Why We Should all Worship the Ground We Walk On
It's one of nature's most perfect contradictions: a substance that is ubiquitous but unseen; humble but essential; surprisingly strong but profoundly fragile. It nurtures life and death; undergirds cities, forests and oceans; and feeds all terrestrial life on Earth. It is a substance few people understand and most take for granted. Yet, it is arguably one of Earth's most critical natural resources—and humans, quite literally, owe to it their very existence.
From the food we eat to the clothes we wear to the air we breathe, humanity depends upon the dirt beneath our feet. Gardeners understand this intuitively; to them, the saying "cherish the soil" is gospel. But for the better part of society, dirt barely gets a sideways glance. To most, it's just part of the background, something so obvious it's ignored.
Even among the environmentally minded, soil sags well below the radar of important causes. But therelationship between soil quality and other aspects of environmental health is intricately entwined. What's more, it's a relationship that encompasses a vast swath of territory, from agricultural practices to global climate change, and from the well being of oceans to that of people.
Despite humankind's long relationship with soil, the stuff remains a mystery. Even our language manages to maligns it. Somehow, "dirt" has acquired a bad reputation. And it's been codified in some of our most common idioms, with people described as "dirty rotten scoundrels," "poor as dirt" or "dirtbags." The modern word "dirt" itself descends from the less than complimentary Old English word "drit," meaning "excrement." Instead of marveling at the mystery of soil, we have mocked it, by dredging and paving; desiccating and polluting; and working it to exhaustion.
Now our poor husbandry of this essential resource is catching up with us, in the form of disconcertingly rapid erosion and loss of farmland, widespread agricultural pollution, damage to fisheries, and alarming levels of pesticides and other chemicals building up in our bodies. The subject of soil is rarely billed as glamorous or sexy, but it should be. From its remarkable properties to its critical ecological importance, the dirt under our feet is a goldmine of scientific wonderment, and it's about time people got excited about soil.
Soil is Special Stuff
Soil types vary considerably on our planet, from the hottest deserts to the coldest poles. Soil directly and indirectly affects agricultural productivity, water quality and climate. Thanks to the Earth's soils, most of the rainfall hitting our planet is trapped and absorbed, watering plants and replenishing aquifers, rivers, lakes and streams. If soil didn't catch and apportion this water, it would run off the land into the oceans, and the continents would be barren wastelands.
If it weren't for the stabilizing effect of soil, ancestral plants could never have survived the fierce, raw weather of primordial Earth. Over millions of years, these plants and their offspring created the life-sustaining atmosphere required for land animals to evolve. Essentially an organ of Mother Earth, soil is a vital living system—the very skin of our planet—that nourishes the plants we eat, the animals we use for food and fiber, and the thriving underground kingdom of bacteria, fungi, protozoa, earthworms and other microbes that are critical to the planet's food webs.
To put it another way, without soil humans would be creatures of the sea. Only about 20 percent of the Earth's surface is covered by land. However, much of this land is too inhospitable to support our species. Only about eight percent of the planet's soil surface is actually arable. This means, explains Wes Jackson of the Land Institute, that all six billion people living today have but a tiny fraction of soil to thank for their survival and diverse ways of life.
Anatomy of Healthy Soil
So what is healthy soil? Deceptively simple to the naked eye, healthy soils are dynamic ecosystems made up of a mixture of minerals, air, water, organic materials and a healthy population of microorganisms. The range and concentration of minerals present depends on the parent bedrock. Healthy soil is also extremely porous: Air accounts for about half its volume, providing channels for water to flow, pathways for roots and space for organisms to move around. Compaction, primarily the result of heavy farm machinery and livestock, squeezes air out of soil, depleting available oxygen.
When soil is healthy, however, it is a hotbed of thriving biological activity. We can't see most of that ongoing work, save perhaps on particularly rainy days when earthworms flock to the surface or a large insect scuttles across the ground. But a single gram of fertile soil can contain several million microbes. One heaping tablespoon of healthy soil may contain up to nine billion microorganisms, which is more than the human population on Earth, points out Harvey Blatt, author of the 2004 book America's Environmental Report Card. 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, even small mammals. When this diverse soil community is disrupted or damaged, the consequences may be dire.
