Land Degradation & Soil Erosion

1. Land Degradation & Soil Erosion Introduction Land degradation Soil Erosion Water Erosion Wind Erosion Soil Conservation

2. Land Degradation • This is the reduction of the productive potential of lands for human use. • Land degradation is caused by such phenomena as: • Overgrazing by animals • Deforestation • Inappropriate agric practices • Soil erosion • Two main components of land degradation are; • Damage to plant communities • Soil degradation

3. Soil Erosion Soil Erosion - the detachment and movement and redeposition of soil. Two main types of erosion are: • Natural Erosion - normal geological soil movement by wind, water, ice, or gravity. • Accelerated Erosion - erosion more rapid than natural erosion, primarily as a result of action by humans or other animals.

4. On-Site Effects of Accelerated Erosion Erosion results in the loss of soil itself • The surface horizons which usually contain much of the soil nutrients are eroded. • The subsoil horizons which are less useful remain • The quality of remaining topsoil may also be impaired. • Organic matter is removed • Water holding capacity and cation exchange capacity is lower • Essential nutrients are removed

5. Off-Site Effects of Accelerated Erosion • Erosion moves sediments and nutrients off the land to rivers and lakes • The nutrients impact water quality through the process of eutrophication • Caused by excess nitrogen and phosphorus • Runoff water may also carry toxic metals and organic compounds, e.g., pesticides

6. Sediment Problems • Sediments are major water pollutants and could cause a wide range of environmental damage. • Smother crops and other vegetation • Fill roadside drainage ditches and destroy structures • Problems of turbidity of streams • Prevents sunlight from penetrating water • Reduced photosynthesis • Death of submerged aquatic vegetation • Upsetting aquatic food chain

7. Sediment Problems (contd.) • Health Hazard • The finest particles blow the farthest and present major human health hazards • lung problems

8. Soil Loss Tolerance • Although every soil loss is detrimental, some loss can be tolerated. • Different soils have soil-loss tolerance limits • Tentative soil-loss tolerance limits have been developed for soils • Soil moved annually by erosion in the U.S. equals approximately 5 billion metric tons (2/3 by water, 1/3 by wind). • Average annual cropland soil loss in the US is calculated to be 11 Mg ha-1 y -1

9. Models for Predicting Extent of Soil Loss • Universal Soil Loss Equation (USLE) • Simple model that relates soil erosion to easily observed factors • The main point of this model is the fact that water induced erosion is a result of the interaction of rain and soil

10. A = RKLSCP A, predicted soil loss, is the product of R = rainfall erosivity K = soil erodibility L = slope length S = slope gradient or steepness C = cover and management P = erosion control practices The equation has been modified a bit (RUSLE) to better define the factors and computerize the model

13. Mechanics of Water erosion • Detachment of soil particles from the soil mass • Influence of raindrops (detachment, granulation and movement of soil particles) • Transportation of the detached particles downhill • Floating, rolling, dragging and splashing • Deposition of the transported particles at some place lower in elevation. • Eroded materials can easily travel long distances.

15. Types of Water Erosion • Sheet Erosion • Uniform removal of soil from the land surface • Rill Erosion • Sheet flows begin to concentrate on tiny channels (termed rills) that become dominant –bare lands • Gully Erosion • Volume of runoff may concentrate more and cut deeper into soil. Rill become larger channels –gullies.

17. Water Erosion Control Conservation tillage • Form of tillage that protects the soil from ravages of erosion. • Herbicides (kill weeds chemically rather than mechanically) • Minimum tillage (planting seeds without removing the plant residues.

19. Wind Erosion • Wind erosion is most common in arid and semiarid areas. • It occurs when strong winds blow across soils with relatively dry surface layers. • Finer soil particles can travel very long distances and can cause all kinds of health problems in humans

20. Wind Erosion • Like water erosion, wind erosion involves three processes • Detachment, transportation, and deposition. • Transportation of particles could be by: • Saltation -movement by series of short bounces • Soil creep –movement of large aggregate along surface • Suspension – movement of dust particles parallel to the ground surface and upwards into the atmosphere.

21. Factors Affecting Wind Erosion • Wind velocity • Wind turbulence • Surface roughness • Soil properties • Vegetation.

22. Predicting Wind Erosion • Wind erosion prediction equation (WEQ) E = f(ICKLV) I = soil erodibility factor C = climate factor K = soil-ridge roughness factor L = width of field factor V = vegetative cover factor.