“A nation that destroys its soils destroys itself.” - Franklin D. Roosevelt i
source: http://www.sustainabletable.org/issues/soil/
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
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
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 ControlErosion 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 FertilizerPlants 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 PollutionNutrient 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 HealthNutrient 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.xxiiInfants 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 ManureAlthough 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 ManagementSustainable 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 CropsSustainable 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 SystemsIn 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
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