Plants are the first to suffer from damage to the soil community. Interestingly, soil microbes play a critical role in plant health. Long ago in Earth's evolutionary history, early soil microbes forged one of the first symbiotic relationships with early land plants when some algae and bacteria developed the ability to "fix" nitrogen, a nutrient essential for plant growth. Nitrogen is plentiful in the atmosphere, but plants can't use it in that pure form. They can only use nitrogen that's been incorporated into compounds like ammonia or nitrate. Once nitrogen-fixing organisms evolved billions of years ago, pioneer plants were able to creep onto the land. As these early plants gained a foothold on the rocky ledges poking out of the primordial seas, they helped build the terrestrial soils.
Today, the symbiosis between soil organisms and plants is deeply intertwined. Many soil microbes feed on by-products from growing roots and, in turn, help plants by extracting minerals and vitamins from the soil. Like microscopic farmers plowing and tilling their subterranean plots, these organisms enhance soil structure and help control plant-preying pests, cultivating an underground ecosystem.
These "chthonic" (pronounced "thonic" and meaning "of the Earth") creatures also provide another overlooked but critical function: They are perhaps the world's most prolific recyclers. Without the help of soil microbes to break down decaying plant and animal matter, fertile soils would not exist. Dead animals would never decompose, and the litter of leaves dropped from trees every autumn would soon bury buildings and roads.
The Carbon Link
Soils also play an important role in the process of recycling carbon, the most vital element for living beings. Healthy soils can be an important carbon sink, binding up carbon that might otherwise enter the atmosphere, potentially contributing to global
According to the Environmental Literacy Council (ELC), soils contain twice the amount of carbon found in the atmosphere, and three times more carbon than is stored in all the Earth's vegetation. Thanks to soil microbes, as plants and animals decompose, some of their carbon becomes part of the organic matter in soils instead of escaping into the atmosphere as carbon dioxide. Paul Hepperly of the Rodale Institute's experimental research farm in eastern Pennsylvania defines organic matter as "mostly the resistant remains of plants." When this material combines with the mucus, slime and digestive products of soil organisms, it forms the material known as humus—an extremely rich component of soil the color of dark chocolate. Hepperly explains that humus is saturated with carbon.
"Carbon is really the glue that holds everything together in fertile soil," Hepperly says. "When you introduce tillage and compaction, there's excess air, and humus breaks from long chains of carbon into carbon dioxide, which then goes into the air." Since humus is highly concentrated organic matter, soils with a lot of humus tend to be more fertile. By the same token, damaged soils have less organic matter, hold less carbon, harbor a much more fragmented community of soil microbes, support fewer plants and animals, and are much more vulnerable to erosion and other problems. "Organic matter is really what holds water in the soil when you have droughts or floods," Hepperly says. "If you take away the glue, everything falls apart."Soils in Trouble
Unfortunately, in many parts of the world, that "glue" is deteriorating rapidly. The explosion in human population, fuelled by agricultural and technological advancements, has led to soil erosion, compaction, salinity and loss of fertility. As the figurative "lifeblood" of many organisms, including humans, problems at the level of soils mayreverberate through entire ecosystems—or civilizations.
In the 1930s, Hugh Hammond Bennett—a USDA scientist widely regarded as the "father of soil conservation" (see sidebar)—commented, "Soil erosion is as old as agriculture. It began when the first heavy rain struck the first furrow turned by a crude implement of tillage in the hands of prehistoric man."
Any discussion about the health of soil ends up addressing agriculture. Since Neolithic times, when our ancestors adopted settled agriculture, our relationship with soil has been intimate and intense. Throughout history, the story has repeated itself: Great civilizations have grown where soils were fertile enough to support high-density human communities, and fallen when soils could no longer sustain our rough treatment. According to the International Task Force on Land Degradation, the great early civilizations of Mesopotamia arose because of the richness of their soils, and collapsed because of declines in soil quality. Poor land management and excessive irrigation caused soils to become increasingly degraded, leading to power struggles, migrations, and ultimately, the collapse of the Fertile Crescent civilizations.
