What is soil degradation?

What is soil degradation?	LC0063
David Cummings, Melbourne December, 1999

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Soil degradation occurs where our activities (either directly or indirectly) cause it to become less vigorous or less healthy. The ultimate degradation is the removal or loss of its physical components.

Acidification, salinity, organic depletion, compaction, nutrient depletion, chemical contamination, landslides, and erosion are all forms of soil degradation that can be brought about by inappropriate land use practices.

But what is an inappropriate land use practice? The answer is very much dependant on the robustness of the land and its climate. Soil degradation results if we push production to levels beyond the ability of land to support it. If production is carefully matched to the robustness of the land (land capability), then we have sustainable land use.

Soil degradation is undesirable. It results in our land being less useful and less productive. The soil becomes less able to support plant and animal growth as there is a decline in levels of available moisture, available nutrients, and biological activity.

As soil degradation develops, land can become unsuitable for particular uses. In extreme cases it can stop nearly all plant growth (eg salt pans and areas of severe sheet erosion). In less extreme (and less visible) cases it will restrict production (eg compaction reducing plant growth and grain yields). It may even prohibit specific activities (eg acidification preventing sub-clover growth).

Perhaps we should remember that the collapse of the Mesopotamian and the Roman Empires is often blamed on degradation of their grain growing soils.

A soil can degrade in 3 ways:

Physical, chemical or biological run-down causing a reduction in vigour. This can result from excessive product removal (depleting soil nutrients), reduction in plant growth, lowered organic cycling, increasing soil temperatures, leaching, compaction and surface crusting.
Reduction in mass and volume through erosion. This reduces the physical size of the soil ecosystem.
Accumulation of specific soil chemicals to levels that detrimentally effect plant growth. Such materials include: soluble salts (causing salinity); hydrogen ions (causing acidification); and, some chemicals from industrial, mining and agricultural activities (chemical contamination).

The underlying table presents more specific information on the major forms of degradation, how they effect our environment, and what land management practices can help to contain and control them.

Implementation of better land management practices is strongly influenced by economic pressures and social pressures. It is important that our economic and social systems acknowledge the need to maintain and enhance our soil. Soil should never be regarded as an unlimited and indestructible resource. Soil is not a commodity. Soil should be our partner in production.

Clearly soil degradation is not just a problem for our time. A lot of it is inherited from past activities. Further, anything we do now will consequentially effect future generations. We must avoid compromising future land use potential. We need to learn from the past, apply current solutions and protect the future.

Forms of soil degradation

Forms	Definition	Consequences	Control of causes
Sheet and Rill Erosion	Rain drops and surface flows causing shallow stripping of soil.	Results in loss of the most productive part of the soil profile . Reduced plant growth. Deposition of eroded material frequently causes damage. Catchment water quality, stream habitat and water storages affected.	A good vegetative cover over catchment lands is essential. Minimize cultivation and land disturbance. Maintain strong cycling of organic materials by having vigorously growing vegetation.
Gully Erosion	Concentrated flows of water scouring along flow routes causing sharp sided entrenched channels deeper than 0.5 m	Land is physically dissected, limiting access. Excess draining and drying of depressions. Damage to roads and other public utilities.	Reduce runoff from catchment lands using the same methods as outlined for sheet and rill erosion.
Tunnel Erosion	Scouring of pipes and tunnels through susceptible subsoils because of excessive quantities of water moving through the soil and concentrating along cracks, root channels and animal burrows.	Physical disruption of soil. Loss of productive capacity. Deposition of inhospitable soil material on lower lying lands. Dispersed clay material readily moves to streams.	Develop and maintain strong vegetative cover to increase plant water use. May need soil conditioners to decrease susceptibility of soil in bad areas.
Wind Erosion	Where wind has direct access to bare dry soil and causes soil detachment and removal. Fine material can be transported long distances. Coarser material moves only locally by bouncing and rolling.	Dust days affecting aircraft, environment and clothes washing. Loss of nutrients from topsoil in dust. Accumulation of sand on roads, railway lines and water supply channels.	Reduce the amount of soil bared through reduced cultivation, stubble retention, minimization of stock damage to vegetation and soil surfaces. Maximize organic matter on the soil surface through strategic crop rotations and grazing management.
Coastal Dune Erosion	Reactivation of sand movement because of loss of surface cover through uncontrolled and/or excessive recreational activity.	Loss of coastal amenity and damage to adjacent areas due to sand drift.	Careful retention of vegetation in sensitive areas. Restriction of foot and vehicular traffic on sensitive areas.
Land Slips	Where sloping soils become unstable and slip downhill. Usually brought about by increase in soil mass because of excess moisture in the soil. Can also result from construction activities.	Causes damage to private and public assets, restricts access and can add sediment loads to streams.	Minimize adverse changes to soil hydrology in susceptible areas. Minimization of physical disturbance. Stabilization of slippage areas using vegetation and physical structures.
Stream Bank Erosion	Where streams begin cutting deeper and wider channels as a consequence of increased peak flows or the removal of local protecting vegetation.	Increase in stream sediment and suspended material. Loss of stream habitat values.	Manage stream flows as much as possible through broadscale catchment management practices. Manage stream frontage areas to retain adequate vegetation. Minimize need for direct animal access for watering.
Dryland Salinity	Where saline groundwater rises towards soil surface and interferes with plant growth. Primarily due to interference with hydrologic cycle.	Loss of productivity from land with surface close to saline groundwater surfaces. Contamination of surface flows of water. Loss of stream and wetlands habitat.	Increase the vigor and plant water use in catchment to groundwater systems.
Acidification	Where the acid level of soil progressively increases and interferes with plant growth. Associated with nitrate leaching, product removal and fertilizer practice.	Reduce plant production. Problems with rhizome nodulation of sub-clovers. Acidification of streams.	Use deep rooted species to maximize nutrient and water cycling in the plant root zone. Liming.
Soil Compaction	Where productivity of soil is reduced because of physical changes to the nature of soil. Frequently associated with surface crusting, plough pans, dispersive clays, excessive cultivation and stock trampling.	Poor water and air movement in and through soils causing a lowering of biological activity.	Reduced mechanical disturbance via cultivation and trafficking. Careful selection of cropping/ley rotations. Maximize organic cycling to maximize biological activity.

Further information
Chisholm A. and Dumsday R. (Eds.) (1987) Land Degradation: problems and policies. Cambridge University Press
McTainsh G. and Boughton W.C. (Eds.) (1993) Land Degradation Processes in Australia. Longman Cheshire.

This note replaces note number SC0005.

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

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