“A nation that destroys its soils destroys itself.”
- Franklin D. Roosevelt i
Healthy soils are essential for the production of crops
used to feed humans and livestock. In addition to providing a
stable base to support plant roots, soils store water and
nutrients required for plant growth.
Unfortunately, industrial agriculture practices continue
to damage and deplete this valuable natural resource. While
intensive plowing and monocrop agriculture systems have caused
nutrient depletion and wide-scale soil erosion, over-application
of fertilizers and pesticides have
contaminated our soils and polluted
our waterways.
Fortunately, many farmers are choosing to use sustainable
agricultural techniques such as conservation tillage, crop
rotation, and organic fertilization in order to protect our
valuable soil resources.
Soil Erosion
Erosion is the movement of soil by water, wind, or gravity.
Although this process occurs naturally throughout the world,
industrial farming practices have dramatically increased the
speed at which agricultural soils are eroded. Currently, the
average rate of soil erosion on U.S. cropland is 7 tons per acre
per year.iii
The rate of erosion is highest when soil is not covered
by a protective layer of plants or decaying organic matter.
Industrial farmland is particularly susceptible to erosion due
to intensive tillage (plowing), which eliminates protective
ground cover from the soil surface and destroys root systems
that help hold soil together.
Since soil formation is an extraordinarily slow process,
erosion poses a serious problem; soil erosion can quickly cause
fertile farmland to become unsuitable for agriculture. In
extreme cases, erosion can lead to desertification, a process
which causes arid soil to become barren and incapable of
sustaining plant growth for many years.
However, even low rates of soil erosion can severely
damage agricultural land; not only does erosion reduce the water
holding capacity of a given soil, it also strips away nutrients
and organic matter. In fact, soil removed by erosion contains
about 3 times more nutrients and 1.5 to 5 times more organic
matter than the soil that remains behind.v
The National Sustainable Agriculture Information Service
notes that erosion is the single greatest threat to soil
productivity.vi According to a 1995 study published
in Science, the loss of soil and water from U.S. cropland
decreases productivity by about $27 billion per year.vii
Pollution & Damage Caused
by Erosion
In addition to removing valuable soil from farmland, erosion
pollutes waterways with sediment. Runoff containing sediment
degrades aquatic ecosystems by reducing stream depth and
increasing turbidity (making water cloudier), causing the
population of fish and other aquatic organisms to decline.
According to the EPA, sediment is the most significant non-point
source (NPS) pollutant in the U.S.viii
Eroded sediment also affects humans by disrupting
drainage systems, increasing the cost of water treatment,
filling up reservoirs, and obstructing waterways. Furthermore,
wind erosion damages buildings and covers roads, railways, and
other structures with soil. The resulting damages and increased
maintenance costs amount to approximately $8 billion per year.ix
Erosion Control
Erosion can be significantly reduced through sustainable
agricultural practices. The most effective way to prevent
erosion is to protect soil from the direct impact of rain and
wind by keeping it covered with plants and/or decaying organic
matter.
While industrial farms lose tons of soil as a result of
intensive tillage (plowing), sustainable farmers have
successfully reduced erosion by adopting conservation tillage
techniques such as no-till, mulch-till, and ridge-till systems.
These systems minimize soil disturbance and leave 'crop residue'
(plant parts that remain after harvest) covering the soil.
No-till systems are most effective; in no-till fields, all plant
residue is left on the soil surface, and less than 10% of the
soil is disturbed during planting.x
In addition to reducing erosion, conservation tillage
enables soil to retain more moisture, reduces soil crusting (the
formation of a rigid crust atop soil), and allows organic
materials such as leaves and plant parts to accumulate over
time, helping to restore nutrients to the soil. This technique
also requires less labor, equipment, and fossil fuel.xi
According to the Conservation Technology Information Center
(CTIC), conservation tillage enables U.S. farmers to save 306
million gallons of fuel each year - this reduces annual
greenhouse gas emissions by over 1 billion pounds of carbon
dioxide!xii
Sustainable farmers also reduce erosion by creating
buffer strips within fields. For instance, wind erosion can be
prevented by planting strips of trees or vegetation at the edges
of fields. Farmers can also create buffer strips consisting of
grasses or shrubs alongside drainage ditches and streams in
order to help prevent water erosion.
Soil Nutrients and
Fertilizer
Plants need more than just sunlight and water! In order to grow,
plants require a variety of different nutrients (see sidebar).
In natural environments such as prairies and forests, plants
obtain most necessary nutrients from minerals found within the
soil. When these plants die, they fall to the ground, decompose,
and release nutrients back into the soil, making them available
for new plants. In this way, nutrients are "recycled" with each
generation of plants.
On farms, the nutrient cycle is somewhat different. Since
crops are continually harvested or eaten by grazing livestock,
there is no steady supply of decaying plant material to
replenish nutrient levels within the soil. Instead, nutrients
must be restored by adding fertilizers to the soil.