Ancient Greece suffered a similar fate. The philosopher Plato, writing around 360 B.C., attributed the demise of Greek power to land degradation: "[In earlier days] Attica yielded far more abundant produce. In comparison of what then was, there are remaining only the bones of the wasted body; all the richer and softer parts of the soil having fallen away, and the mere skeleton of the land being left."
Many experts also blame the collapse of the great Mayan civilization and the peaceful Harappan society of the Indus valley on soil exhaustion and erosion, resulting from agricultural practices and clear-cutting of forests. According to Jared Diamond, a UCLA professor and author of the books Guns, Germs and Steel and Collapse, 90 percent of the people inhabiting Easter Island in the Pacific died because of deforestation, erosion and soil depletion. In Iceland, farming and human activities caused about 50 percent of the soil to end up in the sea, explains Diamond. "Icelandic society survived only through a drastically lower standard of living," he says. Not surprisingly, the practice of destroying soils by torching or salting farms and fields has been employed by armies in wars, from Alexander the Great to Napoleon.
Today, we are facing many of the same issues as these former civilizations: forest loss, over-consumption, dwindling freshwater supplies, overpopulation and over-worked soils nearing the brink of collapse. While other social and economic factors also threaten soils, intensive, unsustainable agricultural practices continue to bear the brunt of the blame, despite lessons from history. Non-agricultural activities such as logging, construction, off-road vehicles, floods, droughts and fires also increase erosion, but the Natural Resource Conservation Service (NRCS) reports that agriculture is responsible for at least 60 percent of the erosion afflicting the U.S.
In America, our history has arguably been shaped from the outset by unsound farming practices. From the moment the first Europeans stepped off the boat, we set plow to earth and began to dredge the soil, overworking it through constant tilling and planting. "The farming practices of our forebears caused a one percent per year breakdown of essential organic matter, so that in 50 to 100 years families could no longer farm their home plots," explains Hepperly. He adds that the need to seek new fertile soils and farmsteads was a major factor in the westward movement of settlers.
Fortunately for those early colonists, there was always an abundance of fresh, new land. Today, humans have colonized just about every viable land surface on the planet. No fabled fresh frontiers remain. As the world's human population continues to grow, placing ever more strain on already stressed soils, will human societies find themselves near the brink of collapse?
Threats to Soils
Not all soil problems are equal everywhere. In many regions, including the U.S., Australia, China and Mexico, wind and water erosion are major threats. In the arid southwest of the U.S., massive irrigation is causing soils to become salty, in some cases to the point that plants can no longer grow. Soil compaction abounds wherever massive farms or livestock operations (especially confined livestock operations) exist; and in many countries with naturally acidic soils, such as Australia and Ghana, overuse of fertilizers is causing soils to become even more acidic. In the case of Ghana, Hepperly says that the soil has become so unnaturally acidic that it can no longer grow its native sorghum crop. Declining soil fertility—the result of over-intensive farming—is a serious problem worldwide, but it is particularly acute in Sub-Saharan Africa, where severe depletion of soil nutrients is a major cause of poverty and hunger.
Among the soil problems, it is generally agreed that soil erosion is one of the most serious, in part because it often precedes or accompanies other forms of soil degradation or environmental problems. While erosion occurs naturally because of wind, water and ice acting on any exposed rock or soil surface, the process has been tremendously exacerbated by human activities, especially agriculture, logging and construction. It is now estimated that humans are responsible for 60 to 80 percent of all erosion. According to the American Society of Agricultural and Biologi
cal Engineers (ASABE), lost food production is the direst consequence of erosion.
The 1930s Dust Bowl is perhaps the most extreme example of this consequence in modern U.S. history. For nearly a decade between 1931 and 1939, prolonged drought acted on severely misused land to cause massive erosion over millions of acres in southern Great Plains states. Destruction of a significant portion of agricultural acreage caused a mass exodus of millions of people and bogged down an already depressed national economy. According to the United Nations Convention to Combat Desertification, during the Dust Bowl years, "At least five inches of topsoil were lost from nearly 10 million acres."
While erosion isn't as dramatic in the U.S. today as it was in the 1930s, the problem continues to haunt farmers and urban developers. In a 2002 position paper adopted by ASABE, the group estimated that soil erosion is damaging the productivity of 29 percent (112 million acres) of U.S. cropland and is adversely affecting the ecological health of 39 percent (145 million acres) of rangeland. Worldwide, erosion is one of the biggest causes of soil degradation. "An outrageous amount of soil is being lost," says Craig Minowa, an environmental scientist with the Organic Consumers Association (OCA).
