Soil erosion is a natural process. It becomes a problem when human activity causes it to occur much faster than under natural conditions.
CAUSES OF SOIL EROSION
Wind and water are the main agents of soil erosion. The amount of soil they can carry away is influenced by two related factors:
* speed - the faster either moves, the more soil it can erode;
* plant cover - plants protect the soil and in their absence wind and water can do much more damage.
THE IMPORTANCE OF PLANTS
Plants provide protective cover on the land and prevent soil erosion for the following reasons:
* The plants slow down water as it flows over the land (runoff) and this allows much of the rain to soak into the ground;
* The plant roots hold the soil in position and prevent it from being washed away;
*The plants break the impact of a raindrop before it hits the soil, thus reducing its ability to erode;
*The plants in wetlands and on the banks of rivers are of particular importance as they slow down the flow of the water and their roots bind the soil, thus preventing erosion.
The loss of protective vegetation through deforestation, over-grazing, ploughing, and fire makes soil vulnerable to being swept away by wind and water. In addition, over-cultivation and compaction cause the soil to lose its structure and cohesion and it becomes more easily eroded. Erosion will remove the top-soil first. Once this nutrient-rich layer of soil is gone, few plants will grow in the soil again. Without soil and plants the land becomes desert-like and unable to support life - this process is called desertification. It is very difficult and often impossible to restore desertified land.