil cover is especially widespread in developing countries where populations are
large and growing, and agricultural practices are often inadequate to protect topsoils. In addition,
cooking and heating in these countries frequently depend on the use of crop residues for fuel. For
example, in the 1990s about 60% of crop residues in China and 90% in Bangladesh routinely were
removed from the land and burned as fuel [22]. More recent estimates of the amount of crop residues in
Bangladesh that could be harvested for biomass energy conversion without negatively impacting future
crop yields amount to 50% of all rice crop residues and 80% of non-rice crop residues [23]. More
recently crop residues in China are being used less as a domestic fuel source [24] due to the increased
availability of fossil fuels. However China has plans to burn about half of the 600 billion tons of straw
(from grains) crop residues produced annually to generate electricity [25]. In areas where fuelwood and
other biomass are scarce, even the roots of grasses and shrubs are collected and burned [26,27]. All these
practices leave the soil barren and fully exposed to rain and wind erosion forces.
2.3. Land Topography
The topography of a given landscape, its rainfall and/or wind exposure all combine to influence the
land’s susceptibility to soil erosion. In the Philippines, where more than 58% of the land has a slope
greater than 11%, and in Jamaica where 52% of the land has a slope greater than 20%, soil erosion rates
as high as 400 t/ha/year have been reported [1]. Erosion rates are high especially on marginal and steep
lands which have been converted from forests to crops [1]. In addition under arid conditions with
relatively strong winds soil erosion rates as high as 5600 t/ha/year have been reported in an arid region in
India [28]. Even in a developed country with abundant farmland such as the United States where there is
less need to exploit croplands with steeper slopes, erosion losses as of 2007 average 13 tons/ha/year [29].
In a developed region such as Europe, the measured rates of erosion range between 3 and 40 tons/ha/year
with “losses due to individual storms of from 2040 tons/ha, that may happen every two or three years,
are measured regularly in Europe, with losses of more than 100 tons/ha in extreme events [30,31].
Agriculture 2013, 3 447
2.4. Other Soil Disturbances
Although world agriculture accounts for about three-quarters of the soil erosion worldwide, erosion
occurs whenever humans remove the vegetative cover [1,32]. The construction of roads, parking lots,
and buildings are examples of this problem. Although the rate of soil erosion from construction sites may
be exceedingly high, the erosion occurs for a relatively brief period. Once the land surface is seeded to
grass or covered with other vegetation, the erosion declines [3335].
Natural ecosystems also suffer erosion losses. This is especially evident along stream banks, where
erosion occurs naturally due to the powerful action of the adjacent moving water. Increased soil losses
occur on steep surfaces (30% or more) when a stream cuts through adjacent land. Even on relatively flat
land with only a 2% slope, stream banks are eroded during heavy rains and flooding.
3. Assessing Soil Erosion
Although soil erosion has been taking place very slowly in natural ecosystems throughout geologic
time, its cumulative impacts on soil quality over billions of years have been significant. Worldwide,
erosion rates range from a low of 0.001 t/ha/year on relatively flat land with grass or forest cover, to rates
ranging from 1 to 5 t/ha/year in mountainous regions with natural vegetation [36]. Yet even soil erosion
with low rates sustained over billions of years can result in the displacement of enormous quantities of
soil. In addition, eroded soil frequently accumulates in valleys forming alluvial plains. The large deltas
of the world, such as those of the Nile, Ganges and Mississippi Rivers are the result of millennia
of erosion [37].
