Rural Land Degradation

Weathering

The Prairies of the U.S.A. and marginal lands of North Africa are subject to weathering by the following processes:

Model Answer:
Describe in detail the processes of water erosion that contribute to the growth of deserts in North Africa. (8)
Rain splash occurs when raindrops break up the surface of the soil. During heavy tropical storms, borne out of the Gulf of Guinea, the droplet size can be large and this increases the damage. When it happens on a slope the particles thrown up are transported down slope by gravity increasing the damage. When the rain is sustained the ground may become saturated, this means no more infiltration can take place and the water will flow over the surface and carry away large quantities of topsoil. Rilling occurs when surface run off causes shallow channels to form on the soil surface, these are normally temporary. However in areas where heavy rains deepen and widen a rill into a gully these features can become permanent.

 

RLD in the USA

Causes:

Describe and explain how human and physical factors have led to desertification in North America. (10)


Physical: the Rocky Mountains create a rain shadow over the Prairie states and this causes rainfall to be slight leading to dry conditions. The physical distance of the states from the Gulf of Mexico means rain clouds often don’t reach far enough in land so the soil can become dry.  Changes in wind direction cause rain clouds to be diverted away from the Prairie States and lead to unreliable rainfall meaning farmer’s crops may fail. The generally high temperatures cause high levels of evaporation and this leads to baking of the ground which reduces infiltration and can encourage sheet wash. The barren plains of the prairies have few breaks for the wind leading to high levels of wind erosion where the soil is exposed.   


Human: bad farming practices such as using a deep plough in the shallow prairie soils can destroy the crumb structure making the soil easier to blow away. Farmers may also not rotate crops or may not make use of fallow field systems, over use of the land in this way causes nutrients in the soil to be used up and not replaced. Monoculture of water hungry crops such as cotton cause ground water to be depleted. Overgrazing of the land by cattle causes the land to be stripped bare of vegetation which exposes the soil to wind erosion. Cattle are heavy and their weight will cause compression of the pore spaces within the soil reducing its capacity for infiltration, sheet wash will therefore be increased. Cattle also have sharp hooves which powder the topsoil up and cause it to be suspended high up in the air.

Impacts:

The impacts of RLD in the U.S.A. can be broken down into the following categories. Revise them in this order and it will form basis for your answer structure.

Economic

Environmental

Social

Joblessness

Over 1 million ha of topsoil lost

Poverty

GNP of USA suffers from failure of Wheat

Gullying a more common feature of landscape

Depression/suicide rates increase

Amalgamation of small farms into larger farms owned by one richer farmer

Ghost towns

Migration of Okies from Olahoma to fruit picking farms in California.

Local economies dependent on farming suffer

Dust storm of the 1930s Oklahoma Dust Bowl

Rural depopulation as people move away

Solutions:

You’ll need to refer to real strategies that have been implemented to solve the problems associated with RLD in the U.S.A. and also talk about their efficacy. Consult the table and model answer beneath to see how to best answer these questions. Follow the rows of the table in order, each provides a basic answer structure: name the solution; describe it in detail; evaluate its efficacy.

Solution

Detail

Efficacy

Soil Conservation Service

SCS set up to teach farmers better farming practices such as those listed below.

Largely regarded as successful as the Prairies are being sustainably farmed today.

Contour ploughing

Ploughing around the contours of hills to reduce run-off and increase infiltration and storage.

Uses existing machinery, easy to do. Prairies are often very flat and there can be few contours to follow.

Ploughing at 90° to the prevailing wind direction

Ploughing at 90° to the wind means the wind is disrupted and loses erosive power

Disruption to the wind is only slight. Requires no new investment. Is easy to do.

Minimum tillage

Puncture holes about 60cm apart into which the seed is planted with the aim of disrupting the soil’s surface as little as possible.

Weeds and insects invade the unploughed soil with ease. The soil is held together better by not being ploughed.

Sweep ploughing

A special plough blade invented to pass beneath the soil surface cutting crops off at the root without churning up the soil.

Reduces the chances of wind erosion. Requires expensive new equipment and therefore needs investment. Also requires specialist training.

Mulching

Leaving the stalks of the harvest on the ground disrupts the wind and returns nutrition to the soil

Rebalances the soil’s nutrient load. This is a labour saving technique.

Strip cropping

Farming two crop types in alternating parallel rows means that harvest can be staggered so that there is always a plant in the soil to hold it together.

Makes produce for sale at the same time as holding soil together and providing a wind break and shade from the sun. Takes time to implement – not a quick fix.

Wind breaks

These can shelter land from prairie winds for up to 100m

Next to impossible to put wind breaks across the whole prairie, also slow to grow – not an immediate solution.

Afforestation

Planting trees in hilly areas (such as the Tennessee River Valley) prevents sheet wash and rain splash as trees intercept and therefore store moisture.

Roots of trees hold soil together well and trees can provide sustainable employment in the form of logging. However, trees are slow to grow and won’t grow where the soil has already been lost.

Crop rotation and fallow field systems

These simple techniques mean the land can rest to restore its natural balance of nutrients

This means the farmer will have to reduce his yields.

Use of fertilizers and pesticides

These increase yields and therefore profits. Soil is healthier and can be farmed more intensively.

Chemicals are expensive and do damage to local habitats.

