2 - Soil threats
The process in which the concentration of hydrogen ions in the soil gradually increases, caused by removal of (slightly alkaline) crop produce, leaching and the use of acidifying N fertilizer types, accelerated or insufficiently compensated by the natural constituents of a soil among which the parent material.
The process in which relatively dry land becomes increasingly arid, typically losing its bodies of water as well as vegetation and wildlife either directly via climate change or indirectly via soil degradation resulting from poor management.
The wearing away of the land surface by water, wind, ice, gravity or other natural or anthropogenic agents that abrade, detach and remove soil particles or rock material from one point on the earth’s surface, for deposition elsewhere, including gravitational creep and so-called tillage erosion.
The gradual depletion of reserves of nutrients and organic matter in soils.
Accumulation of agents able to promote biological stress and subsequent loss of yield such as nematodes, weeds, microorganisms, mice, etcetera, favoured by, for instance, a too narrow crop rotation.
Increase of settlement areas over time. This process includes the development of scattered settlements in rural areas, the expansion of urban areas around an urban nucleus (including urban sprawl), and the conversion of land within an urban area (densification).
Organic matter loss
Decline of organic matter content in one or more soil layers when the annual loss of organic matter (e.g. due to oxidation or erosion) is insufficiently compensated for by the annual gain of organic matter, resulting from crop residues, composts and manures.
Accumulation of soluble salts (more soluble than gypsum) in the upper soil layers (saline soil = soil containing enough soluble salts to negatively affect most crop plants, commonly 4000 μS m-1).
Increase in the amount of exchangeable Na of a soil (sodic soil = soil containing enough Na to negatively affect most crop plants by changing the physical soil properties).
Changing the nature of the soil such that there is a decrease in the volume of voids between soil particles or aggregates; it is manifested as an increase in bulk density and a severely compacted soil can become significantly less permeable and less aerated. Manmade compaction is caused by poaching (trampling of animal hooves repeatedly) or by the passage of heavy machinery. Other typical examples are “plough pans” (plough sole or traffic pan) which can be formed due to tillage and which can negatively affect root development and drainage.
Accumulation of nutrients, metals or organic compounds leading to a reduction of the capacity of soils to deliver soil functions. Contamination may have a direct toxic effect on the plants, animals or humans living in, on, or from that soil, or have an indirect toxic effect due to accumulation in the whole trophic chain.
The process of covering of a soil by buildings, or types of artificial material which may be very slowly permeable to water (e.g. asphalt or concrete). Soil sealing can cause rapid overland flow after precipitation where water cannot soak away leading to potential flooding. A soil is unable to function effectively when sealed.