Worldwide it is estimated that approximately 75 billion tons of fertile soil are lost from world
agricultural systems each year [38,39]. An estimate of the total amount of soil eroded by water from the
world’s arable land per year for land quality classes I through VI is 67 billion tons [40]. In the 1990s, soil
scientists Lal and Stewart [1] and Wen [41] report that 6.6 billion tons of soil per year are lost in India
and 5.5 billion tons are lost annually in China. According to a study conducted by the Central Soil Water
Conservation Research and Training Institute in Dehradun, India reported in 2010 that the average rate
of soil loss due to erosion in India is 16.4 tons per hectare annually with an annual total loss of 5.334
billion tons [42]. A three-year study conducted by researchers associated with the Chinese Ministry of
Water Resources, the Chinese Academy of Sciences and the Chinese Academy of Engineering reported
in 2009 that all of China’s 646 counties suffer from significant soil and water losses, equivalent to a
combined area of 3.75 million km
2
[43]. A two-year study further reports that if the current rate of soil
loss in China continues over the next 50 years, food production will decrease by 40% [44]. Considering
these two countries together occupy only 13% of the world’s total land area and have agricultural
practices that have sustained agriculture for thousands of years, the estimated 75 billion tons of soil lost
each year worldwide is conservative. The amount of soil lost from the United States cropland due to
water and wind has decreased from 3.06 billion tons in 1982 to 1.725 billion tons in 2007 [29].
Agriculture 2013, 3 448
3.1. Loss of Productivity in Managed Ecosystems
Approximately 50% of the earth’s land area is devoted to agriculture: About one-third is planted to
crops and two-thirds is grazing land [45]. Forests occupy about 20% of the world’s land area [46]. Of
these three areas, cropland is most susceptible to erosion because of the frequent cultivation of soils and
that vegetation is often removed before the crops are planted which exposes the soil to wind and rainfall
energy. In addition, cropland is often left without vegetative cover between plantings which intensifies
erosion on agricultural lands, erosion rates that are estimated to be 75 times greater than erosion in
natural forest areas [38].
3.2. Worldwide Cropland
Currently, about 80% of the world’s agricultural land suffers moderate to severe erosion, while 10%
experiences slight erosion [47,48]. Worldwide, erosion on cropland averages about 30 t/ha/year and
ranges from 0.5 to 400 t/ha/year [2]. As a result of soil erosion, during the last 40 years about 30% of the
world’s cropland has become unproductive and much of that has been abandoned for growing
crops [49,50].
The nearly 1.5 billion ha of world cropland now under cultivation for crop production are almost
equal in area to the amount of cropland (2 billion ha) that has been abandoned by humans since farming
began [51,52] (D. Pimentel, Personal Communication, 19 July 2013). Such abandoned land, once
biologically and economically productive, now only produces little biomass but also has lost
considerable diversity of the plants, animals, and microbes it once supported [11,52]. Each year an
estimated 10 million ha of cropland worldwide are abandoned due to lack of productivity caused by soil
erosion [53]. Worldwide, soil erosion losses are highest in agro-ecosystems of Asia, Africa, and South
America, averaging 30 to 40 tons/ha/year [11]. In developing countries, soil erosion is particularly
severe on small farms that are often located on marginal lands where the soil quality is poor and the
topography is frequently steep. In addition, poor farmers tend to raise row crops such as corn and beans;
row crops are highly susceptible to erosion because the crop vegetation does not cover the entire tilled soil
surface [54]. For example, in the Sierra Region of Ecuador, about 60% of the cropland was abandoned
because erosion and inappropriate agricultural practices left the land devastated by water and wind
erosion [55]. Similar problems are evident in the Amazonian region of South America, especially where
vast forested areas have been cleared to provide land for sugarcane and other crops, plus livestock
production. Past soil erosion for the African continent as a whole has caused an average annual crop
yield decline of 8.2% and 6.2% for sub-Saharan Africa [56] and that if higher soil erosion rates
continue unabated, average annual crop yield declines of 16.5% and 14.5% for sub-Saharan Africa may
be possible.
