Soil guide
Soil Degradation
Soil degradation, term by term
Guides, terms and answers about how soil degrades, in plain language.
Plate I
Terms
The terms, one by one
Each card states what its record says: its name and a line of its own text.
-
-
- Soil horizonA soil horizon is a distinct layer in a soil profile, set apart from the layers above and below by colour, texture, structure or composition. Horiz...Open the plate
- Soil profileA soil profile is the vertical section from the surface down to the underlying parent material, showing all of its horizons in order. Digging a pit...Open the plate
- Parent materialParent material is the rock or sediment from which a soil develops through weathering. It strongly influences texture, mineral content and natural ...Open the plate
- HumusHumus is the dark, stable fraction of organic matter that remains after most plant and animal residues have decomposed. It binds mineral particles ...Open the plate
- Soil organic matterSoil organic matter is all the living and dead organic material in soil, from fresh residues and roots to stable humus. It underpins structure, nut...Open the plate
- AggregateAn aggregate is a small crumb of soil particles held together by organic matter, fungal threads, roots and minerals. Stable aggregates create the p...Open the plate
- Soil structureSoil structure is the arrangement of soil particles into aggregates and the pores between them. Good structure lets roots, water and air move freel...Open the plate
- Soil textureSoil texture is the relative proportions of sand, silt and clay in a soil. It affects drainage, water holding, nutrient retention and how easily th...Open the plate
- InfiltrationInfiltration is the process by which water enters the soil surface. Crusting, compaction and bare ground reduce it, which increases runoff and eros...Open the plate
- RunoffRunoff is water that flows over the land surface instead of soaking in. It can carry soil, nutrients and pollutants into streams and drains, which ...Open the plate
Guides
Read on
Longer, plain-language guides that put the plates and the terms in context.
- What Soil Degradation Is, What Causes It and Why It MattersSoil degradation is the decline of soil's ability to grow plants, hold water and cycle nutrients. Learn what drives it and why it matters beyond the farm.
- Soil Erosion by Water and Wind: Mechanisms and Warning SignsHow water and wind detach and carry soil away, the forms erosion takes from sheet to gully, and the field signs that tell you it is happening.
- Soil Compaction and the Loss of Soil StructureWhy compacted, crusted soil sheds water and starves roots, how structure forms and collapses, and the field signs and causes of compaction.
- Salinization and Sodicity: When Salt Takes Over the SoilHow salts accumulate in soil, how salinity differs from sodicity, why irrigation and shallow water tables matter, and how to recognise the signs.
- Nutrient Depletion, Organic Matter Loss and the Decline of Soil LifeWhy soils run down when crops remove more than is returned, how organic matter and soil biology decline together, and what the warning signs look like.
- Soil Contamination and Acidification ExplainedHow pollutants and falling pH damage soil, where they come from, why some contaminants persist, and what testing and management can and cannot do.
What exactly is soil degradation?
Soil degradation is a decline in the soil's ability to support plants, store and filter water, cycle nutrients and shelter living organisms. FAO's soils portal describes it as a change in soil health that diminishes the capacity of the ecosystem to provide its normal goods and services. It can involve physical damage such as erosion and compaction, chemical change such as salt build-up or acidification, or loss of organic matter and soil life, and often all three happen together.
Is soil degradation the same as desertification?
No, they are related but not identical. Soil degradation can occur anywhere, while desertification refers to land degradation in dry regions, where it results from a mix of climate variation and human pressure. FAO's soils portal describes it as land degradation in dryland areas, or a change so severe that the land can no longer be recovered for its original use. Degraded soil is one of the main ingredients of desertification, but a degraded garden in a wet climate is not desertified.
How long does it take for soil to form?
Very long by human standards: soil forms through the weathering of rock and the slow addition of organic material. FAO notes that soil formation and regeneration processes are predominantly slow, so soil lost to erosion or burial should be treated as irreplaceable within a lifetime. The UN Convention to Combat Desertification says current farming practices erode soils up to 100 times faster than natural processes replenish them. Fertility and structure, however, can be improved much faster than a whole soil can form.
What is topsoil and why does losing it matter?
Topsoil is the upper layer of the soil profile, richer in organic matter, biological activity and nutrients than the layers beneath. It is where most roots feed and where most rain is absorbed, so it is the most productive layer and the first one erosion removes. When it is lost, plants have a harder time, the remaining subsoil is denser and less fertile, and the exposed ground erodes more easily. Pale patches on slopes are a typical sign that it has gone.
Can degraded soil really be restored?
Many degraded soils improve substantially with consistent management, especially their structure, organic matter and biology, but recovery is usually slow and uneven. FAO notes that soil regeneration processes are predominantly slow. Some losses, such as deep topsoil removed by erosion or heavy contamination, may be impossible or very costly to reverse on a human timescale. The earlier a problem is caught, the better the outlook, and prevention is cheaper than cure.
Does using fertiliser prevent soil degradation?
No. Fertiliser supplies nutrients but does not protect against erosion, compaction, salinity or loss of organic matter. It can even hide declining fertility by keeping yields up while the soil itself runs down, so a farm can look productive and still depend on constant inputs. Overuse can also acidify soil and pollute water. Fertiliser works best alongside practices that keep soil covered, structured and rich in organic matter, with applications guided by soil testing.
What is the difference between erosion and compaction?
Erosion is the removal of soil particles by water or wind, while compaction squeezes the soil so that its pore space collapses. Erosion takes soil away; compaction leaves it in place but makes it dense, hard and poorly draining. FAO links compaction to livestock concentrated around water points and to heavy machinery and inappropriate tillage. Both can occur on the same land and worsen each other, because compacted ground sheds water, which then runs off and erodes.
Why are white crusts on the ground a warning sign?
A white crust often means dissolved salts have been left behind as water evaporated from the surface. High salt levels make it hard for plants to take up water, so crops can wilt even in damp soil. Crusts typically show in low spots or along the edges of wet patches, and they are often linked to poorly drained irrigation. A laboratory test of the soil can confirm whether the problem is salinity, sodicity or something else, because the remedies differ.