Effects that wind erosion• The first effect is the winnowing of irradiate particles. Wind erosion is really selective, transferring the ideal particles - specifically organic matter, clay and loam - countless kilometres. The accumulation of this alluvial matter stripped by the wind native the periglacial steppes gave rise come the abundant loess soils that cover big areas of Europe and North America, whereby highly fertile farming has developed.• The most spectacular creates are dunes - mounds of an ext or less sterile sand - which move as the wind bring away them, also burying oases and ancient cities.• destruction of sedimentation crusts on the surface of stripped soils, or the weathering of rocks at your base wherein they room in contact with the floor (abrasion).• Sheets of sand travel close come the floor (30 come 50 metres) can degrade crops (particularly millet or cotton seedlings in semi-arid zones).• Lastly, wind erosion reduce the capacity of the floor to keep nutrients and water, therefore making the setting drier.Factors affect the extent of wind erosion• Aridity the climate. Wind erosion can likewise take location in high-rainfall climates when certain months that the year are particularly dry (but only if the soil is tilled with methods that crush the surface fine). It tends to be slight in Africa, however, except where rainfall is much less than 600 mm; over there are much more than six months there is no rain; potential evapotranspiration above 2000 mm; soils have been left bare; and also the vegetation move from savannah to steppe, through patches of bare soil.Wind-speed likewise has to exceed about 20 km/in or 6 m/s over dried soils. Wind erosion phenomena will increase proportionately in the existence of strong, regular prevailing winds or gusts.• soil texture. Loamy sand, rich in particles in between 10 and 100 microns in size, is the most delicate soil (Bagnold 1937). Much more clayey soil is lot stickier, better-structured, and hence more resistant. Outlet sand and also gravelly or rocky soils room also much more resistant, since the particles room too heavy to be gotten rid of by wind erosion. The optimum dimension for wind erosion is around 80 microns.• floor structure. The less structure-improving matter a soil has on the surface ar (organic matter, iron and complimentary aluminium, lime), the an ext fragile it will certainly be, if the existence of salt or salt often leads to development of a great of dust top top the surface, which fosters wind erosion.• State the the floor surface. If the soil surface is stony, forming a "pavement", the dangers of wind erosion are reduced - as, for example, in regs.A turbulent surface, left by cloddy tillage or ridges perpendicular come the prevailing wind, slows under the wind at ground level, hence reducing saltation.• Vegetation. Stubble and also crop residual water in the soil reduced wind-speed in ~ ground level.• soil moisture boosts cohesion of sand and also loam, temporarily avoiding their erosion through wind.Wind erosion controlWind erosion control is carried out on two fronts: to reduce wind-speed in ~ ground level, and increasing soil cohesion, therefore improving soil resistance come wind.INCREASING floor COHESIONApplications that organic issue in the surface horizons enhance soil structure.Spraying the soil through refinery sludge, heavy oil or bitumen and also plastics industry waste (for example, diluted glue) binding particles come the soil surface ar making it complicated for the wind to remove them (Gand university experiments).Where there is enough water, supplementary irrigation have the right to be one effective and also financially viable means of reduce erosion