3.3. U.S. Cropland
The lowest average erosion rates on cropland occur in the United States and Europe ranging from
10 to 15 t/ha/year [57]; erosion rates in the United States have dropped from an average 16.4 t/ha/year in
1982 to 10.8 t/ha/year in 2007 [29]. However, even these relatively low rates of erosion greatly exceed
the average rate of natural soil formation from the parent soil material; under agricultural conditions the
Agriculture 2013, 3 449
soil formation rate ranges from 0.5 to 1 t/ha/year [2,3,9,58]. This means that most U.S. cropland is losing
soil faster than soil formation can replace it. Soil erosion is severe in some of the most productive
agricultural ecosystems in the United States. For example, one-half the fertile topsoil of Iowa has been
lost by erosion during the last 150 years of farming because of erosion [59]. These high rates of erosion
in 1982, about 16.6 t/ha/year, have been reduced but remain high at 11.5 t/ha/year as of 2007 in Iowa and
surrounding areas because of the rolling topography and the mostly corn and soybean production, row
crops where the soil surface between rows is left exposed to wind and rain [29,60,61]. Similarly, 40% of
the rich soil of the Palouse region in the northwestern U.S. has been lost during more than 100 years of
cultivation [62]. In both of these regions, intensive agriculture is employed and mono-cultural plantings
are common. In addition, most of the fields are left without a cover crop in the late fall and winter leaving
the soil exposed to further erosion. Yearly many valuable hectares of cropland are abandoned after they
have become unproductive due to wind and water erosion [63].
3.4. Pasture and Rangeland
In contrast to the average soil loss of 10.8 t/ha/year from U.S. cropland, pastures lose soil at about
6 t/ha/year [29,64]. However, erosion rates on pastures intensify whenever overgrazing occurs. Even in
the United States, about 75% of non-Federal lands require conservation treatments to reduce grazing
pressure [65]. More than half of the rangelands, including those on non-Federal and Federal lands, are
now overgrazed and have become subject to high erosion rates [66,67].
Although erosion rates on U.S. cropland have decreased during the past three decades, erosion rates
on rangelands and pastures remain high (6 t/ha/year) [64]. High erosion rates are typical on most of the
world’s pastures and rangelands [50]. In many developing countries, heavy grazing by cattle, sheep, and
goats has removed most of the vegetative cover, exposing the soil to severe erosion. In Africa, about
80% of the pasture and rangeland is seriously eroded and degraded [68]. The prime causes for exposed
soil are overgrazing and the removal of crop residues for cooking fuel but even by the 1990s researchers
realized that these causes are so intertwined with the effects of rainfall variability and the occurrence
of drought on the vegetation that it can be difficult to determine how much erosion is due to human
activity [69]. Rangeland degradation and resultant soil erosion often occurs in sub-Saharan Africa but
according to some researchers only under special circumstances such as when animals are concentrated,
due to a restriction of the animals’ movements, will a specific area of rangeland be overgrazed rather
than the overall rangeland [70].
3.5. Forest Land
In stable forest ecosystems, where soil is protected by vegetation, erosion rates are very low, ranging
from only 0.004 to 0.05 t/ha/year [47,71]. Tree leaves and branches not only intercept and diminish
raindrop and wind energy, but leaves and branches also cover the soil under the trees to further protect
the soil. However, the situation changes dramatically when forests are cleared for cropland or pastures
are developed for livestock production and the soil is exposed to rain and wind energy [55,72].
Agriculture 2013, 3 450
4. Effects of Soil Erosion on Terrestrial Ecosystems
Soil erosion reduces the general productivity of terrestrial ecosystems [73,74]. In the order of
importance, soil erosion increases water runoff thereby decreasing water infiltration and the
water-storage capacity of the soil [3]. In addition, during the erosion process organic matter and essential
plant nutrients are removed from the soil and soil depth is reduced. These changes not only inhibit
vegetative growth but reduce the presence of valuable biota and the overall biodiversity of the
soil [3,74]. These factors interact, making it almost impossible to separate the specific impacts of one
factor from another. For example, the loss of soil organic matter increases water runoff which reduces
the soil’s water-storage capacity, which diminishes nutrient levels in the soil and also reduces the natural
biota biomass and the biodiversity of soil ecosystems [7375].
4.1. Water Availability
Water is a prime limiting factor for productivity in all terrestrial ecosystems because all vegetation
requires enormous quantities of water for growth and for the production of fruit [76]. For example, 1 ha
of corn will transpire about seven million liters of water during the growing season of about
three months [77] and lose an additional two million liters of water by evaporation from the soil [76].
During soil erosion by rainfall, water runoff significantly increases with less water entering the soil and
less water available to support the growing vegetation.
