Soil Erosion at Tshakhuma

AIM


To identify degraded sites that need to be treated and to provide a guideline for practical and cost effective methods that can be used to combat each type of soil erosion.


OBJECTIVES

 

  • To identify causes of soil erosion
  • To improve water retention in the soil
  • To reduce the effects of raindrops splash erosion on exposed soil surface

LITERATURE


Soil erosion is a process that involves wearing away if topsoil. The process involves loosening of the soil particles, blowing or washing away of the soil particles and ends up in the valley and faraway lands or washed away oceans by rivers and streams. Soil erosion is a natural process which has increasingly has been exacerbated by human activities such as agriculture and deforestation. Erosion, it is whether by water, wind or tillage involves three distinct action soil detachment, movement and deposition. Topsoil which is high in organic matter, fertility and soil life is relocated elsewhere on site where it builds up over time or is carried off side where it fills in drainage channels. ( Frank, 1997)

Soil erosion can be caused by many activities such as deforestation which is the major factor responsible for soil erosion. It is the removal of forest cover which function as a binder of the top layer of the soil which increasingly land demand have resulted in enhancing extent of soil erosion. High winds can contribute to soil erosion particularly in dry weather periods. The wind picks up the loose soil particles with its natural force and carries them away to far lands and leaving the soil sculptured. Overgrazing and overstocking has led to reduced ground cover and breakdown of soil particles, giving room for erosion and accelerating the erosive effects by wind and rain. This reduces soil quality and agricultural productivity. (Strahler, 2013)

River and streams when they are full of soil deposits due to sedimentation and the valley level up with the surface, the water begins to wash away the soil at the banks. This erosive activity is evident in most rivers of streams especially during heavy rainfall and a rapid river channel movement. Crops and grasses support the structure of soils, thereby decreasing the amount of soil erosion. Areas with less naturally occurring flora are more susceptible to soil erosion. The physical features of the land also contribute to soil erosion. Land with a high slope will facilitate the process of the rainwater flow rate or runoff saturation in the area, particularly due to the faster movement of the water downhill.(Frank, 1997)

Soil erosion removes valuable topsoil which is the most productive part of the soil profile for agricultural purposes. The loss of this top soil results in lower yields and higher production costs. When topsoil is gone, erosion can cause rills and gullies that make the cultivation of paddocks impossible.The impacts of soil erosion on cropping lands include reduced ability of the soil to store water and nutrients. Exposure of subsoil, which often has poor physical and chemical properties. Higher rates of runoff, shedding water and nutrients otherwise used for crop growth. Loss of newly planted crops. Deposits of silt in low lying areas. Soil erosion increases water run off and run off often carries pollutants with which it negatively impact the surrounding land. Soil erosion results in increased flooding, increased increased sedimentation in rivers and streams, loss of soil nutrients and soil degradation and in extreme cases, desertification.(Turback, 1993)

There are measures which we can use or apply in order to control soil erosion such as planting grass and shrubs, these are effective at stopping soil erosion. This is primarily because plant root tend to hold soil together making it harder to erode. The leaves of the plants also help to reduce the velocity of the raindrop filling on the ground, making it harder for them to dislodge the soil and erode it.Ornamental grass and low, spreading shrubs work best as they leave no areas of bare soil exposed to the elements. The use of conversation tillage which produces a smooth surface that leaves soil vulnerable to erosion. Conversation tillage such as non-till planting, strip rotary tillage and disking leave more of the field surface covered with crop reside that protects the soil from eroding forces. (Frank, 1997)

Strip farming in areas where a slope is particularly steep or there is no alternative method of preventing erosion, planting fields in long strips alternated in a crop rotation system has proven effective. Contour farming planting in rows pattern that run level around hill instead of up and down the slope has been shown to reduce runoff and decrease the risk of water erosion. There are many varieties of fiber, biodegradable, and compost blankets/mats on the market today, and they have all been designed with one aim; to minimize the effects of water erosion on slopes and embankments. Rolled mats are usually made from mulch that is held together by a fiber mesh. They degrade slowly, allowing vegetation that may have been grown in the area to grow and take over the job of protecting the soil from erosion when the mats have finally degraded completely. Compost erosion control blankets act similarly to mulch products but provide organic nutrients that promote vegetation growth, even in areas where germination, moisture management and irrigation could be challenging.(Turback, 1993)

If you are planning on trying to control the erosion on very steep slopes or embankments, sometimes planting vegetation may just not cut it as the slope may be too steep to support anything other than the hardiest grass due to the rapid rate of erosion. If this is the case, you should consider building terraces to help slow down erosion as the vegetation takes hold. Terraces can be made out of anything, from wood to concrete blocks to bio-mechanical solutions like the Cascadia Green Wall that uses Filter Soxx with natural mulch/seed filling and geogrid for structural stability. The beds that are created by the terraces can then be used to plant vegetation such as ornamental plants or grass. Depending on the incline of the slope or embankment, one of the most effective ways to help prevent erosion is to create diversions which will channel excess water down the slope along a predetermined path. One of the simplest ways to do this is to create open ditches or drains by simply digging along the slope at regular intervals. Use of pipes and gutters is also very effective, and work just as well as natural drains when designed and installed properly.(Frank, 1997)


REFERENCES

  • Frank, P and Raymond, S. 1997. Understanding earth 2nd edition London : WH Freeman and Company.
  • Strahler, A. 2013. Introduction Physical Geography, 6th Edition, New Jersey : John Willey and Sons, Inc.
  •  Turback, E.J and Lutgens, K.C. 1993. The earth : an introduction to physical Geology. New York : Maxwell Macmillian