On This Page:
Pollution & Damage Caused by Erosion
Soil Nutrients and Fertilizer
Too Many Nutrients
Nitrogen Pollution and Human Health
Sustainable Nutrient Management
Soil Fertility Benefits of No-Till Systems
Did You Know?
What You Can Do
For More Information
“A nation that destroys its soil destroys itself.” - Franklin D. Roosevelt 1
Healthy soil is essential for the production of crops used to feed humans and livestock. In addition to providing a stable base to support plant roots, soil stores 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 has 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.
Erosion is the movement of soil by water, wind or gravity. Although this process occurs naturally, industrial farming practices have dramatically increased the speed at which agricultural soils are eroded. Currently, the average rate of soil erosion on US cropland is seven tons per acre per year. 3
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. In fact, over the past 40 years, 30 percent of the world’s arable land has become unproductive as a result of erosion. 4
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. 5
The National Sustainable Agriculture Information Service notes that erosion is the single greatest threat to soil productivity. 5 According to a 2006 study published in Science, the loss of soil and water from US cropland decreases productivity by about $37.6 billion per year. 6
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 and 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 US. 7
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. 8
Erosion can be significantly reduced through sustainable agricultural practices. The most effective way to prevent erosion is to protect soil from rain and wind by covering it with plants and/or decaying organic matter.
While industrial farms lose tons of soil because of intensive tillage (plowing), sustainable farmers have successfully reduced erosion by adopting conservation tillage techniques. No-till, mulch-till, and ridge-till 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. 9
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. 9 According to the Conservation Technology Information Center (CTIC), conservation tillage enables US farmers to save 306 million gallons of fuel each year, reducing annual greenhouse gas emissions by over one billion pounds of carbon dioxide. 10
Sustainable farmers also reduce erosion by creating buffer strips within fields. Wind erosion can be limited 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.
Plants need more than just sunlight and water. In order to grow, they require a variety of different nutrients. 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.
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. Today, industrial farms no longer raise animals and crops together; instead, livestock are raised on enormous concentrated animal feeding operations (CAFOs ), and crops are mass-produced on separate farms. Although CAFOs generate tremendous amounts of manure, it’s too costly to transport it 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’s estimated that only about half of all fertilizers are actually absorbed by plants; the remaining chemicals pollute the atmosphere, soils and waterways. 12 In 1998, the US used about 20 million tons of synthetic fertilizers. 13
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, CAFOs 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.
Plants need nutrients to grow. but there’s a limited amount of nutrients they can actually use. Although plants are able to absorb some of the nutrients provided by synthetic fertilizers or manure, excess nutrients remain in the soil when too much is applied. These nutrients are eventually washed out of the soil and into ground and surface waters. The two major nutrient pollutants released by synthetic fertilizers and manure are nitrogen (N) and phosphorus (P).
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 2004 National Water Quality Inventory conducted by the EPA, 44 percent of surveyed streams and rivers, 64 percent of surveyed lakes, and 30 percent of surveyed estuaries were considered “impaired,” with “agricultural activities, such as crop production, grazing, and animal feeding operations” cited as the number one cause. 14 A 2008 study by the University of Kansas found that the pollution of fresh water by agricultural nutrients costs at least $2.2 billion per year, at least $44 million of which is spent exclusively on protecting aquatic species from nutrient pollution. 15
Nutrient pollutants washed from agricultural soils also degrade coastal environments. In fact, more than 60% of US coastal rivers and bays are moderately or severely damaged by nutrient pollution. 16 Excess nutrients degrade coral reefs and seagrass beds, reduce aquatic biodiversity, induce algal blooms and cause tremendous fish kills. 18
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. 19 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. 20
Additional Soil Damage Caused by Synthetic Fertilizers and CAFO Manure
Although synthetic fertilizers add necessary nutrients to cropland, they fail to restore organic matter to the soil as manure does, 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. 5 Over-fertilization also causes important minerals such as calcium, magnesium and potassium to gradually leach out of the soil. 21
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. 20 The high concentration of manure in CAFO lagoons enables heavy metals to accumulate in the surrounding environment, contaminating soil, poisoning wildlife and polluting groundwater. 20
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.
Sustainable nutrient management techniques allow farmers to maintain healthy, productive soil for crops without degrading the environment.
Small-scale sustainable farms are able to recycle nutrients by fertilizing their crops using compost and manure produced naturally 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 enough manure to fertilize crops without polluting the environment or jeopardizing human health.
This enables sustainable farms to avoid using harmful synthetic fertilizers. Natural fertilizers, made 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 synthetic fertilizers released 60% more nitrates into groundwater than fields treated with natural fertilizers. 24
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 synthetic fertilizers.
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. 5 When planted after harvests and chopped into no-till mulch, cover crops help add organic matter and nutrients to fields, thereby reducing the amount of fertilizer required to grow additional crops in the future.
In addition to helping to reduce erosion, no-till systems can increase soil fertility. They help soil retain moisture, decrease water runoff, prevent crusting and increase the long-term accumulation of organic matter. 5 No-till soils are also able to retain more oxygen since they aren’t compacted by the heavy machinery used in conventional systems. 5
What is Soil?
It’s not just dirt! Soil is a mixture of minerals, air, water and organic materials, such as roots, decaying plant parts, fungi, earthworms, bacteria and microorganisms. An acre of healthy topsoil can contain 900 pounds of earthworms, 2,400 pounds of fungi, 1,500 pounds of bacteria, 133 pounds of protozoa, 890 pounds of arthropods and algae and in some cases, small mammals. 5
Know Your Soil Lingo
Organic matter: any part of a plant or animal, either living or dead; leaves, roots, sticks, fruit, seeds, worms, insects, manure and food scraps are all examples of organic matter. The decomposition of organic matter provides soils with the nutrients required by plants to grow. Organic matter also improves soil structure, and helps the soil to retain more water. 5
What is Non-point Source Pollution?
NPS pollution is any form of pollution that doesn’t enter the environment through a single, distinct source such as an industrial waste pipe, a smokestack or a sewage treatment plant. Instead, NPS pollution is generated by numerous sources and carried over and through the ground by snowmelt or rainwater. NPS pollutants include eroded sediment, pesticides, fertilizers and toxins from urban runoff.
Scientists have determined that the following 16 elements are essential for crop growth: 32
Know your Soil Lingo
Natural fertilizer: fertilizer composed entirely of organic matter such as manure and compost. USDA "Certified Organic" produce can only be grown using natural fertilizers (no synthetic fertilizers may be used).
Manmade fertilizer manufactured by the chemical industry, composed primarily of nitrogen, phosphorus and potassium, but lacking the organic matter in natural fertilizers.
A nutrient-rich mixture of decaying organic matter (typically leaves and other plant parts) used as fertilizer for plants.
Bring Back the Worms
Conservation tillage, an agricultural practice that minimizes soil disturbance by eliminating or reducing tillage (plowing), helps to increase soil fertility by preserving populations of important living organisms such as earthworms, arthropods and microorganisms. Earthworms have been shown to increase rates of water absorption and retention within the soil, reduce erosion and stimulate underground nutrient cycling, making nutrients available to plants. 5 While deep and frequent tillage can reduce worm populations by as much as 90%, no-till crop systems allow these organisms to thrive. 5