4.2. Nutrient Losses
Eroded soil carries away vital plant nutrients such as nitrogen, phosphorus, potassium, and calcium.
Typically, the eroded soil contains about three times more nutrients per unit weight than are left in the
remaining soil [78]. A ton of fertile topsoil averages 1 to 6 kg of nitrogen, 1 to 3 kg of phosphorus, and
2 to 30 kg of potassium, whereas the topsoil on the eroded land has an average nitrogen content of only
0.1 to 0.5 kg per ton [79,80]. To offset the nutrient losses inflicted by crop production, large quantities of
fertilizers are often applied. Troeh et al. [3] estimate that lost soil nutrients cost U.S. agriculture several
billion dollars annually. If the soil base is relatively deep, about 300 mm, and if only from 10 to 20 tons
of soil is lost per hectare per year, the lost nutrients can be replaced with the application of commercial
fertilizers and/or livestock manure. However, the replacement strategy is expensive for the farmer and
nation and usually poor farmers cannot afford fertilizer. Not only are the fertilizer inputs fossil-energy
dependent, these chemicals can harm human health and pollute the soil, water and air [64,81].
4.3. Soil Organic Matter
Fertile soils typically contain 100 tons of organic matter per hectare (4% to 5% of total topsoil
weight) [17,58]. About 95% of the soil nitrogen and 25 to 50% of the phosphorus is contained in the soil
organic matter [82]. Because most soil organic matter is found close to the soil surface as decaying
leaves and stems, erosion significantly reduces the soil organic matter. Both wind and water erosion
selectively remove the fine organic particles in the soil leaving behind larger soil particles and stones.
Several studies have demonstrated that the soil removed by either water or wind erosion is 1.3 to 5 times
richer in organic matter than the soil left behind [1]. For example, the reduction of soil organic matter
Agriculture 2013, 3 451
from 0.9% to 1.4% (assuming a soil organic content of 4 to 5%) lowered the crop yield potential for grain
by 50% [58,83].
Soil organic matter is a valuable resource because it facilitates the formation of soil aggregates and
thereby increases soil porosity. The improved soil structure in turn facilitates water infiltration and
ultimately the overall productivity of the soil [80]. In addition, organic matter aids cation exchange,
enhances plant root growth, and stimulates the increase of important soil microbes [75,82,84].
Once the organic matter layer is depleted, the productivity of the ecosystem, as measured by plant
biomass, declines both because of the degraded soil structure and the depletion of nutrients that were
contained in the organic matter. In addition to low yields, the total biomass of the biota and overall
biodiversity of these ecosystems is substantially reduced [85,86].
4.4. Soil Depth
Growing plants require soils of adequate depth in which to extend their roots. Various soil biota, like
earthworms, also require a suitable soil depth [2,84]. Thus, when erosion substantially reduces soil depth
of from 30 cm for deep soils to even less than 1 cm for thin soils, plant root space can be minimized, and
the plants could be stunted.
5. Biomass, Soil Biota and Biodiversity
The biological diversity existing in any ecosystem is directly related to the amount of living and
non-living organic matter present [52,8487]. As mentioned, erosion, by diminishing soil organic matter,
reduces the overall soil biomass and biological activity. Ultimately, this has a profound effect on the
diversity of plants, animals, and microbes present in the soil ecosystem. Numerous positive associations
have been established between biomass abundance and species diversity [8891]. Vegetation is the main
component of ecosystem biomass and provides the vital resources required both by animals and
microbes for their survival. This is illustrated in Table 1 [92]. Along with plants and animals, microbes
are a vital component of the soil and constitute a large percentage of the soil biomass. One cubic meter of
soil may support up to 200,000 arthropods, 10,000 earthworms, plus billions of microbes [74,93,94]. A
hectare of productive soil may have a biomass of invertebrates and microbes weighing up to 10,000
kg/ha (Table 1). In addition, soil bacteria and fungi add 4000 to 6000 species and in this way contribute
significantly to biodiversity especially in moist, organic soils [52,74].
