Soil Erosion Global Problem • Soil erosion ranks as one of the most serious environmental problems in the world • 75 billion tons of fertile soil lost annually around the world • Africa, Europe & Australia : 5-10 tons/ha/y • North, Central & South America: 10-20 tons/ha/y • Asia: 30 tons/ha/y • Soils essentially non-renewable as 2.54 cm of soil estimated to take 200-1000 years to form…… • Annual costs of soil erosion in U.S. estimated between $30-44 billion in 2002
WIND EROSION LOSSES IN PAKISTAN• Total area = 79.61 m ha• Cultivated area = 20.61 m ha• Forest area = 3.61 m ha• Area affected by Erosion = 76 %• Affected by Wind Erosion = 40 %
Types of Erosion • Geological erosion (natural) • Accelerated erosion (because of poor management) (Ding Darlington 1947)
Natural Systems Also Experience Erosion In stable forest ecosystems only 0.004-0.05 tons/ha/y of soil arelost by erosion Forests (on average) require 60% forest cover on landscape toprevent erosion Common along banks of streams and rivers (exacerbated bycattle grazing) Wildfires, landslides and other natural disturbances
EROSION• Erosion is a natural process, accelerated by farming activity, that removes topsoil, reduces levels of soil organic matter, and contributes to the breakdown of soil structure.• Erosion is a process by which soil is moved from one area to another. In the geological past, huge volumes of land surface materials were moved by glaciers.• At present, the main natural agents of erosion are wind and water.
• Erosion occurs naturally on cropland, forested land, and in urban areas, but this process can be accelerated by human activity (such as agriculture, forestry, and urban development) to levels that cause environmental and economic problems.
Factors of Wind Erosion E = f(I, C, K, L, V)I is the soil erodibility by wind (related to relative amount of particles > 0.84 mm dia.C is the local wind erosion climatic factor (product of average wind velocity and average moisture of soil surface)K is the soil surface roughness (expressed in height of ridges; more roughness increases resistance to wind erosion)L is the unprotected width of the field (protection provided by wind breaks)V is the equivalent quantity of vegetative cover (includes quantity, kind, and orientation of vegetative cover
Factors Affecting Wind Erosion Several factors relating to soil, landscape and climate that affects wind erosion are • soil texture • soil structure • surface relief • soil protection by plants or plant residues • rainfall • wind force.
• Erosion works on loosely held soil particles at the soil surface.• Silty and very fine sandy soils are particularly vulnerable to erosion.• Poorly structured soils whose aggregates (clumps) have been broken down into fine particles by tillage and other forces are also easily eroded. •Surface relief (shape and slope) affects the direction and rate of erosion. It also affects the location of soil deposition, because eroded soil tends to accumulate at the base of slopes and in depressions.
• Exposed soils suffer greater erosion than soils wellprotected by standing plants or plant residues• Climate affects erosion mainly through the moistureconditions of the soil and specific climatic events (wind andrainstorms).• Soils are most vulnerable to wind erosion when the soilsurface dries out rapidly during periods of low or no rainfall,such as the drought during the "dirty thirties" in the prairiesor in early spring when the soil is not protected byvegetation.• Wind speed and the length of time the wind blows aremajor factors in wind erosion.
Causes of Wind Erosion• Bare, unprotected soil is extremely vulnerable to wind erosion• Erosion occurs with strong, turbulent winds blowing across a soil surface that is smooth, loose, dry and finely granulated.• Slightly larger soil particles bounce or roll along the soil surface.• Loose particles drift along, bombarding and dislodging still more particles with the same effect on clods or growing plants as sandblasting.
SIGNS OF WIND EROSIONSometimes erosion is spotted easily in the field.Common signs of wind erosion include: • Dust clouds • Accumulation of soil along fence lines and banks • Drifted appearance of the soil surface.
WINDEROSION Rarely produces the catastrophic dust storms known as the Dust Bowl in the 1930s in the US, but damages soil like water erosion by removing organic matter and plant nutrients and by decreasing soil thickness
Wind Erosion • Both wind and water behave as fluids, so processes of erosion similar • When the wind force (function of velocity) exceeds forces holding particle in the pedon, it moves the particle
Forms of Wind ErosionSaltation: lifting and bouncing of a particle,mostimportant for particles 0.1 - 0.5 mm dia.Creep: coarse and very coarse sand grains rolled onground surfaceSuspension: Lifting of silt- and clay-sized particles(<0.1 mm) high into the air and can thus be carriedlong distances
Figure 15–21 This hydromulcher is spraying a mixture of seed, fertilizer, and chemicalmulch on the road cut. The chemical mulch holds the seed in place and protects theslope from erosion until the grass germinates and becomes established. (Photo: B. Kay.)
Damages of Wind Erosion• Losing topsoil has a direct effect on the productivity of the land. A loss of 2.5 cm of soil can reduce wheat yields by 5-10% while a loss of 20 cm can reduce yields to 1/3 of their previous levels. Estimated soil loss by wind erosion on the is 160 million tones per year.• As soil productivity decreases due to a decrease in topsoil, soil fertility becomes less.• Organic material is reduced and hence, less plant growth occurs.
•The effect of wind erosion on the soil is the impact of driftingsoil itself.•Young seedlings are uprooted.•Soil covers plants and seeds.•Roads,railways and fences are covered by soil.•It creates air pollution
How to control wind erosion? • Proper soil and range land management is the key to reducing the effects of wind on the land. • Following are the main steps to control wind erosion. • Planting shelterbelts (trees may be obtained from the Tree Nursery) to help reduce the velocity of the wind • Increasing the organic content of the soil • Using fertilizers to increase soil productivity
• Alternating narrow strips of summer fallow and crop perpendicular to the prevailing winds (strip cropping)• Leaving stubble barriers• Using trash cover and green manure• Reducing tillage• Using marginal land for livestock rather thancrop production
• Reducing the speed of tillage• Planting of fall cover crops (winter wheat or rye) inareas of light, sandy soil which are particularly proneto wind erosion• Using marginal land for livestock rather than cropproduction• Reducing the speed of tillage• Planting perennial grass or legumes on grazinglands• Zero tillage - planting crops in to last years stubble
•The more organic material present in the soil, thegreater the resistance of the soil to be broken intoparticles small enough to be carried away by wind orwater, and the more moisture the soil will hold.Adding fertilizers to the soil aids in making the soilmore productive, which protects it against theeffects of erosion.
Some Additional Points For Controlling Wind Erosion • sufficient area upwind should be tilled -- not just the area presently blowing. • The direction of emergency tillage should always be at a right angle to the wind for maximum protection. • For row crops, it may be necessary to compromise by following the row pattern instead of the prevailing winds. If old crop stubble remains, the emergency tillage tool should run between rows, leaving as much upright stubble in the rows as possible. • Tractor speed and tillage depth should be varied as needed to bring clods to the surface. The best, most effective clods come from moist soil. Slower travel speeds with tillage implements will build higher ridges and more protection.