Soil Erosion

The loss of topsoil to wind, rain, and other forces is a natural process, but when intensified by human activity, it can have negative environmental, societal, and economic impacts.

 

 

What Is Erosion?

Erosion is a geological process in which earthen materials (i.e., soil, rocks, sediments) are worn away and transported over time by natural forces such as water or wind; sometimes this is sped up by poor management or other human impacts on land. The natural process of river erosion, in fact, created the Grand Canyon, as the Colorado River cut deep and wide through the rock over millions of years, and glacial erosion carved Yosemite National Park’s iconic landscape. (The difference between weathering and erosion is that in the process of weathering, materials are worn away but not transported. And erosion is the opposite of deposition, when natural forces leave earthen materials behind.)

Soil erosion refers to the erosion of the top layer of dirt known as topsoil, the fertile material vital to life. The rate of soil erosion depends on many factors, including the soil’s makeup, vegetation, and the intensity of wind and rain. Because our own activities can also influence the speed of soil erosion, we have the power (and the responsibility) to solve one of the planet’s greatest environmental challenges.

Why Is Soil Erosion Such a Big Problem?

Soil is a natural resource that may look robust and endless, but is in fact the fragile product of thousands of years of formation. Topsoil, which lies closest to the surface of the land, contains essential nutrients for crops. It is this layer of soil that is endangered by wind and water erosion. Soil erosion decreases soil fertility, which can negatively affect crop yields. It also sends soil-laden water downstream, which can create heavy layers of sediment that prevent streams and rivers from flowing smoothly and can eventually lead to flooding. Once soil erosion occurs, it is more likely to happen again.

This is a global problem. Soil is eroding more quickly than it is being formed, causing land to become unsuitable for agriculture – a particularly serious concern in a world where the population is expected to top 9 billion by midcentury. Smarter land management is a necessity.

What Causes Erosion?

Soil erosion occurs primarily when dirt is left exposed to strong winds, hard rains, and flowing water. In some cases, human activities, especially farming and land clearing, leave soil vulnerable to erosion. For example, when farmers till (plow) the soil before or after growing a season of crops, they may leave it exposed to the elements for weeks or months. The overgrazing of farm animals like cattle and sheep can also leave large areas of land devoid of ground-covering plants that would otherwise hold the soil in place. Another practice that has devastating consequences for soil health is deforestation, particularly clearcutting, a widespread practice of the industrial logging industry. When trees are cleared away, the land is left exposed to wind and rain without the security of roots to prevent the soil from being swept away.

Climate is also a major driver of erosion. Changes in rainfall and water levels can shift soil, extreme fluctuations in temperature can make topsoil more vulnerable to erosion, and prolonged droughts can prevent plants from growing, leaving soil further exposed.

How Does Soil Erosion Affect Climate Change?

Erosion degrades land, which means it can support fewer plants that can take in climate-warming carbon dioxide. Soils themselves could potentially sequester enough greenhouse gases in a year to equal about 5% of all annual human-made GHG emissions. Better land management can help keep soils intact so they can grow more carbon-sucking vegetation. This is already happening in China, where the Grain-for-Green project in the Yellow River basin conserved soil and water and reduced carbon emissions.     

On the flip side, unchecked climate change can worsen erosion. A report from the Intergovernmental Panel on Climate Change (IPCC) found that when cultivated without conservation practices, soil is currently eroding up to 100 times quicker than it’s forming.  The risk of erosion will become even higher in the future due to emissions-driven temperature changes, with resulting decreases in agricultural production, land value and human health.

Impacts of Erosion

Soil erosion reduces the quantity and the quality of soil ecosystems and arable land (land that can be used to grow crops). Scientists estimate that in the Midwest, home to some of America’s most productive farmland, half of all topsoil loss has occurred in the last 50 years due to erosion intensified by human activity. According to the NRCS, cropland across Iowa has lost an average of 6.8 inches of topsoil since 1850. And soil erosion in the United States costs the country about $37.6 billion in productivity losses each year. Unmitigated, severe soil erosion can result in the loss of food crops, negatively impact community resiliency and livelihoods, and even alter ecosystems by reducing biodiversity above, within, and below the topsoil.

Where does the soil go? According to agriculture researchers, about 60 percent of soil that is washed away ends up in rivers, streams and lakes, along with whatever has been applied to that soil, including agrochemicals and other pollutants that can contribute to harmful algal blooms and polluted waterways. Dirt that enters water bodies can also clog their natural flow and increase flooding along the waterways. Soil that doesn’t make it all the way from farm fields to waterways can end up being deposited in neighboring areas.