Erosion rates that are 10 to 20 times above the sustainability rate or soil formation rates of
0.51 t/ha/year reduce the diversity and abundance of soil organisms [74,95]. In contrast, agricultural
practices that control erosion and maintain adequate soil organic matter favor the proliferation of soil
biota [74,96,97]. The application of organic matter or manure also enhances the biodiversity in the
soil [74,98]. Species diversity of macrofauna (mostly arthropods) increased 16% when organic matter or
manure was added to experimental wheat plots in Russia [99]. Similarly, species diversity of macrofauna
(mostly arthropods) more than doubled when organic manure was added to grassland plots in
Japan [100], and increased 10-fold in Hungarian farm land [101].
Agriculture 2013, 3 452
Table 1. Biomass of various organisms per hectare in a temperate region pasture [92].
Organism
Biomass (kg fresh weight)
Plants
20,000
Fungi
4,000
Bacteria
3,000
Arthropods
1,000
Annelids
1,320
Protozoa
380
Algae
200
Nematodes
120
Mammals
1.2
Birds
0.3
Field experiments using collards confirm the relationship between biomass and biodiversity in
which arthropods species diversity rose 4-fold in experimental plots with the highest collard biomass
compared with that found in control collard plots [102]. Depending on the soil type, ecological
characteristics of the area, and land use practices, one hectare of productive soil can contain as many as
21,000 species [74]. In a study of bird populations, a strong correlation between plant biomass
productivity and bird species diversity was reported when a 100-fold increase in plant biomass yielded a
10-fold increase in bird species diversity [87].
Soil erosion has indirect effects on ecosystems that may be nearly as damaging as the direct effects in
reducing plant biomass productivity. Tilman and Downing [103] found that the stability and biodiversity
of grasslands were significantly reduced when the number of plant species decreased; as plant species
richness decreased from 25 species to five or less, the grassland became less resistant to drought. The
overall result was that the grassland was more susceptible to drought conditions and required more time
to recover its productivity than when a greater abundance of plant species was present.
Sometimes soil erosion causes the loss of a keystone species, and that keystone species absence may
have a cascading effect on the survival of a wide array of other species within the ecosystem. Species
that act as keystone species include the dominant plant type, like oaks, that maintain the biomass
productivity and integrity of the ecosystem; predators and parasites that control the feeding pressure of
some organisms on major plants; pollinators of various plants in the ecosystem; seed dispersers; as well
as the plants and animals that provide habitats required by other essential species like biological nitrogen
fixers [72,74]. Thus, in diverse ways, the normal activities within an ecosystem may be interrupted when
the populations of keystone species are significantly altered. The damages inflicted can be severe in
agro-ecosystems when, for instance, the numbers of pollinators are drastically reduced or even
eliminated and there is little or no reproduction in the plants affected [2,74].
Soil biota perform many beneficial activities that improve soil quality and ultimately its
productivity [74,96,104,105]. For example, soil biota recycle basic nutrients required by plants for
their growth [74]. In addition, the tunneling and burrowing activities of earthworms and other soil
biota enhance soil productivity by increasing water infiltration [104]. Earthworms, for instance, may
construct up to 220 tunnel channels per square meter in old bush fallow areas in Nigeria while cultivated
areas had only 34 channels per square meter and the channel diameters in the cultivated areas were
narrower [106]. These channel openings enable the water to infiltrate rapidly into the soil. Other soil
Agriculture 2013, 3 453
biota contribute to soil formation and productivity by mixing the soil components, enhancing aggregate
stability, and preventing soil crusting. This churning and mixing of the upper soil redistributes nutrients,
aerates the soil, exposes soil to the weather for soil formation, and increases water infiltration rates, thus
making soil conditions favorable for increased soil formation and plant productivity. Earthworms bring
from 10 to 500 t/ha/year of soil from underground to the soil surface [107,108], while some insects, like
ants, may bring 34 t/ha/year of soil to the surface [109,110]. Snails are reported to help the formation of
1000 kg/ha of soil per year [111].