In many places, soils are eroding faster than they can be rebuilt. Though a renewable resource in theory, soil forms very slowly, measured in centuries. For all practical purposes, the soil we lose to erosion will never be replaced in our lifetimes.
"The fastest soil regeneration is about 200 years, but it can take a million years, depending on the geologic processes," says Dan Yoder, a professor in the Department of Biological Systems Engineering and Soil Science at the University of Tennessee. "Coarse sand, for instance, doesn't form soil very easily."
Hepperly says that each American erodes an average of 3.5 tons of soil yearly. "In fact, it is our biggest national export," he quips. A single rainstorm can wash away centuries-old accumulations of soil from damaged, neglected or badly managed ground.
Human-caused erosion (also known as "accelerated erosion") is most damaging to topsoil, the soil's uppermost layer. In addition to being the most productive soil layer (it contains the highest concentration of organic material), topsoil is also the layer in which plants grow best. But topsoil is also the thinnest layer, usually not more than a foot deep. Preston Sullivan of the National Sustainable Agriculture Information Service says that soil lost to erosion contains about three times more nutrients and 1.5 to five times more organic matter than the soil that remains behind. Further, loss of topsoil increases a soil's overall vulnerability to erosion, thus creating a vicious, exponentially worsening cycle of damage.
The developing world is especially at risk from the negative effects of soil erosion and declining soil fertility. In Africa, many nations are facing a veritable soil health crisis, due in large part to increasing population pressures, poverty, and the limitations inherent to many tropical soils. Tropical soils are naturally lower in fertility, and also foster increased weeds and pests, says Hari Eswaran, national leader of the NRCS-affiliated Office of World Soil Resources and an expert on soil erosion problems.
"In Nigeria two to three years ago, I visited a farmer growing tapioca, a tuber which is a staple crop there. His average yield was about three tons per acre," Eswaran says. "In contrast, the average yield is 30 tons per acre in India
You combine these problems, and that's why they practiced shifting cultivation. After two years, production decreased and people moved on. That only works with lower population.
Population pressures are now forcing farmers to remain on the same nutrient-depleted land to grow their crops year after year—a practice known as "mining," because nutrients are literally extracted from soil with nothing given in return. Among other problems, farmers often have practically no access to soil-enriching fertilizers.
"Here in the U.S. land starts to degrade and farmers see it in terms of decreased productivity. They counteract it with massive amounts of fertilizers and chemicals," Eswaran says. But in Africa, farmers often have to walk for miles to buy fertilizer, he explains. Many are also ignorant of proper fertilizer use and simple farming techniques that could significantly minimize soil damage. The result is that at least a third of Sub-Saharan Africa's population is chronically undernourished, according to a study released this year by the International Center for Soil Fertility and Agricultural Development (IFDC), a U.S.-based nonprofit. The study tracked soil health across Africa from 1980 to 2004, and describes the situation now facing Africa as a "soil health crisis." Some 75 percent of Africa's farmland is severely degraded and rapidly losing basic soil nutrients needed to grow crops, the report states. Many sub-Saharan countries can't feed themsleves," says Eswaran.
A 1995 study published in Science concluded that the loss of soil and water from U.S. cropland decreases agricultural productivity by about $27 billion per year. A 2000 story in the Australian rural weekly paper Landline estimates that soil degradation costs Australian farmers $2.5 billion a year in lost production. It added that nobody has even calculated the off-farm costs of soil degradation, such as salt-polluted rivers or the loss of biodiversity and wildlife habitat.
When soils erode, much of the displaced sediment—as well as the pesticides and excess nutrients mixed with it—ends up washing into streams, rivers and eventually oceans. The World Resources Institute says that the surfeit of excess nutrients on the land—primarily from a massive surge in fertilizer use since the 1940s, deforestation and the burning of fossil fuels—has resulted in "a glut of nitrogen," the effects of which "reach every environmental domain, threatening air and water quality, and disrupting the health of terrestrial and aquatic ecosystems." The Institute adds, "Aquatic ecosystems have probably suffered the most so far. They are the ultimate receptacles of much of the nutrient overload."
