More Erosion Is Happening Globally. Here’s What It Means For Farms.
Jo Handelsman, Obama’s former science advisor, explains why more farms are experiencing erosion, and how it reduces crop yields.
The following is an excerpt from A World Without Soil: The Past, Present, and Precarious Future of the Earth Beneath Our Feet by Jo Handelsman.
A World Without Soil: The Past, Present, and Precarious Future of the Earth Beneath Our Feet by Jo Handelsman
Some of the worst erosion in the United States is in the Midwest, where our valuable Mollisols are concentrated. It was during a phone call from the White House about water erosion in Iowa with soil scientist Rick Cruse that I began to realize that soil erosion is in fact a slow-burning national crisis for the United States. The state of Iowa illustrates erosion’s impact in the United States. Situated on land that was midwestern prairie before it was farmed, Iowa’s Mollisols support intense cropping systems and high yields. Iowa generates the second highest agricultural revenue among the 50 U.S. states for its production of corn, soybeans, and pork. As an exporter of about $11 billion of agricultural commodities annually, Iowa is a prominent player on the world stage. If it were a country, Iowa would be the fourth largest producer of corn and soybeans worldwide!
Despite Iowa’s relatively gentle slopes, the state has lost enough soil to see disturbing yield reductions, and the projections for the future are bleak. In 2007, Iowa reported that 4 million hectares had each lost 11 tonnes of topsoil and an additional 2.4 million hectares had eroded at twice that rate. The amount of land eroding in Iowa and Ukraine is about equal, but Iowa’s topsoil is less than one-tenth the depth of Ukraine’s and is much closer to hitting subsoil. In fact, bare parent material, exposed by erosion of topsoil, is visible in many locations across Iowa. Overall, Iowa’s annual erosion rate is roughly equivalent to the world average and 10 times the rate of soil genesis. More disturbing are the rates of 55 tonnes of soil per hectare annual loss from 200,000 hectares and 220 tonnes per hectare on 55,000 hectares. Without intervention, this land would be devoid of topsoil in 40 years and some much sooner. Even before bottoming out, crop yields decline as the soil loses fertility and depth. The financial costs of erosion in Iowa are growing, predicted to reach $315 million in 10 years and $735 million after 15 years. Depressed yields will be as unevenly distributed as erosion itself; the financial security of farms losing 50 tonnes per hectare annually will suffer more than those experiencing negligible erosion. Farming is a precarious business in much of the world, and Iowa is no exception. With profit margins of 4-13% in Iowa agriculture, even small yield losses can undermine a farm’s financial stability; large losses are untenable. In many regions, including the Midwest, soil depth appears to drive yield. A study in Ohio reported that removing the top 20 centimeters of soil reduced maize yield by 50%. The dependence of yield on soil makes for a gloomy outlook for Iowa’s farms experiencing erosion.
Unfortunately, the rate of erosion in Iowa is only set to increase. Climate trends over the past 70 years show a steady increase in frequency of severe storms, which is likely to intensify in the next decades. Hard rainstorms will drive soil off Iowa slopes ever more rapidly, making it probable that the state average will rise and hastening the arrival of the day when swathes of Iowa’s Mollisols are reduced to rubble that cannot sustain crop production.
Soil erosion affects more than crop yields in the Midwest. Off-site impacts such as fouled waterways and contaminated drinking water are costly and environmentally damaging. Eroded soil and soluble nutrients are funneled from midwestern farmland into a network of rills, gullies, and streams that drain into the Mississippi River. Along its meandering trek from its origin in Minnesota through the northern agricultural region of Iowa, Wisconsin, Illinois, and Missouri, and southward through Arkansas, Tennessee, Mississippi, and Louisiana, the behemoth gathers nutrients in the water from farm runoff, or bound to soil particles, during its inexorable move toward the sea. By the time it spills into the Gulf of Mexico, the river is brown with silt and loaded with nitrogen and phosphorus. The nutrients cause explosions of algal populations, disrupting the ecosystem. What follows is far worse. The algae are photosynthetic and therefore produce oxygen, but they die and are devoured by microorganisms that guzzle oxygen at fantastic rates, thereby starving other aerobic organisms. Today, the region of the Gulf fed by the Mississippi River is among the largest oxygen-free, or hypoxic, zones in any ocean, covering an area roughly comparable to the size of Israel, Belize, or Djibouti.
