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Overgrazing is the grazing Of natural pastures at stocking intensities above the livestock carrying capacity; the resulting decrease in the vegetation cover is a leading cause of wind and water erosion. It is a significant factor in Afghanistan. Agricultural activities that can cause land degradation include shifting cultivation without adequate fallow periods, absence of soil conservation measures, fertilizer use, and a host of possible problems arising from faulty planning or management of irrigation. They are a major factor in Sir Lankan and the dominant one in Bangladesh. The role of population factors in land degradation processes obviously occurs in the context of the underlying causes.

In the region, in fact, it is indeed one of the two along with land shortage, and land shortage itself ultimately is a ensconce of continued population growth in the face of the finiteness of land resources. In the context of land shortage the growing population pressure, during 1980-1990, has led to decreases in the already small areas of agricultural land per person in six out of eight countries (14% for India and 22% for Pakistan). Population pressure also operates through other mechanisms. Improper agricultural practices, for instance, occur only under constraints such as the saturation of good lands under population pressure which leads settlers to cultivate too shallow or too steep soils, plough fallow and before it has recovered its fertility, or attempt to obtain multiple crops by irrigating unsuitable soils.

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Severe land degradation affects a significant portion of the Earth’s arable lands, decreasing the wealth and economic development of nations. As the land resource base becomes less productive, food security is compromised and competition for dwindling resources increases, the seeds of famine and potential conflict are sewn. [edit] Climate change Significant land degradation from seawater inundation, particularly in river deltas and on low-lying islands, is a potential hazard that was identified in a 007 EPIC report. [citation needed] As a result of sea-level rise from climate change, salinity levels can reach levels where agriculture becomes impossible in very low lying areas.

Soil retrogression and degradation Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to erosion and corresponds to a phenomenon where succession reverts back to pioneer conditions (such as bare ground). Degradation is an evolution, different from natural evolution, related to the local climate and vegetation. It is due to the replacement of primary plant communities(known as climax) by secondary communities. This replacement modifies the humus composition and amount, and affects the formation of the soil. It is directly related to human activity. Soil degradation may also be viewed as any change or disturbance to the soil perceived to be deleterious or undesirable. L] At the beginning of soil formation, the bare rock out crops is gradually colonized by pioneer species (lichens and mosses). They are succeeded by herbaceous vegetation, shrubs and finally forest. In parallel, the iris humus-bearing horizon is formed (the A horizon), followed by some mineral horizons (B horizons). Each successive stage is characterized by a certain association of soil/vegetation and environment, which defines an ecosystem. After a certain time of parallel evolution between the ground and the vegetation, a state of steady balance is reached. This stage of development is called climax by some ecologists and “natural potential” by others. Succession is the evolution towards climax.

Regardless of its name, the equilibrium stage of primary succession is the highest natural form of velveteen that the environmental factors are capable of producing. The cycles of evolution of soils have very variable durations, between tens. Hundreds and thousands of years for quickly evolving soils (A horizon only) to more than a million of years for slowly developing soils. The same soil may achieve several successive steady state conditions during its existence, as exhibited by the Pigmy forest sequence in Mendocino County, California. Soils naturally reach a state of high productivity, from which they naturally degrade as mineral nutrients are removed from the soil system. Thus older oils are more vulnerable to the effects of induced retrogression and degradation.

Ecological factors influencing soil formation There are two types of ecological factors influencing the evolution of a soil (through alteration and humidification). 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 (boomed). ; A second type of factor is more local, and is related to the original rock and local drainage. This type of factor explains appearance f specialized associations (ex peat bogs). Brotherliness theory Main article: brotherliness The destruction of the vegetation implies the destruction of evolutes 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 brotherliness. ; In wet climate, the conditions are favorable to the deterioration of the rocks (mostly chemically), the development of the agitation and the formation of soils; this period favorable to life is called apostasy. ; In dry climate, the rocks exposed are mostly subjected to mechanical disintegration which produces coarse detrimental materials: this is referred to as rehearsals.

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 ND 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 is the main factor for soil degradation and is due to several mechanisms: water erosion, wind erosion, chemical degradation and physical degradation. Erosion is strongly related to human activity. For example, roads which increase impermeable surfaces lead to streaming and ground loss. Agriculture also accelerates soil erosion (increase of field size, correlated to hedges and ditches removal). Meadows are in regression to the profit of lowed lands.

Spring cultures (sunflower, corn, beet) surfaces are increasing and leave the ground naked in winter. Sloping grounds are gradually colonized by vine. Lastly, use Of herbicides leaves the ground naked between each crop. New cultural practices, such as mechanization also increases the risks of erosion. Fertilization by mineral man urges rather than organic manure gradually destructor the soil. Many scientists[citation needed]observed a gradual decrease of soil organic matter content in soils, as well as a decrease of soil biological activity (in particular, in relation to chemical uses). Lastly, forestation, in particular, is responsible for degradation of forest soils.

Agriculture increases the risk of erosion through its disturbance of vegetation by way of: ; overgrazing of animals ; planting of a monoculture ; row cropping ; tilling or plowing ; crop removal ; land-use conversion Consequences of soil regression and degradation Main article: land degradation ; yields impact: Recent increases in the human population have placed a great strain on the world’s soil systems. More than 6 billion people are now using about 38% of the land area of the Earth to raise crops and livestock. 2] Many soils suffer from various types of degradation, that can ultimately reduce their ability to produce food resources. Slight degradation refers to land where yield potential has been reduced by 10%, moderate degradation refers to a yield decrease from 10-50 96. Severely degraded soils have lost more than 50% of their potential.

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