problems. Irrigating the soil before the normal rainy season is sufficient to permit favourable tillage conditions and also establish tree cover before the disastrous tornadoes which normally come at the start of the rainy season.INCREASING ROUGHNESS that THE soil SURFACEThis involves cropping approaches that leave big clods on the soil surface ar or ridges perpendicular come the direction the the prevailing wind - return ridges have to not be more than 40 centimeter high or the wind will certainly lop off your tops, thus accelerating erosion.Another very effective control method is the of leaving crop residues in the fields. In Burkina Faso, because that example, when millet and also sorghum stubble is reduced at a height of 1 metre and also left vertical to the soil surface, the traps a large amount of dust, together with leaves the tornado winds have blown off the trees.INCREASING plant COVERWind-speed can additionally be reduced by boosting plant density. Due to the fact that this is clearly not basic in arid zones, that is an especially important come ensure sound crop residue management, maintaining residues on the floor so regarding increase roughness and also protect the soil surface, rather than ploughing in, i m sorry would just slightly improve soil structure and also resistance come wind. In the semi-arid tropical conditions of West Africa, the big natural stand of Acacia albida so widespread in grew zones generally provide reasonably effective protection against wind erosion in these fragile areas by cutting wind-speed at ground level, and additionally shedding pipeline onto the ground. Unfortunately, most of this stands are made up of in between 25 and 40 very old trees every hectare and are in urgent require of regeneration. Planting 100 to 150 young trees along the defence lines versus water erosion would offer a great density the adult trees. In locations subject to violent blows indigenous a constant direction, hedges and wind-breaks are popular methods.WIND-BREAKSTheir function is twofold: they cut wind-speed to mitigate both evaporation and also wind erosion. The result of cut wind-speed by 20% is operative over an area 10 come 12 time the height of the obstacle before and also behind it.This protection depends ~ above the permeability of the wind-break, for relative impermeability reduced speed more, yet over a smaller area. According to Heusch (1988), if the speed is cut too much by very close planting, the temperature rises and crops are burned along the wind-break. It would certainly be better to regenerate a stand of about 40 adult trees to cut the wind-speed an ext regularly.In principle; wind-breaks reduce evapotranspiration by up to 20% (although the water consumption of the wind-break itself have the right to offset this confident effect), thus the attraction of windbreaks approximately irrigated crops. In the Keita valley in Niger, a marked rise in returns (+27%) is seen except in the direct vicinity the the wind-breaks, wherein the millet ill from root competition through the root of the wind-break (shade and also competition because that water).The best plan would be 2 rows of high trees surrounding by two rows of low trees, making up a 10-metre piece (Figure 59b), half of which is logged at a time. The cropped area between wind-breaks can be as large as 100 metres if the tall trees room over 5 metres. Source competition is decreased by break the young horizontal root of the tree from the first year onwards by raking the tillage furrow. The is an especially important to fix breaches in a hedge to store the wind from pouring through at these points (the Venturi effect) and also considerably to reduce effectiveness.FIGURE 59