The hypoxic zone in the Gulf of Mexico has devastated the local fishing industry, which is worth almost $1 billion. The accrued cost of remediation attempts by the U.S. Environmental Protection Agency (EPA) are substantial—$6.5 million in 2017 alone. Since 2008, the EPA has focused on preventing nutrients from ever entering the Mississippi River and mitigating the effects of those that do. Despite the EPA’s ongoing work with farmers, tribal leaders, and universities from Minnesota to the Gulf, programs intended to reduce runoff and erosion have not shrunk the hypoxic zone. The EPA’s original goal was to reduce the zone from 18,000 to 5,000 square kilometers by 2035, but by 2017, the zone had expanded to 22,000 square kilometers. One group of scientists estimated that a $2.7 billion annual investment would be needed to achieve the agency’s goal.
The most obvious erosion in the United States happens along coastlines and lake shores. Battering storms and rising sea levels have caused cliffs to collapse along California’s coast, threatening life and property. Violent waves regularly take chunks out of Nantucket Island, the Rockaways, and beaches of mid-Atlantic states, which are receding as much as 20 meters each year. Inland, Lake Michigan reached high-water levels in 2018 and 2019. Record waves generated by the same harsh storms that erode midwestern soil are destroying fragile ecosystems along Lake Michigan’s shores in such places as Indiana Dunes National Park, one of the country’s top 10 national parks for biodiversity. The visual drama of coastal erosion makes for compelling news stories, heightening local and national concern about this exigent threat. Soil erosion in farmland, however, happens quietly and steadily. It garners less public attention, but it is just as deadly.
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Crossing the equator, we arrive in South America, the continent predicted to incur the largest increase in erosion rates in the coming decades. Already 68% of South American soil is affected, with 259 million hectares deforested, 70 million hectares overgrazed by livestock, and as much as half the land in Argentina and Paraguay damaged by desertification. Landlocked Bolivia, where 77% of citizens live in degraded areas, is a particularly troubling case. Traditional farming techniques have long protected soil on Bolivia’s slopes—home to the highest proportion of indigenous people in any South American country—but the trend in rural communities toward non-agricultural employment has led to labor shortages, necessitating less labor-intensive crop management practices that accelerate erosion. Although 60% of Bolivian drylands are eroding at 5 tonnes per hectare or less, as much as 6.4% of the land is losing between 50 and 500 tonnes per hectare annually. Few societies can afford losses of that magnitude, which, if left undeterred, will render those lands agriculturally obsolete in a few years.
In Brazil, demand for bioenergy crops indirectly imperils the soil. Brazil has 32 million hectares of land designated as erosion hotspots because they lose soil at more than 20 tonnes per hectare each year. In the southern region, which is mixed forest and a center for poultry and pork production, erosion will likely increase as temperatures rise, leading to high-erosivity rainfall. The Brazilian economy depends on agribusiness to contribute 22% of the GDP and one-third of all employment. Brazil’s diverse crop portfolio, dominated by beef, soybeans, coffee, and orange juice, is exported to China, the United States, and the European Union. Although agricultural expansion has boosted the nation’s economy, it has been destructive to soil. Satellite imagery of Brazil shows that between 2000 and 2014 vast tracts of pastures were replaced with soybeans, sugarcane, and maize, nearly doubling the land area dedicated to intensive row crops. These three crops are responsible for an estimated 28% of Brazil’s soil erosion caused by agricultural activity. Sugarcane production for the bio-energy industry is especially problematic because the soil is left bare and then plowed using heavy machinery that compacts land, increasing runoff and erosion. If Brazil is to keep up with increasing global demand for bioenergy alternatives to fossil fuels, farmers must restore the earth. Already, nutrient replenishment costs sugarcane farmers as much as $6 per hectare each year, and some Brazilian states are paying in excess of $200 million annually to address soil loss. Heavy use of fertilizer will prop up yields temporarily, but before long, damage to soil will reduce crop production.
As soil erosion intensifies worldwide, many countries may experience crop loss simultaneously, creating unprecedented food shortages.
Historically, during times of scarcity after crop failures, natural disasters, or armed conflict, countries have relied on the safety net of international food aid. But food aid programs are predicated on the assumption that certain countries will always have substantial food stockpiles. This assumption may no longer be valid.
Excerpted from A World Without Soil: The Past, Present, and Precarious Future of the Earth Beneath Our Feet by Jo Handelsman with research and creative contributions by Kayla Cohen, to be published November 23, 2021 by Yale University Press. Copyright © 2021 by Jo Handelsman.
Jo Handelsman is a soil scientist, director of the Wisconsin Institute for Discovery, and author of A World Without Soil: The Past, Present and Precarious Future of the Earth Beneath Our Feet. She’s based in Madison, Wisconsin.