The Environmental Protection Agency (EPA) reveals that at least 40 percent of the affected stream miles and 45 percent of lake and reservoir areas were damaged because of eroded sediments. More broadly, Blatt writes that farms produce 70 percent of all stream pollution in the U.S.
Agricultural pollution originating in the Midwest is the primary cause of a chronic pollution problem in the Gulf of Mexico known as hypoxia. When excess nutrients pollute water, toxic algal blooms grow, which suck up most of the available oxygen. This leads to the death of aquatic organisms. The mouth of the Mississippi River now has a yearly dead zone larger than the size of New Jersey, says Hepperly, and brown shrimp harvests have routinely been 25 percent of their historical catch size. The problem is similar in the Chesapeake Bay.
Erosion isn't just an agricultural phenomenon. Urban erosion is an equally significant problem—one that has often been overlooked, but is becoming more serious as populatio
n pressures fuel development and urban expansion. Housing and construction projects gouge the soil and strip its vegetation, leaving it exposed to the elements for long periods of time. Erosion rates remain higher after construction is completed, as vegetation is reduced and rooftops shed water that would have been trapped by plants. When it rains, the soil washes away like sand from a shovel, eventually finding its way into city sewers and gutters, and eventually, streams and waterways.
"One of the hot areas of soil science is erosion at construction sites," says the University of Tennessee's Yoder. "In agriculture, I think we have a pretty good handle on how to control soil erosion. Construction sites are something else. You have steep slopes, and they're completely bare."
One of the major problems with urban erosion, Yoder explains, is that there is currently no unified national standard for erosion monitoring and control at construction sites. While soil conservation measures on farms were adopted in the 1970s and "80s requiring farmers who receive federal support to prove they had adopted conservation practices, no such regulatory structure exists at construction sites. "You have the EPA watching, but each state has its own agency for permitting of construction sites," Yoder says. "There's not much concentration on soil conservation."
The available statistics on construction site erosion are disconcerting. According to Cathy Rofshus, an administrator for the Shell Rock River Water District in Minnesota, "The Environmental Pollution Control Agency estimates that 20 to 150 tons of soil per acre runs off construction sites with rainwater. That would be 1,600 to 12,000 tons of soil for an 80-acre site." Wal-Mart alone may thus be responsible for between 1.5 million and 11.25 million tons of soil erosion in the U.S. through construction of its stores. According to AlterNet, Wal-Mart's 3,600 U.S. stores and 100 distribution centers, including their parking lots, currently occupy roughly 75,000 acres.
To minimize erosion at construction sites, Yoder says there are a number of fairly simple measures developers can employ. Silt fences can be placed at the bottom of slopes to stop sediment from getting into waterways. A wall of soil may build up behind them, which is then returned to the hillsides. Sediment basins are more permanent versions of these structures that trap run-off and allow the suspended soils to settle out before water carries sediments into streams. Erosion-control mats are usually made out of straw and placed on the tops of slopes so that wind and rain will be less likely to carry soil away. Hydro-mulching is a similar measure whereby a water-seed-straw mix that will absorb rain is blown over the bare land.
The Funding Erodes, Too
Even as soil problems have increased in severity, federal funding of soil research and conservation has steadily declined over the years (see sidebar, "The Lay of the Land"). Where as the government practically lavished money on soil projects in the 1930s and "40s, scientists proposing soil-focused research projects today are having trouble getting funded. They have to compete with research proposals on "hot" science topics that are more attractive to major grantees, or they have to adapt their research to fit the funder's interests, Yoder says.
Staff in Eswaran's World Soil Resources office once traveled extensively in developing countries educating farmers about soil management and providing support. For the past 10 years, however, Eswaran says the office "has had no funds to travel." Most of the direct scientist-to-farmer work once possible with federal funds—primarily from USAID—has had to be aborted. USAID gave Eswaran's office about $65 million in the early 1980s for agricultural research. By the early 1990s, his funding had dropped to about $10 million, a decrease of almost 85 percent.
And yet in some African countries, simple education of farmers in better land management techniques and better access to fertilizers could arrest the worst of problems. In Yoder's view, part of the problem is that "nobody thinks long-term anymore."