Mechanization

In the modern era satellite technology has been introduced to identify areas that are drying out and to trigger sprinkler irrigation systems to solve the problem remotely.

New technology is expensive, requires specialist training, favours larger companies over small individual owners and results in unemployment as workers are replaced by machine.

 

RLD in North Africa

Causes:

Describe and explain how human and physical factors have led to desertification in North Africa. (10)


Physical: Climate change is causing longer periods of high temperatures. High temperatures cause increased rates of evaporation which bakes the ground and reduces the soil’s ability to absorb water. Seasonal rains arrive twice a year and cause periodic down-pours. These tropical down-pours increase the impact of rain splash, they also encourage farmers to farm in narrow windows of opportunity which increases the amount of farming on marginal land. The Harmattan winds arrive from the NE out of the Sahara Desert and help to dry the soil out whilst also increasing processes of wind erosion. Burkina Faso is land locked which means Tropical Maritime air masses arriving from the Gulf of Guinea cannot reach far 3nough in land causing drought conditions.

Human: Nomadic communities are forced out of marginal lands into the interior of Burkina Faso and this adds to population pressure. As a result, deforestation for firewood has occurred and an area of 50km has been cleared surrounding Ouagadougou the capital city. Due to this population pressure, farmers often feel forced into using marginal land for growing essential food supplies which it is already too weak to support.  Wealth is often measured in head of cattle in North Africa and this encourages over-herding of cattle.  The cows’ weight compresses the pore space in the soil and reduces rates of infiltration. The cattle have sharp hooves which break up the soil’s crumb structure reducing it to powder ready to be blown away. Lack of knowledge about sustainable farming practices such as contour ploughing, or fencing in cattle exacerbate problems.

Impacts:

The impacts of RLD in North Africa can be broken down into the following categories. Revise them in this order and it will form basis for your answer structure.

Economic

Environmental

Social

Joblessness

Topsoil permanently lost, deserts expand.

Poverty

GNP of Sahel States suffers from failure of cash crops such as coffee

Gullying a more common feature of landscape

Depression/suicide rates increase

Indebtedness of Sahel states increases as international aid becomes necessary.

Dust storms.

Migration of nomadic tribes to Ougadougou as increased pressure is placed on marginal land.

Local economies dependent on farming suffer

Bare earth and barren horizons from deforestation and over-grazing.

Tension even conflict occur over rights to farmable lands.

Solutions:

You’ll need to refer to real strategies that have been implemented to solve the problems associated with RLD in the North of Africa and also talk about their efficacy. Consult the table and model answer beneath to see how to best answer these questions. Follow the rows of the table in order, each provides a basic answer structure: name the solution; describe it in detail; evaluate its efficacy.

Solution

Detail

Efficacy

Contour ploughing

Ploughing around the contours of hills to reduce run-off and increase infiltration and storage.

Uses existing machinery, easy to do. Prairies are often very flat and there can be few contours to follow.

Ploughing at 90° to the prevailing wind direction

Ploughing at 90° to the wind means the wind is disrupted and loses erosive power

Disruption to the wind is only slight. Requires no new investment. Is easy to do.

Terracing

Otherwise known as Fanya juu in Kenya. Fanya juu means "throw the soil up" in Kiswahili. The terraces formed are ideal for fodder grasses and help prevent soil erosion.

Cultivation becomes easier as the terraces spread out to make the land more level and when combined with manure/fertilizer yields increase. Very labour intensive.

Daguettes

These stone lines are laid along the contours. Farmers use a hose with water in to find the contours as the contour is horizontal the water should not flow out.

Only effective where there is a ready supply of rocks. These are simple to use and as soil builds up behind them so the fields become level so infiltration is increased.

Afforestation

Planting trees to hold soil together with roots and provide shade which reduces evaporation. Trees also provide a wind break and store moisture.

Trees are usually slow to grow however Acacia trees are used which are fast growing and this stops them being swamped by dunes. The trees also produce fuel wood, seeds for consumption and other valuable products such as essence for perfume.

Strip cropping

Farming two crop types in alternating parallel rows means that harvest can be staggered so that there is always a plant in the soil to hold it together.

Makes produce for sale at the same time as holding soil together and providing a wind break and shade from the sun. Takes time to implement – not a quick fix.

Wind breaks

These can shelter land from desert winds for up to 100m

Next to impossible to put wind breaks across the whole desert, also slow to grow – not an immediate solution.

Zai

These shallow pits capture limited rainfall and create ‘islands’ of fertility in which small ecosystems can be gradually supported.

Slow to take effect and subject to ongoing erosion so maintenance is necessary.

Crop rotation and fallow field systems

These simple techniques mean the land can rest to restore its natural balance of nutrients

This means the farmer will have to reduce his yields.

Use of fertilizers and pesticides

These increase yields and therefore profits. Soil is healthier and can be farmed more intensively.

Chemicals are expensive and do damage to local habitats.

Mechanization

Appropriate technology such as wind powered irrigation pumps or biogas energy stations.

These technologies are cheap to install, made from local resources and easy to maintain. Furthermore they are environmentally sustainable.

Watch these videos to find out more. Take notes and build your own answer using whichever techniques sound best or are easiest to remember. Aim to have 7 techniques memorised.

Fanya Juu

Zai

Stone Lines

Demi-Lunes