Soil degradation

Degradation of biological soil quality

Decline in organic matter

Soil organic matter includes (PDF) both living organisms and the remains of dead organisms such as plant residues, manure and compost. Its content is influenced by climate, soil texture, hydrology, water management, land use and vegetation, and varies in the Netherlands depending on soil type and crops. Soil organic matter is essential for soil functioning, including water regulation, nutrient balance and carbon storage.

A decline in organic matter can result from accelerated decomposition due to natural or human influences such as ploughing, from reduced input of organic matter, for example due to soil sealing, or from lowering water tables, which speeds up the breakdown of organic matter and can lead to subsidence or compaction. Organic matter content and soil biodiversity are closely linked: fewer organisms in the soil mean less organic matter is produced and cycled, while a decline in organic matter in turn reduces the food source available to soil organisms. A decline in organic matter reduces the soil’s capacity to retain water and nutrients, making it more sensitive to drought, compaction and erosion.

Biodiversity decline

Biodiversity is a core component of biological soil quality (PDF). Bacteria and fungi break down organic matter and are themselves eaten by small organisms, releasing nutrients such as nitrogen and phosphate for plants to absorb. These organisms are in turn eaten by others, releasing nutrients again. Fungi break this organic matter down more slowly than bacteria, which gives organisms more time to absorb the released nutrients. A healthy fungi-to-bacteria ratio helps soil resist disease, pests, and weather extremes. Intensified land use disrupts this system: it reduces soil biodiversity, food web complexity, and the biomass of most soil organism groups, and shifts the fungi-to-bacteria balance toward bacteria. When this happens (PDF), organic matter breaks down too fast, nutrients leach out before they can be absorbed, and species interactions decline, reducing the soil's biological quality. Soil biology and soil health are also directly linked to human health; a healthy soil with high biodiversity has a lower risk of pathogens and pests.

Degradation of chemical soil quality

Soil contamination

Soil contamination in the Netherlands includes point and diffuse contamination. Point contamination can be caused by former land uses, such as industrial spills. Diffuse contamination includes former uses (such as diffuse lead in urban areas), deposition through air or water (floods), and agricultural pesticides and industrial chemicals. Emerging contaminants, such as per- and polyfluoroalkyl substances (PFAS), add to these challenges, as effective remediation techniques and legal frameworks are not always available. Soils naturally supply nutrients such as nitrogen, phosphorus and potassium. In agricultural soils (PDF), these nutrients are also added through mineral fertilisers and animal manure to replace nutrients removed through crop production. Over many years, deposition of nitrogen and sulphur compounds has disturbed soil chemistry, leading to an oversupply of certain nutrients relative to others and disrupting nutrient balance. This is called eutrophication and can alter vegetation and biodiversity. Soil contamination affects (ground)water quality, biodiversity, and vegetation, and can pose ecological and human health risks depending on the contaminant and its potential spread. Remediation can also affect soil health, for example when contaminated soil is excavated or treated.

Soil salinisation

Soil salinisation (PDF) occurs when salt enters the soil. This can happen through saline intrusion from seawater and rising saline groundwater, for example due to groundwater extraction. Road salting on infrastructure in winter can also contribute to soil salinisation. Salinisation alters both soil and water conditions: increased salt concentrations interfere with nutrient uptake by plants and affect the metabolism of soil organisms, reducing soil fertility beyond a certain point. As salinity increases, deeper soil layers can become less permeable, limiting agricultural use, while salt-tolerant vegetation may become more prevalent.

Soil acidification

Soil acidification happens when the soil becomes more acidic, measured by a drop in the soil pH (a measure of how acidic or alkaline the soil is). Some soils are naturally more acid, such as coniferous forests and peat soils. Soil chemistry in forests and nature areas is strongly influenced by atmospheric deposition (PDF) by human activities. Deposition of sulphur and nitrogen compounds contribute to soil acidification and nutrient enrichment. Acidification reduces the soil’s buffering capacity and is associated with changes in vegetation composition and, in many cases, a decline in diversity. This can make soils more sensitive to drought, diseases and pests.

Degradation of physical soil quality

Soil compaction

Soil compaction occurs when heavy pressure is applied to the soil (PDF), causing the soil structure to deform and pore spaces to collapse. This reduces porosity and permeability, making it more difficult for air and water to move through the soil and limiting the availability of oxygen and water for plant roots and soil life. Compaction is particularly associated with the use of heavy machinery in agriculture and forestry, which causes subsoil compaction, but can also result from infrastructure and buildings covering and pressing on the soil. Topsoil compaction is a different type, which can occur in nature areas and parks with heavy foot and vehicle traffic, or through heavy rainfall on bare land. As a result of compaction (PDF), root growth is restricted and the soil’s capacity to infiltrate, store and drain water is reduced. This can lead to increased surface runoff, waterlogging, and greater sensitivity to soil erosion. Soil compaction can also trigger or accelerate other soil degradation processes. Excavation and earthmoving also disturb the soil and affect soil biology, for example when topsoil is stripped and stored.

