Topsoil erosion is the loss of the top layer of soil due to natural or human-caused processes. This can lead to a variety of negative consequences that impact agricultural productivity, water quality, and ecosystem health. Understanding why topsoil erosion is problematic is key to promoting better land management practices that conserve this critical resource.
What is topsoil?
Topsoil is the uppermost layer of soil that has the highest concentration of organic matter and microorganisms. It is usually darker in color and has a looser, crumbly texture compared to the subsoil layers beneath it. Topsoil ranges in depth from several inches to a couple feet depending on the ecosystem. It takes approximately 100 to 500 years for just an inch of topsoil to form naturally.
Key properties of topsoil
- Rich in organic matter like decomposing leaves, roots, and organisms
- Holds nutrients and supports microbial activity
- Has good aeration, drainage, and moisture retention
- Anchors plants and supplies them with water and nutrients
Why is topsoil so important?
Topsoil is vital for plant growth and agricultural production for several reasons:
Fertility
The organic matter in topsoil supplies plants with nutrients like nitrogen, phosphorus, and potassium. Decomposing organisms release these nutrients in plant-available forms through the soil food web. Topsoil also has cation exchange capacity that retains positively charged nutrient ions.
Water retention
The loose, crumbly texture of topsoil created by organic matter allows it to effectively absorb and store moisture. This ensures a steady supply of water is available in the plant root zone.
Anchorage
Topsoil provides physical support and anchorage for plant roots. The topsoil particles cling to the roots and keep them stabilized in place.
Biological habitat
The multitude of organisms that live in topsoil form a complex soil food web. This web includes bacteria, fungi, protozoa, earthworms, and more that help with nutrient cycling and soil structure improvement.
How does topsoil erosion occur?
Topsoil erosion occurs when soil particles are detached and transported away by wind or water flows more rapidly than new soil can form. Erosion can occur naturally, but human activities have dramatically increased rates of topsoil loss.
Water erosion
Water from rainfall, flooding, or excessive irrigation can wash soil particles downslope. Bare soil without protective plant cover is most susceptible. Splash erosion occurs when raindrops hit the ground and detach soil, while runoff transports particles downslope into waterways.
Wind erosion
Strong winds can pick up and carry unprotected topsoil particles long distances. Dry, fine-textured soils are most at risk. Wind erosion is most problematic in arid climates.
Tillage erosion
Tillage from plowing and preparing soil for row crops disrupts soil structure and detaches soil particles. These are then transported downhill. Contour plowing helps reduce tillage erosion.
Effects of topsoil erosion
The effects of excessive topsoil erosion include:
- Reduced soil fertility and crop yields
- Land degradation and desertification
- Sedimentation of waterways
- Water pollution from agricultural runoff
- Loss of organic matter and biodiversity
- Increased flooding risk
- Damage to aquatic ecosystems
Why is topsoil erosion bad for agriculture?
Topsoil erosion threatens agriculture productivity and food security. With topsoil loss, soil fertility declines and crop yields decrease. Erosion removes the most nutrient-rich surface layer, leaving behind poorer subsoil. Water retention and drainage decline, making the remaining soil more vulnerable to drought and nutrient leaching.
Loss of soil organic matter
Organic matter is crucial for supplying nutrients, retaining moisture, and improving soil structure. Erosion preferentially removes the organic matter-rich topsoil. This can’t be replaced easily since soil organisms need decades to centuries to rebuild organic matter to previous levels.
Nutrient depletion
Nutrients essential for plant growth like nitrogen, phosphorus, potassium, and micronutrients are lost through erosion. Typically only a fraction of these applied nutrients remain in the soil, so fertilizer must be continually applied to replace losses.
Reduced water storage
With less organic matter, eroded soils have lower water retention. This makes crops more prone to drought, increasing the need for irrigation. However, eroded soils are also more prone to nutrient leaching losses when irrigated.
Soil compaction and structure decline
Erosion removes topsoil’s fine particles responsible for good soil structure. This leaves behind a less porous soil prone to compaction. Dense soils restrict root growth and drainage.