Traditionally, agricultural soils were fertilized using
livestock manure, which is rich in nutrients and organic matter.
Farmers also practiced crop rotation, regularly alternating the
types of crop grown in various fields and periodically allowing
fields to remain unplanted. This process enables organic matter
to accumulate and decompose, thus restoring nutrients to the
soil.
Industrial agriculture has dramatically altered the
nutrient management practices used on farms. Modern industrial
farms no longer raise animals and crops together; instead,
livestock are raised on enormous CAFOs (concentrated animal
feeding operations), and crops are mass-produced on separate
farms. Although CAFOs generate tremendous amounts of manure, it is too costly to transport this
manure to other cropland for use as fertilizer.
Instead, today's large-scale industrial farms depend on
synthetic (manmade) chemical fertilizers to support
high-intensity monocrop systems. Unfortunately, synthetic
fertilizers are often over-applied to cropland. In fact, it is
estimated that only about half of all fertilizers are actually
absorbed by plants; the remaining chemicals pollute the atmosphere, soils, and waterways.xiv
In 1998, the U.S. used about 20 million tons of chemical
fertilizers.xv
The enormous amount of manure generated by CAFOs also
causes significant pollution problems. In order to avoid the
expense of treating or transporting this animal manure, CAFO's
typically store the waste in huge open-air pits, or "lagoons,"
and eventually spray the untreated liquid manure onto
surrounding land.
The over-application of synthetic fertilizers and manure
both contribute to the growing problem of nutrient pollution.
Too Many Nutrients!!
Plants need nutrients to grow - but there's a limit to the
amount of nutrients they can actually use. Although plants are
able to absorb some of the nutrients provided by synthetic
fertilizers or manure, when too much chemical fertilizer or
manure is applied, excess nutrients remain in the soil. These
nutrients are eventually washed out of the soil and into ground
and surface waters. The two major nutrient pollutants released
by chemical fertilizers and manure are nitrogen (N) and
phosphorus (P).
Nutrient Pollution
Nutrient pollution damages aquatic ecosystems by stimulating the
rapid growth of algae. This reduces the aesthetic and
recreational values of waterways, and harms many other living
organisms. When the algae die, the process of decomposition uses
oxygen dissolved within the water - this oxygen depletion
eventually kills fish and other aquatic organisms.
According to the 1998 National Water Quality Inventory
conducted by the EPA, 30 percent of surveyed rivers, 44 percent
of surveyed lakes, and 23 percent of surveyed estuaries were
contaminated with unsafe levels of nutrient pollution.xvi
Nutrient pollutants washed from agricultural soils also
degrade coastal environments - in fact, more than 60% of U.S.
coastal rivers and bays are moderately or severely damaged by
nutrient pollution.xvii Excess nutrients degrade
coral reefs and seagrass beds, reduce aquatic biodiversity,
induce algal blooms, and cause tremendous fish kills.xviii
Nutrient pollution is also thought to induce outbreaks of
Pfiesteria.xix This toxic dinoflagelate (type of
algae) emits a toxin that breaks down the skin tissue of fish,
causing bleeding sores or legions.xx Pfiesteria
outbreaks have caused major fish kills and are thought to cause
memory loss, confusion, respiratory problems, and skin problems
in humans.xxi
Nitrogen Pollution and
Human Health
Nutrient pollution also affects human health by contaminating
local water supplies. Nitrogen-contaminated groundwater is
harmful to humans, particularly to vulnerable populations such
as children, the elderly, and people who have suppressed immune
systems.xxii Infants who drink water contaminated
with nitrates can suffer from methemoglobinemia, or blue baby
syndrome, a condition that can cause brain damage or death. The
Centers for Disease Control (CDC) has also linked high levels of
nitrates in drinking water to spontaneous abortions in women.xxiii
Additional Soil Damage
Caused by Synthetic Fertilizers and CAFO Manure
Although synthetic fertilizers add necessary nutrients to
cropland, unlike manure, they fail to restore organic matter to
the soil and have been shown to adversely affect soil
productivity. Regular use of synthetic fertilizers causes
long-term depletion of organic matter, soil compaction, and
degradation of overall soil quality.xxiv
Over-fertilization also causes important minerals such as
calcium, magnesium, and potassium to gradually leach out of the
soil.xxv
Manure from CAFOs can also degrade soil quality. For
instance, since heavy metals are added to animal feed in order
to promote growth, manure can contain trace amounts of metals
such as arsenic, copper, selenium, and zinc.xxvi The
high concentration of manure in CAFO lagoons enable heavy metals
to accumulate in the surrounding environment, contaminating
soil, poisoning wildlife, and polluting groundwater.xxvii
CAFO manure also contains disease-causing pathogens and
residues of hormones and antibiotics. When untreated manure is
applied to fields, these substances can be washed over and
through soil, contaminating groundwater and surface water.
