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Soils: wind erosion

Course: Soil Management | Last Updates: 7th October 2015

 
Fraser Milne
Independent Consultant
Siguna Consultancy
Biography >>
FADS2BASIS2

What is wind erosion?

Over time, or in very strong gusts, the movement of soil particles by wind can lead to a substantial movement of soil both within a field and over a larger area of countryside. Sand dunes, or soil deposits on roads in spring time after strong equinox winds are common examples.

How is it caused?

When the soil is dry, high air velocity close to the ground causes small unattached soil particles to become airborne.  These are then carried until the air velocity reduces at which point they can no longer be suspended in the air. This tends to segregate deposits into soil particles of a similar size.

Why is it a problem?

Wind erosion

There are problems associated with both soil deposits and where they have come from. Wind storms can easily fill in potato ridges, for example, leaving another area with uncovered tubers.

Young plants are vulnerable to damage from sand-blasting during storms. And soil can be deposited at a field edge, the side of roads, or at field gateways. As well as causing a public nuisance, these deposits need to be shifted.

What soil types and cropping regimes are vulnerable?

Areas of the countryside that have frequent high winds or gusts, notably coastal areas, are most at risk. And natural features like hills or blocks of trees can cause a wind-funnelling effect leading to local problems. Buildings can also cause this.

Fields left cultivated with no crop cover are vulnerable, especially soils with low cohesive properties, such as sands. Some light loam soils are also at risk since particles have a low weight to surface area ratio.

Crops that require a very fine seedbed, such as small seed crops, are most at risk. Damage can be worse if the crop is slow to reach ground cover.

What can I do to reduce erosion?

Fleece

Firstly identify the direction and the time of year when the problem is of most concern. Often the wind blowing from a certain direction, rather than from the most frequent one, can cause the biggest problems, and this can be seasonal.

Reduce large open areas by strategic planting of hedges and shelterbelts. Aim to reduce wind velocity, rather than completely block it, as a solid shelterbelt can cause turbulence on the leeward side, leading to further problems.

Increasing the organic matter content of the soil is a long-term measure that will help improve soil structure and reduce erosion. In the short term, try not to over-cultivate.

Establish ground cover quickly and avoid leaving land cultivated and bare for any length of time. This may mean planting barrier or cover crops between the target crops.

Modern techniques using plastic fleeces and soil stickers can also work. Irrigating the soil can help but wind itself can hamper the operation, and the soil tends to dry out very quickly.

Why has Tim Pratt's system worked?

The farm is managing the wind erosion problem well using natural controls which capitalise on the farm’s environmental assets. These are combined with agronomic factors, such as fleece, floating plastic and using soil stickers, and protective crops planted when soils are most vulnerable.

Case study

Tim Pratt – Woodbridge, Suffolk

tim-pratt-holding-soil-in-his-handsWander around the wildlife-rich lagoons and whispering belts of fir trees on Tim Pratt’s Suffolk farm and you’d scarcely believe the primary aim of these environmental assets is to maximise production.

The 20ha of lagoons are irrigation reservoirs for the 340-450 ha of potatoes, onions, carrots, sweet corn and sugar beet he grows at Wantisden Hall Farm for JH Kemball and Son on the coast near Woodbridge.

The belts of trees are the number one defence against one of the farm’s biggest enemies: wind.

“There are times of year when the wind picks up sand particles and can just cut off a young plant. And before you know it you have a six-foot bank of sand at the edge of your field,” explains Mr Pratt.

The soil type is a very coarse sand. “It’s just like being on a beach. We have something of a micro-climate so we can go for the early, niche markets. But it does like to blow, especially in March and April, and you have to manage that.”

The fir trees were established about 30 years ago, when the land was reclaimed from heathland. These are now being carefully thinned, with replacement native deciduous species planted where appropriate.

Pond


The farm has also recently established over four miles of new hedgerows under the Countryside Stewardship Scheme. “The aim has been to diffuse strong winds and ensure there aren’t long tracts of open ground where the wind can gather pace,” notes Mr Pratt.

Planting and cropping is also adapted to suit market and soils – a dual benefit that’s behind many management decisions made at Wantisden.

Carrots are planted in January and covered until April. The poly-cover protects the bare soil and the crop is among the first to be lifted in the country, cashing in on a lucrative early market.

Onion sets, rather than seeds, are planted two months early on more vulnerable fields, so that by the time the strong March winds arrive there are more than two true leaves to withstand a sand-blasting.

Potatoes are also planted early and harvest starts in June, with crops sold loose-skinned at a premium to major multiples. With no defoliation necessary, ground is not left vulnerable to erosion and tuber-greening.

Soil stickers, such as Emupol, are applied to high-risk, delicate vegetable crops. This contractor operation costs about £200/ha.
Cover crops are another new introduction. The farm is working with the Environment Agency trialling a range of crops such as clovers, grasses, vetches and mustard. These are broadcast in early summer after a vegetable crop, then sprayed off and incorporated the following spring.

“The cover crop has to be simple and involve as little work as possible while bringing the most benefits.

It’s a slow process, but we’re beginning to see that it builds nutrient and organic matter content and boosts beneficial insects.”
While there’s a business benefit in every measure Mr Pratt implements, he’s quick to promote the spin-offs at Wantisden, a LEAF demonstration farm.

“We regularly host school visits and farm walks. Yes, this is a highly productive farm, but people appreciate the bigger picture we’re achieving here.”

Golden Rules

  • Plan your cropping – use your Soil Management Plan to tailor crop, planting and harvesting to suit the site
  • Investigate cover crops – their benefits are long-term, but make sure the cover crop fits well with your target crop
  • Plant trees – make the most of establishment grants, plant native species and aim to diffuse wind, not block it.

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