Examples of agricultural erosion impacts
The United States has lost about one-third of its topsoil since farming began. Around 30 percent of the world’s arable land has been lost to erosion over the past 40 years. Such losses have major economic impacts:
- In Ethiopia, crops yields were reduced by 50% on land with severe nutrient depletion and topsoil loss.
- Topsoil erosion in the United States is estimated to cost over $37 billion per year in lost agricultural productivity.
- China has lost 40% of agricultural capacity since 1950 due to erosion. This has reduced national grain harvests by 8%.
Why is topsoil loss bad for water quality?
Eroded topsoil particles that wash into water bodies severely degrade water quality. Excess sediment causes turbidity, harming aquatic plants and animals. Attached to the soil particles are also nutrient pollutants, pesticides, and heavy metals that contaminate water.
Increased sedimentation
Suspended soil particles increase water turbidity, or cloudiness. This blocks sunlight penetration needed by aquatic plants and algae. As particles settle, they smother lake and ocean bottoms, burying eggs and suffocating organisms.
Nutrient pollution
Phosphorus and nitrogen attached to eroded soil particles are major contributors to nutrient pollution in waterways like the Gulf of Mexico hypoxic zone. This stimulates algal blooms and reduces dissolved oxygen levels needed by fish and shellfish.
Contaminants
Other agricultural chemicals like pesticides, antibiotics, and heavy metals are also carried by eroded soils into water systems. These contaminants diminish water quality and pose risks to public health.
Increased expenditures
Sedimentation of reservoirs, lakes, and harbors necessitates costly dredging to maintain water storage capacity and navigability. Water treatment costs also rise to filter sediment and attached pollutants.
Why is topsoil loss detrimental for ecosystems?
Beyond agricultural impacts, topsoil erosion also degrades natural ecosystems. Sedimentation and attached nutrient pollution disrupt aquatic and coastal ecosystems. On land, topsoil loss diminishes soil biodiversity and organic matter crucial to ecosystem functioning.
Harm to aquatic life
Sediment loading and nutrient enrichment from eroded topsoil degrades stream, lake, wetland, and marine habitats. Declining water clarity and oxygen levels alter food webs and stunt biodiversity.
Loss of soil biodiversity
Myriad organisms inhabit healthy topsoil, including microbes, earthworms, insects, and small vertebrates. These organisms regulate soil processes like carbon storage, nutrient cycling, and soil structure improvement. Erosion diminishes habitat space and food sources for soil biota.
Decline of organic matter
Organic matter provides energy, carbon storage, and habitat for soil organisms. With topsoil erosion, organic matter cannot accumulate at natural rates. This disrupts soil food webs and biochemical processes dependent on organic matter.
Increased carbon emissions
Erosion exposes stored organic carbon in topsoil to decomposition. This oxidation releases carbon dioxide into the atmosphere, contributing to climate change. Up to 1.14 billion tons of carbon may be liberated per year globally due to topsoil erosion.
Desertification feedback loops
In drylands, erosion removes vegetation cover and productive topsoil, increasing risks for runoff, wind erosion, and drought. This can initiate reinforcing feedback loops converting productive lands into deserts through desertification.
Effects of topsoil loss on flooding and runoff
Topsoil erosion also elevates risks for destructive flooding events and excess nutrient runoff. Vegetation removal and soil compaction reduce the landscape’s ability to absorb rainfall.
Reduced rainfall infiltration
Healthy topsoil acts like a sponge, absorbing and slowly infiltrating rainfall. After erosion, compacted subsoils with less porous structure prevent rapid water infiltration. More rainfall becomes overland flow.
Increased surface runoff
Bare, depleted soils have much higher runoff potential compared to vegetated, high-organic matter soils. This also increases downslope erosion until the underlying strata is exposed.
Faster streamflow response
In watersheds with substantial erosion damage, streams rise faster during storms as rainfall rapidly runs off denuded hillsides. Streams also can’t recharge groundwater as effectively.
Higher flooding risks
With reduced rainfall infiltration and absorption capacity, eroded landscapes have greatly elevated flood hazards. Sudden high volumes of runoff rapidly swell streams and inundate floodplains.