6. Sediments and Wind Blown Soil Particles
Beyond the damage to rain fed agricultural and forestry ecosystems, the effects of erosion reach far
into surrounding environments [112]. For instance, large amounts of eroded soil are deposited into
streams, rivers, lakes, and other ecosystems. The USDA [60] reports that 60% of water-eroded soil ends
up in streams. In China, approximately 12 billion tons/year of soil was transported down the Yellow
River into the Yellow Sea from 19501970 but since the late 1980s the sediment load has decreased due
to better soil conservation practices on the Loess Plateau, and the greater use of Yellow River water for
irrigation, human consumption and industrial uses [113115]. The most costly off-site damages occur
when soil particles enter lake or river systems [116,117]. Of the 75 billion tons of soil lost worldwide,
approximately two-thirds become deposited in lakes and rivers [60,118]. In some areas, heavy
sedimentation leads to river and lake flooding [38,39]. Some of the flooding that occurred in the
midwestern United States during the summer of 1993 was caused by increased sediment deposition in
the Mississippi and Missouri Rivers. These deposits raised the level of the waterways, making them
more prone to overflowing and flooding [119]. Sediments disrupt and harm aquatic life by contaminating
the water with soil particles, fertilizers, and pesticides [120]. Siltation of reservoirs and dams reduces
water storage, increases the maintenance cost of the dams, and shortens the life of the reservoirs [2].
Wind-eroded soil also causes off-site damage because soil particles propelled by strong winds act as
abrasives and air pollutants [121,122]. Soil particles sand-blast U.S. automobiles and buildings and
caused an estimated $8 billion in damage each year during the 1980s [2,123]. A prime example of the
environmental impact of wind erosion occurs in the U.S., where wind erosion rates average 13 t/ha/year
on cropland and sometimes reach 65 t/ha/year [124]. Yearly off-site erosion costs in New Mexico in
1984, including health and property damage, are estimated to be nearly $500 million [123]. The
estimated total damage from wind erosion in the U.S. was estimated to cost nearly $10 billion each year
in the 1990s [2].
The long range transport of dust by wind has implications for health worldwide. Griffin et al. [125]
report that about 20 human infectious disease organisms, like anthrax and tuberculosis, are easily carried
in the soil particles transported by the wind. Inhaled dust can also cause problems such as irritation of the
respiratory passages and diseases such as lung cancer and dust can carry harmful materials such as
organic chemicals, heavy metals, and radioactive materials into the lungs [81].
Soil erosion contributes to global warming because CO
2
is added to the atmosphere when enormous
amounts of biomass in the soil are exposed to the air and oxidized [86,126129]. One hectare of soil may
contain about 100 tons of organic matter or biomass; if eroded and oxidized, this erosion would
Agriculture 2013, 3 454
contribute about 45 tons of carbon to the atmosphere. A feedback mechanism exists wherein increased
global warming intensifies rainfall which, in turn, increases erosion and continues the cycle [128].
7. Conservation Technologies and Research
Estimates are that agricultural land degradation alone can be expected to depress world food
production as much as 30% during the next 50 years [49]. This forecast emphasizes the need to
implement known soil conservation techniques. These soil conservation techniques include biomass
mulches, crop rotations, no-till, ridge-till, added grass strips, shelterbelts, contour row-crop planting, and
various combinations of these. Basically all of these techniques require keeping the land protected from
wind and rainfall energy by using some form of biomass cover on the land which means either leaving
most of the crop residues on the cropland or planting cover vegetation on a harvested cropland [2,3,11].
In the U.S. during the past decade, soil erosion rates on croplands have been reduced over 25% using
various soil conservation technologies [57,130]. Yet, even with the decline in erosion, soil is still being
lost at a rate 10 to 15 times above sustainability [64]. However, soil erosion rates on pasture and rangelands
have not declined during the past 20 to 30 years and still remain six times above sustainability [64].
