What Soil Degradation Is, What Causes It and Why It Matters

Key takeaways

• Soil degradation is a loss of function: a soil that grows less, holds less water, resists erosion less well or supports fewer living things, and does not recover by itself on a useful timescale.
• It has physical, chemical and biological forms, and in the field they feed each other.
• Soil is hard to replace, because it forms over spans far longer than a lifetime and can be lost in a single season.
• Degradation rarely has one cause: it appears where natural vulnerability meets human pressure such as clearing, overgrazing, tillage, irrigation, sealing and mining.
• Its effects reach beyond the farm, to food supply, water quality, climate and rural economies.

Soil is a living system, not just dirt

Most people picture soil as a passive layer that plants happen to stand in. In reality it is a layered, living material built from weathered rock, decomposing organic matter, water, air and an enormous community of organisms. Fungi, bacteria, worms, insects and microscopic animals all take part in turning dead plant material into nutrients that roots can absorb. The result is a structure full of tiny pores and crumbs that holds water, lets air move and gives roots something to grip.

Soil degradation is the decline of that system's ability to do its jobs. A degraded soil may grow less, hold less water, resist erosion less well, or support fewer living things. It can happen quickly, as when a heavy storm strips a bare field, or so slowly that nobody notices until yields fall or a stream turns brown after every rain.

What does degradation actually mean?

Scientists use the word to describe a loss of function, not simply a change. FAO's soils portal defines soil degradation as a change in soil health status that diminishes the capacity of the ecosystem, so that degraded soils no longer provide the normal goods and services of that soil. Soil changes constantly through seasons, crops and weather, and that is normal. Degradation is a change that reduces what the soil can provide to people and ecosystems, and that does not reverse by itself on a useful timescale. It is usually described in terms of several overlapping processes:

• Physical degradation: erosion, compaction, crusting and the breakdown of soil structure.
• Chemical degradation: salt build-up, acidification, nutrient depletion and contamination.
• Biological degradation: loss of organic matter and a shrinking, simplified community of soil organisms.

These categories are convenient, but in the field they feed each other. A soil that loses organic matter becomes less stable, so it erodes more easily, so it loses the richest topsoil, so plants grow worse and return even less organic material. Many degraded landscapes are stuck in exactly this kind of downward loop.

Why is soil so hard to replace?

The key problem is time. Soil forms from rock and organic material over spans that dwarf a human lifetime, while it can be lost in a single season of careless management. The UN Convention to Combat Desertification states that current farming practices erode soils up to 100 times faster than natural processes replenish them. For practical purposes, a farmer or gardener should treat the soil they have as a finite inheritance. Compost, mulch and good practice can rebuild fertility and structure over years, but rebuilding is far slower and costlier than protecting what is already there.

Another difficulty is that damage often hides. Fertiliser can mask falling natural fertility for a while. Irrigation can mask a water-holding problem. A green crop can stand on soil whose structure is quietly collapsing. By the time the symptoms are obvious, the underlying decline may be well advanced.

The functions at stake

Healthy soil quietly performs services that society relies on every day:

• Growing food, fibre and timber.
• Absorbing rainfall and releasing it slowly, which reduces flooding and sustains streams between storms.
• Filtering and buffering water so that pollutants are held or broken down before they reach groundwater.
• Storing carbon in organic form, which links soil management to climate.
• Providing habitat for a huge share of the planet's biodiversity.
• Supporting buildings, roads and gardens by providing a stable base.

When degradation weakens these functions, the costs spread outward: muddier rivers, clogged reservoirs, dustier air, lower farm resilience and more pressure to clear new land.

Where does soil degradation show up?

Degradation is not confined to any single climate or farming system. Dry regions suffer wind erosion and salt build-up. Wet and hilly regions suffer gullies and landslides. Intensively cropped plains can suffer compaction and organic matter loss. Pastures can be damaged by too many animals on the same ground. Cities seal soil under pavement and bury it under construction fill. Mining and industry leave contaminated ground behind. Even a suburban lawn can be compacted, acidic and starved of organic matter.

At the largest scale, severe degradation in dry regions is called desertification, a term that refers to land losing productive capacity in arid, semi-arid and dry sub-humid areas. It does not mean existing deserts are spreading like a tide. It means working land is being pushed into a barren state by a mix of climate and human pressure.

How is degradation recognised?

Experts look at indicators rather than a single measurement. Common signs include thinner or paler topsoil, exposed subsoil, surface crusts that shed water, ponding after moderate rain, small channels that deepen into gullies, white salt crusts, stunted or patchy crops, and a drop in earthworms and other visible life. Laboratory tests add further evidence, such as organic matter content, acidity, salinity and nutrient levels.

Degradation versus natural variation

Not every poor patch is damage. Some soils are naturally shallow, sandy, stony or salty because of the rock and climate they formed under. Good assessment compares a site with what it could be: a similar soil under good management, or the same place in its earlier condition. Without that comparison it is easy to blame management for what is really native character, or to accept a damaged field as normal because nobody remembers it any other way.

Why does it matter beyond the farm?

It is tempting to treat soil as a farmer's concern, but its condition reaches everyone. The IPBES assessment of land degradation and restoration found that human-caused land degradation undermines the well-being of at least 3.2 billion people and put its cost at about 10% of annual global gross product. Food supply depends on it directly. Water quality depends on it because soil is the first filter between land use and rivers. Climate depends on it because soils hold a large store of carbon that can be released when ground is disturbed or can be built up by good practice. Local economies and rural communities depend on land that stays productive from one generation to the next.

