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Outdoor production now accounts for more than 30% of the national sow herd. The industry has developed through consumer recognition of its animal welfare credentials, leading to a strong demand for outdoor reared products. This industry now forms an important part of many arable and root crop rotations and is seen as a break crop and contributor of valuable plant nutrients to the soil. A soil type which is naturally free-draining is preferred such as sandy, light silty and chalky soils. Unfortunately such soils are commonly weakly structured and prone to damage by trampling underfoot. Producers recognise their responsibilities for soil management and protection, This has resulted in many changes in recent years, including laying out sites considering natural slopes and surface water flow paths, and the use of set-a-side as buffer strips around field margins. The pig industry was the first to develop and adopt its own soil management plan to prevent problems arising and demonstrate responsibility.
Organic matter
Outdoor pigs contribute important plant nutrients to the soil. Most sites are occupied by pigs for a two-year period, however a significant proportion of the nitrogen deposited can be released in the second year, unless good crop cover can be retained. Establishing grass cover in advance of the pigs arriving on site, perhaps using one year set-a-side, permits the cover to be largely retained for the two years. The cover reduces nitrate leaching and in some instances phosphate losses as well as helping to reduce the likelihood of soil erosion which is the main cause of phosphorus loss. In common with other livestock enterprises, the manure which pigs produce helps to maintain soil organic matter content.
BPEX Soil management plan for outdoor pig keepers  (127kb)
Yield/Quality
Slumping and Capping
Waterlogging
Poaching
Compaction
Wind Erosion
Water Erosion
Grass needs to be managed to maintain good cover, this can include rotating pigs, topping and sub-soiling to alleviate localised compaction.
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The lighter soil types most commonly associated with outdoor pig keeping are prone to slumping and capping; cover reduces the risk of this.
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Soils where the whole root zone is prone to water-logging are not ideally suited to outdoor pig keeping and tend to be avoided by pig farmers. Where water-logging is likely, then management plans need to take this into account and good practice followed.
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Poaching of wet soils can be a significant problem faced by producers. Moving houses or feeding points, if possible, can reduce this. Other techniques may include fencing off oblique corners in radial pens so that the pigs cannot congregate in the corner.
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Both pigs and the machinery used for feeding and moving them can cause soil compaction. The use of carefully planned permanent roadways can however limit vehicle compaction. Surface ponding of water is often a visible sign of soil compaction and, when soil conditions permit, sub-soiling can provide a solution. Some producers walk pigs between enclosures to avoid vehicles travelling on compaction prone soils. Soil cover crops again can reduce the level of compaction. Soil compaction coupled with sloping ground can be a major cause of soil loss from outdoor pig fields during prolonged wet conditions.
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The light soils used for pig keeping can be prone to wind blow. The best way of minimising the risk of wind erosion is by maintaining a good cover crop such as grass.
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Where pigs are kept on slopes, surface runoff and erosion can occur. As the ideal soil type for outdoor pigs is free draining, and herds are predominantly sited on light sandy soils, sloping sites with sandy soil, particularly where the soil organic matter content is low, are at high risk from erosion. Furthermore, the excreta deposited in fields accumulates a large amount of nitrogen and phosphorus within the soil surface which is at risk of entering sensitive sites such as watercourses and roads if erosion occurs. Farmers are well aware of this significant potential problem and are encouraged to compile and implement a soil management plan to identify the areas at greatest risk and take mitigating action.
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Further information can be found on the BPEX website at http://www.bpex.org/technical/tech2/environ/soil.asp
Controlling soil erosion: an advisory leaflet for preventing erosion by outdoor pigs, 2001 (PB5820C)
Controlling soil erosion: incorporating former advisory leaflets on grazing livestock, wind, outdoor pigs and the uplands, 2005
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