Soil sealing

Soil sealing is the covering of the soil surface with impervious materials such as concrete, metal, glass and plastic, which make the soil impermeable. It is a direct cause of land take, the process in which (semi-)natural land is converted into artificial land, for example for the construction of urban areas and infrastructure. In urban areas, sealing often continues below the surface: buildings, paving, pipes and cables place sustained pressure on the subsoil, a form of underground congestion. A sealed soil can no longer function as a living soil. Water can no longer infiltrate, and the soil loses resources such as nutrients and moisture. This reduces agricultural productivity, carbon storage and biodiversity, and increases the risk of heat stress, flooding, and runoff, while reducing groundwater storage.

Soil erosion

Soil erosion is the process in which individual soil particles are detached and redistributed to another location, driven by water and wind. This process washes out or blows away organic matter and nutrients. For more information on soil erosion, visit the soil erosion page.

Floods & drought

Pluvial flooding, caused by heavy rainfall rather than overflowing rivers or seas, can wash away soil nutrients and change the soil's chemistry through standing water. Other forms of soil degradation increase surface runoff, which worsens the impact of flooding on the soil. Drought reduces soil moisture and water availability, which limits plant health and decreases overall vegetation productivity. As a result, the topsoil is more exposed to erosion during strong winds. It also changes the soil's structure, reducing its ability to infiltrate rainwater and accelerating evaporation. For more information, visit the pages on pluvial flooding and drought.

Agriculture

Soil degradation directly affects agricultural production in the Netherlands (PDF) by reducing soil quality and making crop production less stable. Compaction and loss of organic carbon make soils more vulnerable to extreme weather, pests and diseases, leading to lower and less stable crop yields. Dutch agricultural soils also show increasing deficiencies in essential micronutrients (PDF), alongside the presence of harmful substances, which together reduce the nutritional value of food for consumers. In some parts of the Netherlands, salinisation of the soil further threatens agricultural production. Over time, declining nutrient availability reduces the soil's capacity to sustain long-term production, resulting in smaller harvests.

Water management and supplies

Healthy soils play a key role in water management by absorbing and storing water during wet periods and gradually releasing it during dry periods. This sponge function helps limit flooding in wet conditions and reduces drought impacts during dry spells. When soil organic matter declines (PDF), or the soil structure is affected (compaction), infiltration capacity decreases, leading to increased runoff and erosion. This may also affect the water supplies in the long term.

Soil degradation also affects water quality (PDF). A healthy soil not only helps infiltrate and replenish groundwater, but also filters it. Contamination can affect groundwater supplies. Decomposition processes involving nitrate in groundwater can increase concentrations of heavy metals, sulphate and water hardness, which may result in drinking water quality standards being exceeded. A decline in soil organic matter and soil life can decline the cleaning capacity of the soil.

Nature

In nature and forestry areas, soil degradation reduces the soil’s capacity to regulate nutrients, store and infiltrate water, and sequester carbon. Soil life forms the foundation of the food pyramid. When soil biodiversity declines, these processes are disrupted (PDF), with consequences for above-ground biodiversity and ecosystem functioning. Changes in soil and water conditions can also alter the composition and ecological value of ecosystems, for example through eutrophication.

Built-up areas

In built-up areas, the soil itself is degraded through several of the processes described before. Soil sealing covers the surface with impervious materials, cutting off infiltration and the exchange of nutrients and moisture. Underground congestion adds to this: buildings, paving, pipes and cables place sustained pressure on the subsoil, restricting the space available for water, air and soil life and affecting groundwater flow and seepage pressure. Contamination is also common in cities, both from current activity and from historical land use, such as industrial spills and diffuse lead deposits.

Soil degradation, in turn, affects the built environment as well. Sealed soils infiltrate less rainwater, increasing surface runoff and, with it, the risk of flooding for streets, buildings and infrastructure. A decline in organic matter and lowering water tables can lead to subsidence, which poses risks to building foundations, roads, pipes and cables. As the area of healthy, unsealed soil in built-up areas shrinks, so does the soil's capacity to buffer heavy rainfall and store water during droughts, capacity cities increasingly need as the climate changes.