The encouraging side is that much degradation responds to better management. Keeping the ground covered, disturbing it less, returning organic material, matching animal numbers to the land and shaping slopes to slow water are all well understood measures. They are not magic, and results depend on place, but they give a clear direction.

What causes soil degradation

Degradation rarely has one cause. It usually appears where natural vulnerability, such as a steep slope, a dry climate or a fragile soil, meets human pressure. The same practice can be harmless on one site and damaging on another.

Land clearing and deforestation

Forests and woodlands protect soil in many ways: the canopy intercepts rain, litter covers the ground, roots bind soil and open channels for water, and a steady supply of organic material feeds soil life. Removing trees takes all of this away at once. Exposed ground is struck directly by raindrops and wind, litter inputs stop, and organic matter begins to burn away faster than it is replaced. Roads and tracks cut through cleared land are especially damaging because they concentrate runoff.

Overgrazing and trampling

Grazing animals are not the problem by themselves, and well-managed grazing can be compatible with healthy soil. Trouble begins when too many animals stay too long on the same ground or return before plants recover. Vegetation is cropped short, roots shrink, bare patches open up, and hooves compact the surface, particularly when it is wet. Gateways and water points often turn into gullies.

Tillage and cropping systems

Ploughing loosens soil and controls weeds, but it also destroys aggregates, speeds the breakdown of organic matter and leaves the surface bare. Long bare fallows, cultivating up and down slopes, removing all residues and growing the same crop year after year add to the damage. Heavy machinery compacts soil, sometimes well below the cultivated layer.

Irrigation and water management

Irrigation can transform dry land into productive farms, but it is also a leading route to salinization and waterlogging. Water applied without adequate drainage raises the water table and leaves salts behind as it evaporates. Leaking canals can waterlog neighbouring land, and over-extraction of groundwater near coasts can draw seawater inland.

Urban growth, mining and industry

Sealing soil under roads, roofs and car parks removes its ability to absorb water and increases runoff. Construction strips topsoil, mixes and compacts layers and often buries fertile ground under fill. Mining, smelting and waste storage can remove soil entirely or spread contaminants across wide areas.

Climate and social amplifiers

Intense storms, long droughts, strong winds and wildfire all expose or move soil, and changing rainfall patterns may raise risks in some regions. Economic and social factors, such as insecure land tenure, short-term financial pressure and lack of access to advice, often explain why damaging practices persist even when people know better.

Main causes at a glance

Cause	How it harms soil
Land clearing and deforestation	Removes the canopy, litter and roots that protect the surface, so exposed ground is struck by rain and wind and organic matter burns away faster than it is replaced
Overgrazing and trampling	Too many animals on the same ground for too long crop vegetation short, open bare patches and compact the surface
Tillage and cropping systems	Destroys aggregates, speeds the breakdown of organic matter and leaves the surface bare; heavy machinery compacts soil
Irrigation and water management	Without adequate drainage it raises the water table and leaves salts behind as water evaporates
Urban growth, mining and industry	Sealing, stripping and burying soil, and contamination from mining, smelting and waste storage
Climate and social amplifiers	Storms, droughts, wind and wildfire move soil; insecure tenure and short-term pressure keep damaging practices going

Seeing causes in the landscape

A useful habit is to separate the visible symptom, the process behind it and the driver underneath. A gully is a symptom, concentrated runoff is the process, and a compacted track or missing waterway is the driver. Filling the gully while leaving the driver untouched will fail. The assessment guide on this site explains how to walk a site, read vegetation and edges, and find out what the land was used for in the past.

How to use this site

The guides here move from understanding to action. Start with the processes: erosion, compaction, salt, nutrient and organic matter loss, contamination and acidification. Then read about restoration practices with their honest limits, and finally simple ways to observe and assess soil yourself. The glossary explains terms such as horizon, aggregate, infiltration and cation exchange in plain language.

Sources and further reading

• FAO Soils Portal: Soil degradation and restoration: FAO's definitions of soil degradation, land degradation, desertification and soil erosion.
• UNCCD: Land degradation neutrality, overview: the UN Convention to Combat Desertification's statement that current farming practices erode soils up to 100 times faster than natural processes replenish them.
• IPBES: Worsening worldwide land degradation now critical: the media release for the IPBES land degradation and restoration assessment: at least 3.2 billion people affected, a cost of about 10% of annual global gross product, a roughly 8% fall in soil organic carbon over 200 years, and restoration benefits averaging ten times the costs.

Frequently asked questions

Is soil degradation the same as erosion?

No. Erosion is one form of degradation, where soil particles are carried away by water or wind. Degradation also includes compaction, salt build-up, acidification, nutrient and organic matter loss and contamination.

Can degraded soil recover?

Often it can improve, but recovery is usually slow and depends on the type and severity of the damage. Some damage, such as the loss of deep topsoil to erosion, cannot be undone on a human timescale.

Does soil degradation only affect farmland?

No. It also occurs in pastures, forests, gardens, urban sites and industrial land. Its effects, including muddy rivers and flooding, are felt well beyond the land itself.

How do I know if my soil is degraded or just naturally poor?

Compare it with similar soil under good management or with its own earlier condition. Naturally sandy, stony or shallow soils have limits that are not caused by damage.