a. Affect of a wind-break ~ above the wind (cf. Combeau 1977)


b. Affect of a wind-break on production of a cereal grain (cf. Guyot 1963)


When the trees are cut, the is finest to leave 2 metres above the soil so that livestock do not destroy new shoots.The most typically grown tree varieties in Africa room eucalyptus, casuarina, neem, various acacias, tamarisk and also cypress - return cypress is prone to a significant disease. Reeds of miscellaneous kinds can additionally be useful.A wind-break go not need to be an extremely thick: the thicker it is, in fact, the much more impervious and thus the less efficient - that becomes. In ~ a street of 10 times the height of the barrier, the wind-speed top top the leeward next is 56% the speed of the local wind behind a line of reeds, 72% behind a 20-m special wind-break, and also 83% behind a 600-m wide forest piece (Combeau 1977).In Niger, Renard and also Van den Beldt (1991) noticed that large quantities of sand were trapped in the strips of Andropogon surrounding their trial plots, and they because of this suggest that farmers have to surround their fields with a dual row the Andropogon. Elsewhere, low crops such together groundnut and cotton are defended by interspersing them v rows of millet and also sorghum, which can reach a height of 4 m. Lastly, although the initial target of windbreaks is that of reduce evaporation caused by the wind, they also help to minimize the quantity of heavy wind-borne matter. The wind must be able to pass with them and not set up eddies, and they have to combine types with complementary forms and also heights and in enough numbers, so that they have the right to be logged in sequence and frequently renewed (Figure 59).DUNE FIXATIONThe suggest of dune fixation is to get rid of the source of sand and also to save the dunes in place, making use of both mechanical and also biological methods. In areas where dangerous winds come from only one direction, wind erosion have the right to be stopped by rows perpendicular come this wind at ranges of 20 times the elevation of the rows. For this reason if millet or sorghum stalks 1 come 1.5 metres high space used, rows should be spaced every 20 metres, or the wind will certainly take increase sand in between these lines of defence. This method that big amounts of product are essential (millet stalks, oleanders which thrive in wadis, palms, or prunings from the forest trees or shrubs discovered in the region), and the removal of this product helps to degrade the area. If - together is regularly the instance - the dangerous winds come native a variety of directions, the use of grids the permeable plastic sheeting v a 5- come 10-mm mesh and a height of 50 to 80 centimeter is indicated. The more powerful the winds, the smaller the grid, ranging from 5 × 5 m to 8 × 8 m in common conditions. Some plastic sheeting, scorched by UV rays, turns to dust after two years, and is because of this to be avoided, while part black UV-resistant plastic deserve to be supplied for 2 years top top one site and also then relocated to another. The main problem is to stretch it and also to have actually solid enough stakes to organize it (12-mm reinforced concrete posts). As shortly as this network is in place and the soil surface has actually become more stable, a selection of grasses and also shrubs have to be planted within it to restore plant cover and also definitively stabilize the dune.Another inexpensive technique well suited to West Africa is that of sowing rows or grids of millet or some various other fast-growing plant in the rainy season, thus offering the soil more stability. If the survive of these fragile planted plots is to be assured, it is obviously crucial to defend them versus grazing and fire, return after five years part light and well-supervised grazing may be possible.In France, the an initial attempts come stabilize seaside dunes were made in the 16th century, once the town of Bayonne had a sand-loving plant sown on the live dunes at lid Breton, followed by reforestation v sea pines. In 1786, Bremontier, a public functions engineer, initiated actions to resolve the sandy heaths near Arcachon, by having actually branches the broom spread over the sand, and sowing with pine. This attempts to be so successful that occupational then ongoing until 1876, spanning 80000 ha and also costing 9.6 million "gold francs" add to 3.5 million for the creation and also upkeep of a long, protective seaside dune to cut the wind-speed and permit the pines come grow.This safety dune 50 metres behind the high water mark has actually a financial institution with a 20% slope encountering the west winds and also planted v Ammophila arenaria, then a flat top, through a palisade on posts along that is axis, then a crumbling financial institution of sand. As soon as the fence is about to be capped by deposits, it is raised again through a gin, until the dune eventually reaches a elevation of 10 metres (in 10 + 2 years). In front and also to the sides, wattling marks off the area to it is in stabilized, and seeds room broadcast within this area, after which the floor is covered with branches the pine, gorse, heath or broom set one end the other like tiles ~ above a roof, v the thick end of the branches pushed right into the ground towards the wind.One hectare will certainly take 25 kg of jaw seed, 15 kg of broom seed, plus gorse and also Ammophila, 120000 15-kg bundles of branches, and 120 days of work, plus the expense of developing the fence (Heusch 1988, p. 184). CONCLUSIONIt is interesting to check out how comparable wind and sheet water erosion room in regards to the processes involved, the impacts on the soil, and also the factors and also control methods. Indeed, one equation very comparable to the USLE has actually been drawn up to projection wind erosion. Wind erosion assumes far-ranging proportions only once the wind dead a fill of sand seed which bombard the bare soil surface, and also sheet erosion occurs when rain splashes on naked soil. Both develops of erosion selectively carry off fine corpuscle from the floor surface, and also both are removed by mulching the soil or by providing an adequate plant cover. Both processes bring about a palliation in fine corpuscle in the surface horizon - or scouring that the whole horizon in the most too much cases. The determinants that deserve to be lugged into play room soil cover, pervious barriers that enable the tool (water or air) come filter slowly, and development of the structure, cohesion and roughness of the tilled horizon.

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The regulate methods space therefore really similar: hedges, windbreaks, keeping chop residues on the soil surface, thick tree cover, outlet tillage, mounding or tied ridging, reduction of the size of areas exposed to prevailing winds or runoff, organic or mineral applications (lime or gypsum), etc. This is why this publishing is border to general principles, referring readers to the many manuals giving details that plant varieties suited to neighborhood dry conditions.

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