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Compaction – prevention is better than cure

2 August 2011

Prevention is better than cure when it comes to soil compaction, CSF’s Anglia Regional Co-ordinator Nigel Simpson told growers at the recent East Midlands potato day.

A survey by Cambridge University Farm has shown that two thirds of fields growing crops had compacted soils. Combined with this, results from other research carried out on other fields has indicated an average yield loss of twenty per cent, of which only up to half can be recuperated through remediation, depending where the problem lies. This formed the basis of Nigel’s presentation.

Nigel went on to advise that the key to dealing with the issue is to plan ahead, so that problems can be minimised. The soil structure problem most likely to occur is compaction, although erosion and loss of organic matter are also common.

He also warned that soil problems are reflected in local water quality and may be a result of slope runoff linked to poor infiltration due to compaction, drainage losses of P, nitrates or pesticides or leaching of nitrates and pesticides, but they can all be linked to soil or timing issues.

To avoid compaction, growers were advised to minimise field traffic and stick to wheelings wherever possible.

He suggested that growers should ensure their soil structure is satisfactory by digging holes to a depth of about 50cm, 18 months and six months before planting potatoes. He also recommended that field layouts should be planned the previous autumn, or earlier if possible, and farmyard manure and fertiliser applied in dry conditions, with low ground pressure tyres being used for all field operations.

To enhance planting conditions Nigel advised that cultivation should be undertaken in the driest possible conditions, otherwise soils may smear rather than crack. If planting is to take place on heavy land, Nigel recommended the ground should be ploughed in the autumn or winter, when dry or frosted, to produce a rough seedbed.

“Establishing whether the soil is fit to plant is important too,” noted Nigel. “A quick way to check is to dig a 50cm hole. If the soil is plastic - that is it rolls in to a sausage 3-4mm thick without cracking - then the land is not fit to cultivate.”

Further advice included that where compaction is suspected, either in the previous crop or after potatoes, growers should use a spade to inspect areas where soil damage is likely. If a subsoiler is used, growers should aim for even loosening in dry soil across the profile, which can be checked using a spade.

“Once you know the depth of compaction, aim to cultivate 5cm below it. Lifting and cracking compacted soil helps to promote natural self- structuring,” he said.

Moreover, he emphasised that symptoms of poor soil structure include large, densely packed lumps of soil, with dull grey/brown faces, in the top soil just below plough depth. Platey layers are formed, with soil cracks travelling horizontally, with layers of wetness in the soil resulting in plant roots tending to travel down the cracks and the earthworm channels, rather than through the entire soil volume.

In conclusion, Nigel added that the Catchment Sensitive Farming Project’s aim is to improve water quality. “On slopes, we also need to see a reduction of sediment from run-off going into the water,” he said.

“Nitrates, phosphates and pesticides can all enter water with sediment. If you improve infiltration rates, you reduce the run-off issue. That gives a yield benefit, with less impact on surface water quality.”

The England Catchment Sensitive Farming Delivery Initiative (ECSFDI) is a partnership project between Defra, Environment Agency and Natural England which offers advice and support to farmers to reduce diffuse water pollution from agriculture.

The “Soil Management For Potatoes Guide” can be viewed and downloaded through the AHDB Potatoes On-line Publications Library.

For further information see http://www.defra.gov.uk/foodfarm/landmanage/water/csf/.

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