Dr HH Mate
The practice of arresting or minimizing artificially accelerating soil deterioration is called soil conservation. Its importance has grown because cultivation of soils for agricultural production, deforestation and forest cutting, grazing of natural range, and other disturbances of the natural cover and position of the soil have increased greatly since the middle of the nineteenth century in response to the growth in world population and human technical capacity. Accelerated soil deterioration has been the unfortunate consequence:
Types of Soil deterioration: Soil may deteriorate either by physical movement of particles from a given site or by depletion of the water- soluble elements in the soil which contribute to the nourishment of crop plants, grasses, and other economically usable vegetation. The physical movement generally is referred to as erosion. Wind, water, glacial ice, animals, and tools in use may be agents of erosion. For purposes of soil conservation, the two most important agents of erosion are wind and water especially as their effects are intensified by the disturbance of natural cover or soil position.
Water erosion always implies the movement of soil downgrade from its original site. Eroded sediments may be deposited relatively closed to their original location, or they may be moved all the way to a final resting place on the ocean floor. Wind erosion, on the other hand, may move sediments in any direction, depositing them quite without regard to surface configuration. Both without regard to surface configuration. Both processes, along with erosion by glacial ice, are part of the normal physiographic or geologic processes which are continuously acting upon the surface of the Earth. The action of both wind and water is vividly illustrated in the scenery of arid region. Soil conservation is not so much concerned with these normal processes as with the new force given to them by human land-use practices.
Accelerated erosion may be induced by any land use practice which denudes the soil surfaces of vegetative cover. If the soil is to be moved by water, it must be on a slope. The cultivation of a corn or a cotton field is a clear example of such a practice. Corn and cotton are row crops, cultivation of any crop on a slope without soil conserving practices is an invitation to accelerated erosion. Cultivation of other crops, like the small grains, also may induce accelerated erosion, especially where fields are kept bare between crops to store moisture. Forest cutting, overgrazing, grading for highway use, urban land use, or preparation for other large scale engineering works also may speed the natural erosion of soil.
Where and when the soil surface is denuded, the movement of soil particles may proceed through splash erosion, sheet erosion, rill erosion, gullying, and wind movement. Splash erosion is the minute displacement of surface particles caused by the impact of falling rain. Sheet erosion is the gradual downslope migration of surface particles, partly with the aid of splash, but not in any defined rill or channel. Rills are tiny channels formed where small amounts of water concentrate in flow. Gullies are V-shaped or U- shaped channels of varying depths and sizes.
A gully is formed where water concentrates in a rivulet or large stream during period of storm.
It may be linear or dendritic (branched) in pattern, and with the right slope and soil conditions may reach depths of 50ft or 15 miles or more. Gullying is the most serious form of water erosion because of the sharp physical change it causes in the contour of the land, and because of its nearly complete removal of the soil cover in all horizons. On the edges of the more permanent stream channels, bank erosion is another form of soil movement.
Depletion of soil nutrients obviously is a part of soil erosion. However, such depletion may take place in the absence of any noticeable amount of erosion. The disappearance of naturally stored nitrogen, potash, phosphate, and some trace elements from the soil also affects the usability of the soil for human purposes. The natural fertility of virgin soils always is depleted over time as cultivation continues, but the rate of depletion is highly dependent on management practices.
Economic and Social consequences: Where the geographical incidence of soil erosion has been extensive, the damages have been of the deepest social consequences. Advanced stages of erosion may remove all soil and therefore all capacity for production.
More frequently it removes the most productive layers of the soil-those having the highest capacity for retention of moisture, the highest soil nutrient content and the most ready response to artificial fertilization. Where gullying or dune formation takes place, erosion may make cultivation physically difficult or impossible. Thus, depending on extent, accelerated erosion may affect productivity over a wide area.
At its worst, it may cause the total disappearance of productivity, as on the now bare, lime-stone slopes of many Mediterranean mountains.At the other extreme may be the slight depression of crop yields which may follow the progress of sheet erosion over short periods. In the case of forest soil losses, except where the entire soil cover disappears, the effect may not be felt for decades, corresponding to the growth cycle of given tree species. Agriculturally, however, losses are opt to be felt within a matter of a few years.
To be contd
The writer/author is the eminent educationist sociologist and researcher/scientist.
He can be reached at [email protected]