8. Conclusion: Productive Soils and Food Security
Soil erosion is a disastrous environmental problem throughout the world. Erosion is a slow insidious
problem that is continuous. Indeed, 1 mm of soil, easily lost in one rain or wind storm, is so minute that
its loss goes unnoticed by the farmer and others. Yet this loss of soil over a hectare of cropland amounts
to about 15 t/ha. Replenishing this amount of soil under agricultural conditions requires approximately
20 years, meanwhile the lost soil is not available to support crops. Along with the loss of soil is the loss
of water, nutrients, soil organic matter, and soil biota. The soil system is severely harmed when soil
erosion is allowed to occur.
Future food security is threatened where cropland degradation is allowed to occur because of
significantly reduced crop productivity. Shortages of cropland are already having negative impacts on
world food production [131,132]. For example, the Food and Agricultural Organization (FAO) of the
United Nations reports that the per capita grain production has been declining for more than two
decades, based on the availability of grains (Figure 3). Note, cereal grains make up more than 80% of the
world’s food. Although grain yields per hectare in both developed and developing nations are still
increasing, these increases are slowing.
Worldwide, soil erosion continues unabated while the human population continues to increase rapidly
and 66% of the world population is now malnourished [4]. If soil conservation is ignored and population
control is ignored, more malnourished people and more deaths will occur.
Agriculture 2013, 3 455
Figure 3. Cereal Grain Production per capita in the world from 1961 to 2010 [58,133].
Acknowledgments
We wish to express our sincere gratitude to the Cornell Association of Professors Emeriti for the
partial support of our research through the Albert Podell Grant Program.
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... These pores hold air and water, which are essential for root respiration and microbial activity. Soils with high porosity allow for better water infiltration and reduce the risk of waterlogging or drought stress (Pimentel & Burgess, 2013). ...
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Chapter
Land degradation from soil erosion has been considered by many to be a problem of significant proportion, affecting some 30–50% of the earth's land surface. At the time of the first publication of this book in 1993, estimates indicated that 10–15 million hectares of land were being lost each year through erosion and salinisation from irrigation and that at such a rate of loss, topsoil reserves on most sloping lands would be depleted within two hundred years. Since humankind's dependency on the land for food is almost total, soil erosion represents a real threat to the security of our food supply. The need for the immediate conservation of the world's soil resources is therefore clear. As part of the response to this need, the International Union for the Conservation of Nature's Commission on Ecology convened a special working group to consider the problem of world soil erosion and to propose practical solutions for soil conservation. This important book presents the outcome of their work.
Book
This book provides an authoritative review of the resources of soils, water, climate, forests and pastures on which agriculture depends. It assesses the interactions between land resources and wider aspects of development, including population and poverty. Unless action is taken, the developing world will face recurrent problems of food security and conflict. The book gives some forcefully-expressed criticisms of current methods of assessing land degradation and placing an economic value on land. It should be read by all involved in rural development, including scientists, economists, geographers, sociologists, planners, and students of development studies. It provides a summary and perspective of the field of land resources, and suggests improvements needed to conserve resources for future generations. The hardback edition of the book received excellent reviews.
Chapter
Land degradation from soil erosion has been considered by many to be a problem of significant proportion, affecting some 30–50% of the earth's land surface. At the time of the first publication of this book in 1993, estimates indicated that 10–15 million hectares of land were being lost each year through erosion and salinisation from irrigation and that at such a rate of loss, topsoil reserves on most sloping lands would be depleted within two hundred years. Since humankind's dependency on the land for food is almost total, soil erosion represents a real threat to the security of our food supply. The need for the immediate conservation of the world's soil resources is therefore clear. As part of the response to this need, the International Union for the Conservation of Nature's Commission on Ecology convened a special working group to consider the problem of world soil erosion and to propose practical solutions for soil conservation. This important book presents the outcome of their work.
Chapter
The human race now appears to be getting close to the limits of global food productive capacity based on present technologies. Substantial damage already has been done to the biological and physical systems that we depend on for food production. This damage is continuing and in some areas is accelerating. Because of its direct impact on global food production, injury and loss of arable land has become one of the most urgent problems facing humanity. Of these problems, this is perhaps the most neglected. Controlling these damaging activities and increasing food production must now receive priority and resources commensurate with their importance if humanity is to avoid harsh difficulties in the decades ahead.