Soil retrogression and degradation
Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a
According to the Center for Development Research at the University of Bonn and the International Food Policy Research Institute in Washington, the quality of 33% of pastureland, 25% of arable land and 23% of forests has deteriorated globally over the last 30 years. 3.2 billion people are dependent on this land.[3]
General
At the beginning of soil formation, the bare rock outcrops are gradually colonized by
After a certain time of parallel evolution between the ground and the vegetation, a
The cycles of evolution of soils have very variable durations, between tens, hundreds, or thousands of years for quickly evolving soils (A horizon only) to more than a million years for slowly developing soils. The same soil may achieve several successive steady state conditions during its existence, as exhibited by the
Ecological factors influencing soil formation
There are two types of ecological factors influencing the evolution of a soil (through alteration and humification). These two factors are extremely significant to explain the evolution of soils of short development.
- A first type of factor is the average climate of an area and the vegetation which is associated (biome).
- A second type of factor is more local, and is related to the original rock and local drainage. This type of factor explains appearance of specialized associations (ex peat bogs).
Biorhexistasy theory
The destruction of the vegetation implies the destruction of evoluted soils, or a regressive evolution. Cycles of succession-regression of soils follow one another within short intervals of time (human actions) or long intervals of time (climate variations).
The climate role in the deterioration of the rocks and the formation of soils lead to the formulation of the theory of the biorhexistasy.
- In wet climate, the conditions are favorable to the deterioration of the rocks (mostly chemically), the development of the vegetation and the formation of soils; this period favorable to life is called biostasy.
- In dry climate, the rocks exposed are mostly subjected to mechanical disintegration which produces coarse detrital materials: this is referred to as rhexistasy.
Perturbations of the balance of a soil
When the state of balance, characterized by the ecosystem climax is reached, it tends to be maintained stable in the course of time. The vegetation installed on the ground provides the humus and ensures the ascending circulation of the matters. It protects the ground from erosion by playing the role of barrier (for example, protection from water and wind). Plants can also reduce erosion by binding the particles of the ground to their roots.
A disturbance of climax will cause retrogression, but often, secondary succession will start to guide the evolution of the system after that disturbance. Secondary succession is much faster than primary because the soil is already formed, although deteriorated and needing restoration as well.
However, when a significant destruction of the vegetation takes place (of natural origin such as an avalanche or human origin), the disturbance undergone by the ecosystem is too important. In this latter case, erosion is responsible for the destruction of the upper horizons of the ground, and is at the origin of a phenomenon of reversion to pioneer conditions. The phenomenon is called retrogression and can be partial or total (in this case, nothing remains beside bare rock). For example, the clearing of an inclined ground, subjected to violent rains, can lead to the complete destruction of the soil. Man can deeply modify the evolution of the soils by direct and brutal action, such as clearing, abusive cuts, forest pasture, litters raking. The climax vegetation is gradually replaced and the soil modified (example: replacement of leafy tree forests by moors or pines plantations). Retrogression is often related to very old human practices.
Influence of human activity
Erosion can be influenced by human activity. For example,
- Overgrazing of animals
- Monoculture planting
- Row cropping
- plowing
- Crop removal
- Land-use conversion
Consequences of soil regression and degradation
Here are a few of the consequences of soil regression and degradation:
- soil degradation already do not have.[8] Slight degradation refers to land where yield potential has been reduced by 10%, moderate degradation refers to a yield decrease from 10 to 50%. Severely degraded soils have lost more than 50% of their potential. Most severely degraded soils are located in developing countries. In Africa, yield reduction is between 2 and 40%, with an average loss of 8.2% of the continent.[8]
- soil degradationcan cause floods.
- Deterioration of the heavy metals). The run-off with pesticides and fertilizers make water quality dangerous. The ecological impact of agricultural inputs (such as weed killer) is known but difficult to evaluate because of the multiplicity of the products and their broad spectrum of action.
- Biological diversity: soil degradation may involve perturbation of microbial communities, disappearance of the climax vegetation and decrease in animal habitat, thus leading to a biodiversity loss and animal extinction.[9]
- Economic loss: the estimated costs for land degradation are US$44 billion per year. Globally, the annual loss of 76 billion tons of soil costs the world about US$400 billion per year. In Canada, on-farm effects of land degradation were estimated to range from US$700 to US$915 million in 1984. The economic impact of land degradation is extremely severe in densely populated South Asia, and sub-Saharan Africa.[8]
Soil enhancement, rebuilding, and regeneration
Problems of soil erosion can be fought, and certain practices can lead to soil enhancement and rebuilding. Even though simple, methods for reducing erosion are often not chosen because these practices outweigh the short-term benefits. Rebuilding is especially possible through the improvement of soil structure, addition of organic matter and limitation of runoff. However, these techniques will never totally succeed to restore a soil (and the fauna and flora associated to it) that took more than a 1000 years to build up. Soil regeneration is the reformation of degraded soil through biological, chemical, and or physical processes.[2]
When productivity declined in the low-clay soils of northern Thailand, farmers initially responded by adding organic matter from
In 2008, three years after the initial trials,
See also
- Soil § Degradation
- Acid sulfate soil
- Alkaline soil
- Hardpan
- Land degradation
- Environmental impact of irrigation
- Land reclamation
- Land improvement
- Planetary boundaries
- Plant growth
- Soil biodiversity
- Soil nutrient
References
- .
- ^ a b Johnson, D.L., S.H. Ambrose, T.J. Bassett, M.L. Bowen, D.E. Crummey, J.S. Isaacson, D.N. Johnson, P. Lamb, M. Saul, and A.E. Winter-Nelson. 1997. Meanings of environmental terms. Journal of Environmental Quality 26: 581-589.
- ISBN 978-3-86581-838-6.
- ^ "Plant Production and Protection Division: How is soil formed?". www.fao.org. Retrieved 2020-03-09.
- ^ "Succession: A Closer Look | Learn Science at Scitable". www.nature.com. Retrieved 2020-03-09.
- ^ "Why soil is disappearing from farms". www.bbc.com. Retrieved 2020-03-09.
- ^ FAO Database, 2003
- ^ a b c ESWARA, H. "Land Degradation: An overview". USDA. Retrieved 3 November 2020.
- ^ Sims, G. K. 1989. Biological degradation of soils. Advances in Soil Science. 11:285-326.
- IWMI