Preventing Soil Erosion

Just thought I'd elaborate on what can be done to prevent or reduce soil erosion, taken from another textbook and some are my classwork. :) 

The world's population continues to increase, so farmers are going to have to produce more food in order to feed the extra numbers. This can only be done if the soil is protected and carefully managed. [Note: Soil is a renewable resource, but it needs careful management. In the UK, it takes about 400 years just for 1cm of soil to form, and it can take 12,000 years for soil to become deep enough for farming!]

Evidence suggests that in the year 2000, 20% of land that was arable (used/suitable for growing crops) in 1985 had been lost through erosion, desertification and conversion to non-agricultural uses. 

1. Terracing in Indonesia and the Philippines: Large areas of these two countries are covered in volcanic mountains which have steep slopes and fertile soil. Flat terraces (like giant steps) were first built on many of the hillsides, the terraces are flat and are fronted by a mud/stone wall known as a 'bund'. The bund traps rainwater and soil, allowing the rainwater time to infiltrate into the ground so surface run-off and the removal of topsoil is prevented.

2. Contour ploughing: This is ploughing around hillsides rather than up and down the slope. By ploughing parallel to the contours, the furrows trap rainwater and prevent the water from washing soil downhill. 

3. Strip cropping: This is when 2 or more crops are planted in the same field. One crop may grow in the shelter of a taller crop. It is harvested at a different time of the year and uses different nutrients from the soil. Often the crops are rotated from year to year. 

4. Animal welfare in Kenya (Controlled size of herds!): Large herds of cattle, goats, sheep and camels have long been considered a source of wealth and prestige in several African countries. Unfortunately, quantity, rather than quality, has tended to result in overgrazing. [Overgrazing: when pasture or grazing is unable to support the number of animals relying on it for food. The result is that vegetation cover declines and soil erosion sets in.]

The problem of overgrazing has increased partly because rainfall has become even less reliable and partly because of the rapidly growing population. 'Practical Action', a British organisation, is working with local people in several parts of Kenya. They are helping to train one person from each village to become a 'wasaidizi' or animal care worker. By recognising and being able to treat basic animal illnesses, the wasaidizi is improving the quality of local herds. As the quality improves there should be less need for so many animals so that, hopefully, overgrazing will be reduced. 

5. Stone lines ('magic stones') in Burkina Faso: This project, begun by Oxfam in 1979, uses appropriate technology, local knowledge and local raw materials. It involves all villagers collecting some of the many stones lying around their village. The stones are laid across the land to stop surface run-off following the all too rare heavy rainstorms. Water and soil are trapped. The water now has time to infiltrate instead of being lost immediately through surface run-off. The soil soon becomes deep enough for the planting of crops. Erosion is reduced and crop yields have increased by as much as 50%. The only equipment needed is a simple level, developed by Oxfam, to help keep the lines parallel to the contours. 

6. Shelter belts of trees block wind: trees block wind from blowing away loose, dry grains of soil so topsoil is not lost. 

7. Afforestation: Increasing vegetation cover would help slow run off and increase infiltration. Trees intercept rainfall so force of water doesn't hit the soil and wash it away, roots also bind soil particles together. 

8. Small hedged fields: hedges reduce surface run-off and allow time for infiltration so water is retained where it falls. 

9. Gully filled with soil and planted with grasses: prevent wearing of soil and reduce surface run-off. (gullies are like storm drains, they would carry away the rain and soil quickly)

10. Crop rotation and NO monoculture: Practice of growing a series of dissimilar types of crops in the same area in sequential seasons. So that crops don't exhaust nutrients in soil as different crops require different nutrients.

11. Fields left under grass in winter: after winter when snow melts it will infiltrate into soil and stimulate growth of the grass--allowing animals a place to graze, and may prevent ground from freezing hard completely. 

12. Fallow land: crop land that is not seeded for a season, serves to accumulate moisture in dry regions or to check weeds/plant diseases. 'Rests' the land, so soil nutrients can be replenished.

13. Natural fertiliser (manure) used wherever possible: manure puts vital nutrients back into the soil, maintaining its health. And animal manure could be cheaper than chemicals, especially if the farm has some livestock. 

Soil erosion (Types and Causes)

Go to page 180 of Edexcel Geography book, I've adapted the page here, and have added some explanations where I thought they were needed. :)

Soil erosion is the washing away or blowing away of top soil. Basically the wearing away and loss of exposed top soil, mainly by the action of wind and rain (as surface run-off). 

Soil erosion can result in reduce soil fertility. It is a natural process, but it is made worse by people.

There are three main types of soil erosion:

• sheet erosion: occurs in parts of the world where there is moderate rainfall. When this falls on bare soil, the top of the soil will be removed down slope. 
• gully erosion: where there is intense rainfall, as during tropical storms, the force of the water can cut gullies in slopes. This is most likely to happen where there is little vegetation cover. 
• wind erosion: in dry parts of the world, loose dry soil is readily blown away by the wind

Thus, areas most at risk of soil erosion:
-mountainous areas with steep slopes (e.g. Himalaya slopes in Nepal), so the topsoil is removed as rain flows downslope. One quarter of a million tonnes of topsoil are washed off the deforested mountain slopes of Nepal and northern India each year only to be deposited into the Bay of Bengal.
-areas with unreliable rainfall, as the soil dries and becomes really light so the wind can carry it away quickly

Also keep in mind that exposed soil doesn't just get washed downhill by water, it can move downwards slowly under gravity too. Soil erosion can be particularly bad during wet seasons as it is washed away by the storms and it is blown away during dry season..

Soil erosion is made more rapid and severe where there is misuse of the land.
Activities that cause problems include:

• removing vegetation by cutting down trees and bushes for fuel or to make way for more farmland. This exposes the soil to the wind and rain.
• overgrazing by animals-rearing too many animals in relation to amount of grass available. Result: ditto above.
• overcultivating the soil by failing to 'feed' it with fertilisers or by growing the same crop  in the same field year after year. This monoculture weakens the soil structure and removes vital minerals from the soil. (The same crop uses up the same nutrients until it is all depleted.) The net result is that crops will fail and the soil will be left exposed to the forces of erosion. 
• compacting the soil by the use of heavy machinery. (e.g. if a tractor went over a patch of soil, the weight of it would increase pressure on the soil, squashing it together and making it more compact.) This reduces the rate at which rainwater is able to infiltrate the soil. So much of the rainwater flows across the soil surface and erodes the soil as it does so. 
• ploughing fields in the same direction as the slope. This readily encourages gullying. (Ploughing up and down hill creates channels down which rain water can flow. Increases amount and speed of surface run-off.)

In general, you can say that the threat of soil erosion increases with the sparseness (lack of) of vegetation. It also does so where population numbers are so great that they put pressure on the land. (E.g. increase in population means more food is needed, so farmers try to grow more crops but on the same piece of land..growing crops so intensively to feed a growing population can only result in decreasing fertility of the soil, especially when fertilisers are not added to replenish nutrients taken up by the crop!)