For more information about the damages caused by CAFOs,
see the Environment and Public Health Threats pages.
Sustainable Nutrient
Management
Sustainable nutrient management techniques allow farmers to
maintain healthy, productive soils for crops without degrading
the environment.
Small-scale sustainable farms are able to recycle
nutrients by fertilizing their crops using compost and manure
produced by their livestock. While CAFOs raise hundreds or
thousands of animals, producing far too much manure to be safely
absorbed by the surrounding land, sustainable farms only raise
small numbers of animals, creating just enough manure to
fertilize crops without polluting the environment or
jeopardizing human health.
This enables sustainable farms to avoid using harmful
chemical fertilizers. Natural fertilizers (fertilizers composed
entirely of organic materials such as manure and compost) have
been shown to cause much less pollution than synthetic
fertilizers. One ten-year study of maize fields revealed that
fields treated with chemical fertilizers released 60% more
nitrates into groundwater than fields treated with natural
fertilizers.xxviii
The USDA currently requires all Certified Organic produce
to be grown without synthetic fertilizers. Likewise, organic
meats must come from animals that were fed organic crops grown
without chemical fertilizers.
Cover Crops
Sustainable farmers have also increased nutrient levels in the
soil by growing cover crops such as rye, buckwheat, hairy vetch,
clover, cowpeas, millet, and forage sorghums.xxix
When planted after harvests and chopped into no-till mulch,
these cover crops help add organic matter and nutrients to
fields, thereby reducing the amount of fertilizer required to
grow additional crops in the future.
Soil Fertility Benefits
of No-Till Systems
In addition to providing the erosion-reduction benefits
described above, no-till systems can be used to increase soil
fertility. No-till systems help soils retain moisture, decrease
water runoff, prevent soil from crusting, and increase the
long-term accumulation of organic matter.xxx
Furthermore, no-till soils are able to retain more oxygen since
they aren't compacted by the heavy machinery used in
conventional systems.xxxi
Did You Know?
- Wind erosion can transport soil particles thousands of
miles; soil particles from Africa have been found as far as
Brazil and Florida.xxxiv
- Since wind erosion releases fine dust particles into
the air, it poses a potential threat to human health.xxxv
- Every year, the U.S. spends more than $520 million to
dredge waterways clogged with soil sediment.xxxvi
- In 2002, no-till planting systems were used on more
than 55 million acres of land in the U.S. - almost 20 % of
total planted land.xxxvii xxxviii
- Nitrogen and phosphorus pollution is the primary
source of damage to coastal waters in the U.S.xxxil
- Nutrient pollution has created an oxygen-depleted
"dead-zone" in the Gulf of Mexico. This 7,700 square mile
section of water (an area approximately the size of New
Jersey), is now devoid of aquatic life.xxxl
- In the U.S., approximately 40% of all chemical
fertilizers applied to fields eventually changes into ammonia
and is released into the atmosphere.xxxli
- The U.S Fish and Wildlife Service estimates that in
1995, 37% of all nitrogen and 65% of all phosphorus inputs to
watersheds in the central U.S. were derived from manure.xxxlii
What You Can Do
- Ask your
local farmer about the erosion prevention techniques and
nutrient management methods used on his or her farm - does the
farmer minimize erosion by avoiding excessive tillage
(plowing), or by using no-till techniques? Does he or she use
organic fertilizers instead of synthetic fertilizers?
- Purchase USDA
Certified Organic products; these foods must be produced
without the use of synthetic fertilizers. Or find a sustainable
farmer who does not use chemical fertilizers.
- Plant your own garden. Try making your own organic
fertilizer using a compost bin. Find out how to compost at How
To Compost.org
- Avoid using fertilizers on your lawn. If you must use
fertilizers, chose low-phosphorus varieties.
- Visit the Eat Well Guide to find stores, farms and
restaurants that supply sustainable meats and produce.
For More Information
- Conservation Technology Information Center
- CTIC is a national, nonprofit public-private partnership that
works to promote soil and water quality. Their site includes
technical documents, as well as educational activities for
teachers.
- DiscoverySchool.com - The Dirt on Soil
Created by the Discovery Channel, this website provides a
useful introduction to soil; a great resource for kids and
teachers.
- Living Soils - Maintained by the
Department of Environmental Soil Science at The University of
New England in Australia, this user-friendly site provides an
excellent overview of the living organisms that exist within
soils. Includes many diagrams and photos!
- National Sustainable Agriculture Program -
Soils and Compost This site provides a number of useful
technical documents about agricultural soil quality, soil
conservation, compost, and manure.
- National Resources Conservation Service
(NRCS) Soil Quality site - Includes a wealth of technical
information about soil types, soil quality, and the assessment
of soil quality
Sources
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