Is Bigger Better?
One reason why agriculture can be so detrimental to soils is because of the sheer scale of most farming operations today. According to USDA, since 1900 the number of farms has fallen by 63 percent, while the average farm size has risen by 67 percent. In 1900, the average farm size was less than 100 acres; in 2002 it was more than 400 acres. Farm operations have also become increasingly specialized, from an average of about five commodities per farm in 1900 to an average of one per farm in 2000. Most important, the USDA says that all of this has taken place with no variation in the amount of land being farmed.Small family farms have steadily disappeared in the midst of increasing urbanization and decreasing profitability, and the mega-farms that now dominate U.S. agriculture have transformed into "agribusinesses" that receive most federal farm subsidies. What this means is that the intensity of agriculture has dramatically increased.
While individual farms have shrunk, yields have increased, thanks to growing reliance on pesticides, herbicides and fertilizers. But while this practice has allowed farmers to control pests and nutrients in the short term, the net result is artificial enrichment of overworked soils that often lose stability.
According to David Tilman, who wrote the 1998 Nature article "The Greening of the Green Revolution," only about half of all fertilizers are absorbed by plants. The remaining chemicals pollute the atmosphere, soils and waterways. OCA's Minowa attributes much of this chemical overuse to a comparative detachment of industrial farm workers from the land. "Farmers working their family land knew they'd be working that plot, and their children would be working that plot, for a long time, so they would take care of it and respect it more," he says. "Agribusinesses, on the other hand, are primarily concerned with profitability, which means using the land more intensively."
Yoder cautions against placing all the blame on agribusiness, however. Sustainable management of farms can be expensive, he says, and small farms sometimes can't afford the risk.
Farmers generally apply some fertilizer to their crops, although some are "natural," including cover crops used in winter to help feed nutrients back into the soil. However, most fertilizers employed by conventional farmers are synthetic versions of the NPK (nitrogen, phosphorus, potassium) formula. These nutrients are depleted from intensively worked soils over time. But synthetic fertilizers can also wreak havoc on the underlying ecology, as well as on humans and ecosystems far away from the farms on which they are used. EarthWorks News reported, "The high salt content of many synthetic fertilizers
may overwhelm the natural balance of organic decomposition taking place in the soils."
Like fertilizers, pesticides are often over-applied. According to Blatt, pesticides have become 10 to 100 times more toxic than 30 years ago, which has resulted in about 3.5 to 5 million acute poisonings each year. Farmers who work with certain kinds of pesticides have been found to get Parkinson's disease and severa
l types of cancer more often than the general public. Pesticides have also been linked to learning disabilities, hyperactivity, emotional disorders, weakened immune systems, birth defects and low sperm counts. Further, Blatt says that while less than one percent of pesticides applied to fields actually reach the target pests, at least 53 carcinogenic pesticides are presently applied in massive amounts to major crops. Many of the chemicals developed for agricultural use have not been tested for their effects on humans or are poorly regulated.
For instance, the manufacturers of Atrazine, one of the most commonly used pesticides, recommend that farmers apply two pounds per acre, Hepperly says. However, only half of it breaks down in a year, so at the end of the planting season, one pound still remains through the following year.
Why do farmers continue to apply so much? By recommending that farmers apply more of the pesticide than is needed, the chemical manufacturers reap a bigger profit. What is particularly troubling about Atrazine, though, is that recent studies have linked very low doses to developmental problems in frogs, which are experiencing global declines. Several European countries have now banned the chemical.
Gradually, the world's soils have been accumulating pesticides and fertilizers, and as these soils erode, their chemical burdens pollute the surrounding environment or enter the food supply. According to a Food and Drug Administration (FDA) study, more than 80 percent of conventional, non-organic produce tested in grocery stores had measurable levels of pesticides. Minowa says that most pesticides accumulate for years in people's bodies, collecting in fat cells and other tissues. Children are particularly vulnerable to pesticides, with studies showing numerous detrimental effects to their health.
Hepperly believes our continued use of pesticides and fertilizers has made the soil problems we faced 20 or 30 years ago much more severe. "This can be measured in water quality," he says. "Dead zones in ocean environments have expanded in size and number around the globe."