[ Close ]
The word “erode” can best be defined as to eat away, wear out or to destroy the surface. Erosion is the product of erode. Land Degradation is any variation to the original land that diminishes the land value and productivity. There are many types of land degradation. These can be listed as:
When all vegetation has been removed from the soil, the soil is left to become exposed to the elements, leaving it bare and loosening the soil particles. The soil is then easily blown away, leaving poorer quality sub-soil to remain. This is a severe problem in the inland regions of Australia.
Water erosion is not unlike wind erosion, except instead of wind removing the particles; it is due to the force of running water and heavy rainfall. Such events include flash flooding, where sudden rainfall can occur several kilometres away. The water sweeps down, taking with it everything in its path. They uproot trees, move boulders and demolish bridges and buildings, along with the precious topsoil. These floods are very dangerous.
Overgrazing is a common problem in many parts of Australia. It is caused by animals, generally sheep, cattle, or other feral animals, all concentrated in the one area, all feeding on the grass and shrubs. Grass and shrubs hold the soil firmly together. The removal of grass and shrubs leaves the soil bare and susceptible to wind and water erosion. The soil can be broken up or compacted by hooves, this makes the problem worse. It also increases runoff (when water cannot be absorbed into the ground, it ‘runs-off’).
When all the natural vegetation is cleared from the land, groundwater can slowly rise to the surface of the soil because trees intercept the rain water, therefore the water table doesn’t rise. The Water Table rises, as the roots from trees keep it down. The water is very salty and only certain trees can withstand the salinity level. When the water table rises, the salt kills trees and crops that cannot survive the concentration of salt in the water. When the water has evaporated, all that remains is the salt, therefore rendering the soil useless.
When certain chemicals are used on the soil, for various reasons including pesticides; removal of salt from the surface and the soil; acid rain; the growth of certain crops; certain animal wastes; etc, these chemicals are often absorbed into the soil and become part of the soil-structure. With these chemicals now part of the soil, the soil may become acidic and therefore crops and pastures will not grow. Soil acidification can lead to a productivity decline up to and equal to 50%.
Irrigation Salinity and Waterlogging
Irrigation salinity is when the irrigation water, used to provide water for crops and pasture, seeps down to the water table, with all the dissolved salts, rises and kills the crops and grass, as they are not used to the salty soils.
Waterlogging is very similar to irrigation salinity. The only thing that is different is that the farmer irrigates his crops excessively, to the point whereby the water then seeps down to the water table whilst all this extra water saturates the surface, there is more water in which the salts are able to be dissolved.
The Replacement of Natural Vegetation with Pasture
With new pasture, comes new irrigation and more water. The natural vegetation is more adapted to the salinity of the soil and the water table. Most native trees have deep roots that keep the water table down, but if these deep roots are removed then the water table will rise due to more water and by the time that the water table reaches the roots, the pasture will die and the water evaporate, leaving behind salt pans, a crusty formation of salt on the surface. With saltpans on the surface, it is very hard to try and remove the salt from the surface and the soil.
Soil-structure is a complex soil composition. This comprises of air, organic matter, water, mineral particles, nutrients, etc. The different types of organic matter, mineral particles and nutrients make the soil-structure types more diverse. Soil-structure decline is when all these different types of nutrients and organic matter and mineral particles are some how drawn from the soil and leaves limited nutrients remaining in the soil.
Things that can cause soil-structure decline are erosion of any kind, some agricultural cultivation practises, over worked soils that do not have time to replace nutrients etc; the use of pesticides can effect the soil-structure, as the insects’ dead bodies, and wastes contribute to the soil-structure diversity; and the chemicals in some pesticides may have effects on the soil and the structure of the soil, short-term and long-term.
[ Close ]