 

We’re already seeing the risks of soil erosion play out around the world. Jakarta’s deadly floods earlier this year are a prime example. Eroded sediments from further upstream clogged Jakarta’s rivers and canals, causing them to overflow. Similar erosion-related floods have occurred in many other countries, such as Colombia, India, the Philippines and Democratic Republic of the Congo.

Soil erosion is not only an environmental issue; it also causes huge losses to the economy. One study estimated global economic losses from soil erosion to be around $8 billion, due to reduced soil fertility, decreased crop yields and increased water usage. In Java, Indonesia, soil erosion is responsible for a 2% loss in total agricultural GDP, taking into account the losses farmers face directly and the losses others face downstream. Another study showed that soil erosion in Sleman, a district located in Java, costs 17% of an average farmer’s net income per hectare of agricultural land.

The U.S. agricultural sector loses about $44 billion per year from erosion. This value includes lost productivity, along with sedimentation and water pollution. Lost farm income is estimated at $100 million per year. Soil erosion also costs European countries $1.38 billion in annual agricultural productivity losses and $171 million in lost GDP (about 1% of total GDP). South Asia loses $10 billion annually thanks to soil erosion.

 

Erosion Control Methods and Practices

Below are some common strategies for effective erosion control, many of which are part of the philosophy of regenerative agriculture. It’s worth noting that finding appropriate erosion-control treatments relies on understanding which specific erosion processes are at play.

• Build soil organic matter: To be healthy, soil needs just the right mixture of water, air, minerals, and organic matter. Soil organic matter, made up of decomposing plant and animal material, is the glue that helps bind soil together and keeps it anchored in place. Research suggests that increasing organic matter from 1 to 3 percent can reduce erosion by 20 to 33 percent because it increases the water-holding capacity of soil.
• Plant vegetation: Trees, shrubs, hedgerows, and ground plants can block corrosive wind. Ensuring uninterrupted ground cover, such as through planting cover crops, also helps bind soil to roots.
• Use erosion control matting: Also known as an erosion control blanket, this ground covering is often made of open-weave, biodegradable materials that shield the soil and provide support for growing vegetation on bare ground. This erosion control method is often effective for solar farms and construction sites where large areas are left barren and vulnerable to wind and water erosion.
• Practice no-till/minimal tillage: Farmers have been plowing farm fields for centuries, but in recent decades agriculture scientists have helped prove that a no-tillage approach may offer more benefits. By not disturbing soil, farmers have been able to reduce erosion and runoff, which benefits crop productivity and water quality. No-till practices can also help reduce the loss of nitrogen and other vital soil nutrients.
• Use grazing practices that reduce erosion: Rotational grazing is a method that moves livestock from one pasture paddock to the next. Each paddock gets a rest period and is allowed to regrow undisturbed, which minimizes soil compaction and erosion. Other beneficial practices include installing fencing and stream crossings to keep pastures safe from degradation.

What Solutions Exist to Prevent Soil Erosion?

1. Use Soil-friendly Agricultural Practices

Terraced farming needs to be implemented to make hillside agriculture manageable. Terraces prevent erosion and allow more water to flow to crops. In addition, hillside farm fields need full crop cover to help keep the soil in place. This can be accomplished by intercropping, which means growing two crops together in the same field, such as planting rows of maize or soybean between rows of oil palm trees. For smallholders, agroforestry systems where a diverse set of crops, including trees, are grown together can be effective. Access to manure improves the organic matter of the soil, which inhibits erosion. Finally, alternating deep-rooted and shallow-rooted crops improves soil structure and reduces erosion at the same time.

2. Offer Incentives for Land Management

Although the science of sustainable land management has been gaining support, the socio-economic context often makes implementation difficult. Sustainable land practices need to be financially viable for farmers. Anti-erosion measures have a median cost of $500 per hectare, a considerable investment for a farmer. Governments and banks must help farmers get access to credit and support in implementing erosion prevention. This is not only a good deal for the farmer, but for the whole community. The cost of erosion prevention is far lower than the price of land restoration and rehabilitation, which one source estimated to be around $1,500–$2,000 per hectare. Another source found it could reach $15,221 per hectare.

3. Prevention AND Rehabilitation

The key to managing and reducing soil erosion is to rehabilitate already-damaged land, stop further degradation and put erosion-preventative measures at the core of land management policy. In this way, we can help prevent hunger and mitigate the climate crisis.

To learn more about WRI's work restoring eroded soils, click here.