Best management practices to reduce topsoil erosion
Sustainable land management is key to reducing detrimental topsoil erosion. Agricultural practices play a major role, but urban development and forestry methods also impact erosion rates. Some important best management practices include:
Conservation tillage
Conservation tillage systems like no-till farming reduce soil disturbance and leave ample crop residue cover to protect topsoil from water and wind erosion. This boosts organic matter levels over time.
Cover crops
Planting cereal rye, clover, and other cover crops provides living roots in the ground and protective cover when cash crops aren’t growing. The added organic matter also improves soil structure.
Crop rotations
Rotating through different cash crops and cover crops breaks pest cycles while increasing soil biodiversity and organic matter. Rotating row crops with forages is ideal.
Contour farming
Tilling, planting, and managing row crop operations across the contour lines on slopes protects soils during heavy rains. Contour buffer strips further reduce sheet erosion between rows.
Terracing
On steep slopes, terraces serve as leveled steps that intercept erosive surface flows and raise infiltration. Terraces reduce slope length to limit rapid runoff.
Perennial crops
Perennial grains, fruits, and forage crops protect soils year-round with continuous living roots and soil cover. Diverse native perennial prairie plants are ideal.
Tree buffers and windbreaks
Linear rows of trees or shrubs planted along field edges or around crops reduce wind speed across fields. The anchored roots also filter out sediments from runoff.
Mulching
Applying organic mulch or plastic films atop soils protects the surface from raindrop impacts while reducing evaporation and runoff. Mulching is useful on croplands and disturbed areas.
Watershed soil conservation
At the watershed scale, soil conservation efforts must integrate across agricultural operations, urban lands, and forested habitats. Collaborative planning helps coordinate erosion control practices.
What happens if topsoil erosion continues unchecked?
If current land mismanagement persists leading to ongoing topsoil erosion losses, the future impacts could be quite severe for agriculture and the environment. Here are some potential consequences if erosion rates are not slowed:
Further declines in crop yields
World population is projected to reach 9.7 billion people by 2050. Feeding this population will require raising worldwide food production by 50%. However, accelerating topsoil erosion poses a major threat to meeting this target if poor soil conservation causes yields to fall further.
Loss of farmlands from desertification
Ongoing erosion of vulnerable dryland soils could bring over 500 million hectares of cultivated land worldwide into a cycle of degradation and desertification by 2050. The livelihoods of nearly 1 billion people who inhabit these lands would be jeopardized.
Rising food costs and insecurity
With productive farmland shrinking due to erosion, future food supplies will dwindle leading to higher market prices and increasing food insecurity. Vulnerable populations will experience malnutrition and social unrest.
Extinctions from loss of soil biodiversity
The immense diversity of organisms living in soils provide vital ecosystem services. Yet soil biodiversity remains poorly studied. Further erosion-driven losses of species and genetic diversity could irreversibly upset belowground food webs.
Intensified climate change
Topsoil erosion liberates around 75 billion tons of carbon globally each year, adding to atmospheric CO2. With accelerated erosion, this process would intensify, constituting a positive feedback to climate change.
Collapse of natural ecosystems
Beyond farm fields, erosion of soils supporting forests, prairies, wetlands, and other native ecosystems could trigger disastrous declines in biodiversity and species extinctions around the world.
Conclusion
In summary, excessive topsoil erosion poses grave threats to global food security, water quality, ecosystem health, and the climate. The rich organic matter and fertility topsoil provides are essential for agricultural productivity and environmental quality. But human land mismanagement has stripped and degraded soils throughout history, and erosion continues today far faster than new soil formation. The resulting declines in soil quality, crop yields, and ecosystem services highlight why reversing topsoil loss is absolutely vital for a sustainable future. With a growing population and warming climate stressing ecosystems, now is the time to invest heavily in regenerative agricultural practices, cover cropping, holistic grazing, conservation tillage, erosion control infrastructure, and other essential soil conservation strategies before this precious resource slips away.
