Soil Erosion What is soil erosion? ● Soil is a fragile resource - once eroded it cannot be renewed ● Soil erosion is a major problem in many developing countries ○ Sahel region in Africa, parts of Brazil, China ● Soil erosion is also a problem for developing countris ○ highly intensive farming, chemical fertilizers, warmer & drier weather

● Wind and rain can cause soil erosion by carrying away the topsoil ● Overgrazing & over-cropping also cause soil erosion

Countries of the Sahel

Soil Erosion in the Sahel Where is the Sahel? ● Stretches across North Africa - several countries just below the Sahara Desert ● Niger, Chad, Mali, Sudan - all extremely poor ● Soil Erosion - land being over-used leading to wind erosion of topsoil ● Desertification - the Sahara desert is moving southwards turning farmland into desert

Why the Sahel? ● Human Activities ○ Over- grazing - too many animals for the carrying capacity of the land ○ Over- cropping - too many intensive cash crops on marginal land ○ Deforestation - destruction of vegetation cover (trees etc)

● Natural Causes ○ Climate Change - Higher temperatures and decreased rainfall leading to drought

What is overgrazing? ● Too many animals graze the land, damaging the topsoil and destroying vegetation ● Population explosion in Sahel countries (need for larger herds) ● Major increase in cattle & goat herds ● Hooves of cattle compact the soil and destroy soil structure (reduces ability of the soil to retain water) ● Animals destroy vegetation (small trees & shrubs) through grazing ● Roots that anchor the soil are destroyed ● Humus content of the soil is reduced due to decrease in vegetation

Soil erosion in the Sahel

Cattle herd

Dried out soil

Overgrazing continued ● Decrease in grass cover exposes the top soil to heat and wind leading to erosion

● Change to settled farming practices ○ Sahel farmers used to be nomadic (moving from place to place) ○ Today - farmers settle in one place to farm more intensively ○ leads to damage to soil structure, destruction of vegetation ○ Also lead to water loss due to increased number of well being drilled

What is over-cropping? ● When land is continously farmed and not fertilized ● Land is not left to rest & not fertilized adequately ● Nutrients are drained from the soil making it infertile ○ this reduces humus production ● Overcropping is the result of population explosion more food is required ○ ● Overcropping is also caused by planting intensive cash crops to generate hard currency income (US dollars) ○ developing countries in the Sahel have large debts owed to ○

international lenders Cash crops are sold on international markets to make money

Over-cropping continued ● What are cash crops? ○ Tobacco, Cotton, Cashew nuts ○ make intensive use of the soil ○ planted every year to generate foreign income

● What is Monoculture? ○ The same crops (cash crops) is grown every year ○ Certain nutrients (e.g. phosphorous) are drained from the soil ○ Sahel farmers lack the money to buy sufficient fertilizer ○ Monoculture is huge plantations of sugar cane, cotton, tobacco, cashew nuts

Cash Crops

Cotton Plantation

Cashew Nuts

Deforestation & Soil Erosion ● Trees provide cover from wind and rain for the soil ● Also anchor the soil through tree roots ● What is happening in the Sahel? ○ ○ ○ ○ ○ ○ ○

Trees and shrubs are being cut down for fuel Trees are not re-planted (lack of money) Cattle dung is used for fuel instead of trees Lack of cattle dung deprives land of valuable fertilizer Intense heat dries out the soil and allows top soil to be blown away Land becomes desertified (Desertification) Land is abandoned over time as desert spreads

Climate Change & Soil Erosion ● Climate Change is a natural cause (perhaps man-made?) ● Increased temperatures in the Sahel region ● Rainy season is no longer dependable ● 30% decrease in rainfall levels in the last 30 years ● Droughts are longer lasting - soil dries out and gets blown away ● Famine has resulted - Niger, Ethiopia. ● Wars over access to water - Sudan

Climate Change & Rainfall Reduced rainfall since 1970s

Terrible famine of 1985/85

Effects of climate change Sahel badly effected by climate change Sahel Region

What can be done? ● Building Stone walls ○ stone wall keep water from flowing downhill & allow it to percolate the soil

● Wind-breaks (Tree planting) ○ ○ ○ ○

barriers formed by tree planting & grasses Stops wind from blowing away soil important for planting wheat (prevents soil erosion) Windbreaks can also provide timber for fuel & building ○ Roots anchor the soil ○ Helps water percolate the soil

What can be done? ● Contour ploughing ○ ploughing across the slope / hill rather than up or down ○ Dangerous for machine operator ○ prevents rain eroding topsoil

● Stubble planting ○ Used in rich countries, eg. Ireland ○ stubble (remains of cut wheat) is left on the field ○ New crops & fertilizer are inserted into soil using modern seed drills ○ No need for ploughing the field - prevents wind and rain erosion

To sum up ...... Over-grazing, over-cropping, deforestation and climate change all interact in a complex way to produce soil erosion and desertification in the Sahel BBC on food crisis in West Africa 2012