Soil Erosion

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As long ago as 1970 when MAFF commissioned the Strutt Report, Modern Farming and the Soil, people were aware of the  concept of soil erosion. The Strutt report concluded that:

'Some soils are now suffering from dangerously low organic matter levels and could not be expected to sustain the farming systems which have been imposed upon them.'

Crop yields have improved dramatically in the last 50 years, at a cost to soil organic matter levels as a direct result of cultivations, especially in the intensively farmed arable areas. The biological activity of the soil, which depends on the availability of nutrients and energy supplied by the soil organic matter and crop and livestock residues has declined correspondingly. (chart below) 

Source: SSLRC, National Soil Inventory, MAFF project (1998)           

Much of the chemical weathering that takes place in soils is the result of the activities of soil micro-organisms, if this biological activity is reduced as a consequence of reduced organic matter levels, then the soils ability to provide nutrients for growing crops will be reduced. 

Care is needed to maintain soils in fertile condition  and to prevent or minimise economic and environmental impacts of erosion. Soil erosion can be loosely defined as:

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The loss of soil by the action of rainfall, run off or wind

The consequences of which:

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Eroded soil may be deposited on other land or in water courses, rivers, lakes, estuaries 

Both the photographs above were taken after long periods of rain, both exhibited 'muddy water' directly attributable to soil erosion

Water erosion is judged to be the more serious of the two types and it has been estimated that:

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Worldwide up to 75 billion tonnes of topsoil are eroded every year equating to:

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c. 9 million ha. of productive land lost

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80% of worlds agricultural soils are affected by erosion. Thompson (1995)

Soil erosion is effected by:

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Rainfall

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Crop rotations

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Amount of crop cover

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Soil type

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Topography

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Length of fallow time

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Cultivation practices

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Size of machinery

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Size of fields

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Height and type of field boundaries (hedges, trees, woodlands etc. - wind erosion)

Pause for thought..... List 5 aspects of crop rotation which may predispose soils to erosion.

The most vulnerable areas for water erosion in the UK are sandy soils in:

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SW and SE England

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East Anglia

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The Midlands

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South Wales

Sandy soil (left) is far more vulnerable to erosion then silty or clay soils (right) as can be seen from the gully created by movement of water on bare land

Chalky soils on the:

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Wolds

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South Downs

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East Anglia

Wind erosion:

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Bare sandy and Peaty soils between March and June in:

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East Anglia

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Vale of York

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East Midlands

Soil erosion has increased in recent years, and problems can occur almost anywhere in the country owing to:

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Late sown winter cereal crops

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The use of tramlines

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Other wheelings

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The need for fine, flat seedbeds for both arable and vegetable crops to aid establishment and pesticide efficiency

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Increase in the length of slopes through hedgerow removal

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The substitution of maize silage for grass in some areas of the country

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Out wintering and supplementary feeding of livestock

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Outdoor pig units on unsuitable sites

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Ploughing and/or reseeding of grassland on slopes

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Damage to river banks by grazing livestock

Wheel marks (left) allow water to move along the surface eroding the surrounding soil. Livestock erosion on a riverbank (right)

Pause for thought.......In a farm situation, how would you assess whether you had a soil erosion problem?

Economic and environmental effects of soil erosion

Repeated erosion reduces the fertility of the soil by:

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Removal of topsoil that is rich in crop nutrients and organic matter

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Reduction of the depth of soil available for rooting, and water storage for crop growth

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Reducing infiltration of water into soil, thereby increasing run off and erosion 

Short term damage and increased costs can result from:

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Loss of seeds, seedlings, fertilizer (see nitrate leaching) and pesticides

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The need to repeat field operations

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Soil being washed from plant roots

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Young plants being 'sandblasted' (wind erosion)

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Extra cultivations to level out eroded surfaces

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Increased difficulty (therefore fuel consumption and man hours) of field operations

Damage to the environment can include:

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Deposition of sediment onto roads, neighbouring properties and into drains.

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Damage to the quality of water courses, lakes and rivers through excess inputs and increased chemical loading.

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Increased run off and sedimentation causing a greater flood hazard downstream

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Sediment in rivers damaging the spawning grounds of fish

Rivers can cause erosion problems on unprotected banks. Livestock poaching (right) can lead to more serious erosion problems

Prevention of water erosion:

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Reduce run off onto fields from farm roads, tracks and areas of concrete by provision of adequate drains, ditches and soakaways

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Maintain land drains, ditches and outlets to ensure effective field drainage

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Remove sediment that has deposited in ditches and drains and if possible place it back form where it came (i.e. in the field)

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Develop stable topsoil's by using bulky organic manures. But do not use excessive amounts of N. (See Farm Waste)

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Avoid surface compaction, rectify any problems before drilling

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Avoid fine seedbeds especially if prone to slaking as they will run together and seal the soil surface. 

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Using rotary implements can leave a fine tilth that has a high risk of slaking

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Do not roll seedbeds as this will lead to run off and erosion

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Set up tramlines after crops have emerged and do not use until the spring. This is often impractical so a shallow tine behind wheel will break up compacted soil

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Protect soil in winter by early sowing or use of cover crops

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Minimum or non inversion tillage will incorporate straw residues into the surface of the soil and help prevent erosion

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Row crops such as potatoes and sugar beet may be unsuitable on moderate and steep slopes. Soil walls can be used to bridge furrows across the slope (tied ridges) or pits along furrow bottoms to improve infiltration and reduce run off

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Work across slopes whenever possible, complex slope patterns may cause run off and formation of gullies.

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Take care when irrigating to avoid run off

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Careful selection of sites for outdoor pigs, taking into account, slope etc. preferably sites with grass cover

Pause for thought....List 3 reasons why we have seen an increase in severe erosion events in recent years?

 

If there is still a problem further action could be taken:

 
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Introduce grass into rotation, possibly on set aside areas

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Plant hedges, build new ditches, divert water away from vulnerable areas

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Create permanent strips of grass or rough vegetation as buffer zones to slow down run off and trap soil at critical places on a slope or at the bottom of a field

Controlling wind erosion:

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Grow rows of trees or plant hedges to provide protection for soil and crops grown on the sheltered side and to trap air-borne soil particles. The benefit will depend on the frequency and direction of the damaging winds

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Shelters should allow 30-50% of the wind to pass through. Protection of the soil reduces with distance from the shelter and does not exceed 20 times its height

 

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Use meteorological records of wind direction to decide placement of shelter belts

Extra protection for establishing crops:

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Consider cover or nurse crops such as winter rye or barley, as protection

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Kill off cover crop before the spring crop is drilled by cultivation or spraying. Kill off nurse crops early in life of main crop

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Surfaces can be stabilised via the use of mulches, organic manures sewage sludge etc. or synthetic stabilizers PVA (polyvinyl acetate) or PAM (polyacrylamides) can be sprayed onto sandy soils after drilling. (Only likely to be financially viable for high value crops)

Cultivation:

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Ploughing and leaving rough provides resistance to erosion 

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Plough and press lighter soils, preferably when moist and prior to sowing, drill at right angle without any further cultivation

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Uncultivated stubble provides protection against wind erosion and direct drilling can sometimes minimise erosion, but compacted surfaces will increase run off and lead to water erosion

The importance of the soil as a resource and issues associated with soil erosion are laid out in the soil action plan published in 2004.  Following the increased awareness of the importance of soil DEFRA are proposing a new soil strategy to be implemented in 2008.

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