05-12-2012, 11:45 AM
SOIL DEGRADATION AND DESERTIFICATION
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DEFINATION:
"’Land degradation’ means reduction or loss of the biological or economic productivity and complexity of rainfed cropland, irrigated cropland, or range, pasture, forest and woodlands resulting from land uses or from a process or combination of processes, including processes
arising from human activities and habitation patterns,
Types of soil degradation include:
Soil erosion by water: the removal of soil
particles by the action of water. Usually
seen as sheet erosion (a more or less uniform
removal of a thin layer of topsoil), rill erosion
(small channels in the field) or gully erosion (large channels, similar to incised rivers). One important
feature of soil erosion by water is the selective removal of the finer and more fertile fraction of the soil.
CAUSES
Clearing land for the purposes of agricultural land, wood for fuel, timber for construction of houses and furniture causes land degradation. Clearing of vegetation and forests degrades land because it leaves the land bare and exposed to wind and water. This two elements cause massive erosion as they wash away the top layers of the soil that is rich and organic, and can support agriculture.
Intense farming and other poor farming practices also causes depletion of soil nutrients. This is because the chemical fertilizers applied to accelerate production of crops kills the naturally occurring soil nutrients. Poor irrigation practices like irrigating with water that contains sodium bicarbonate leads to soil alkanisation, which leads to poor soil structure.
Quarrying of sand, stone, minerals and ore also disturbs the land or changes the landscape of a given environment. The presence of a quarry near a residential area poses danger to the people living around it. This is because it can be breeding grounds for diseases vectors like mosquitoes. Water-filled quarries are also dangerous swimming places and there are statistics everywhere of people drowning in quarries.
Rural to urban migration has led to the emergence of urban sprawls. This is because there is high demand for places to live for the hundreds and hundreds of poor city dwellers. As a result many cities have seen the mushrooming of slums with close to no sanitation facilities, non-existent waste management mechanisms. All these lead to land degradation.
Overpopulation also indirectly causes land degradation; this is because there is increased demand for land for agricultural use. This also results in good agricultural land being saturated and over-farmed hence leading to soil infertility. With population increase and the demand for food comes the need for more water, for a place that experiences less than adequate rainfall, this demand leads to over-drafting; a process that affects the quantity of ground water. In over-drafting, the rate of underground water harvesting exceeds the rate at which nature replenishes the aquifers.
EFFECTS
The main outcome of land degradation is a substantial reduction in the productivity of the land.[5] The major stresses on vulnerable land include:
Accelerated soil erosion by wind and water
Soil acidification and the formation of acid sulfate soil resulting in barren soil
Soil alkalinisation owing to irrigation with water containing sodium bicarbonate leading to poor soil structure and reduced crop yields
Soil salination in irrigated land requiring soil salinity control to reclaim the land [6]
Soil waterlogging in irrigated land which calls for some form of subsurface land drainage to remediate the negative effects [6]
Destruction of soil structure including loss of organic matter.
SOIL DEGRADATION AND DESERTIFICATION
Waterlogging: caused by a rise in groundwater close to the soil surface or inadequate drainage of surface water, often resulting from poor irrigation management. As a result of waterlogging, water saturates the root zone leading to oxygen deficiency.
Increase in salts: this could either be salinization, an increase in salt in the soil
water solution, or sodication, an increase of sodium cations (Na+) on the soil particles.
Salinization often occurs in conjunction with poor irrigation management. Mostly,
sodication tends to occur naturally. Areas where the water table fluctuates may be
prone to sodication.
Sedimentation or 'soil burial': this may occur through flooding, where fertile soil is buried under less fertile sediments; or wind blows, where sand inundates grazing lands; or catastrophic events such as volcanic
eruptions.