Best practice for managing the soil on outdoor units

Sarah Brown of the Environment Agency considers the outcomes from a recent project to develop soil management advice for outdoor pig farms

There’s no getting away from it, not only does being an outdoor pig farmer require a degree in nutrition, genetics and stockmanship, but also an MSc in soil management – coupled, of course, with an awful lot of enthusiasm.

In East Anglia, we have a significant proportion of the country’s outdoor pig units – largely located in Norfolk and Suffolk – and this seemed an ideal location to run a project, funded by the Environment Agency (EA) and delivered by ADAS. Our aim was to provide practical and effective help and advice to land managers within an outdoor pig rotation, whether that was for farmers’ cropping before and/or after pigs, or pig farmers themselves to help prevent diffuse pollution occurring, meet legislative requirements and save time and money where possible.

As we all know, the best sites for outdoor pig units are level, free-draining soils such as chalk and sand due to their porous nature. Herein lies the issue, as there’s real potential for direct run-off and infiltration of contaminated water, from fields housing pigs, into aquifers, rivers and streams. This contaminated water can contain nitrates (which leach through the soils) and phosphates (which move across land as soil erodes). This, in turn, has an adverse effect on the health of both surface waters and groundwaters for drinking water quality and the environmental status of the receiving waters.

Soil sediment deposited in watercourses also alters the river-bed composition by lowering bottom-dwelling animal numbers, damaging fish spawning areas (smothering their eggs), reducing navigable areas, and carrying contaminants and nutrients that degrade water quality. High nutrient levels within the river system encourage algal growth in the watercourses, decreasing the diversity of aquatic plant life. As the algae plants die and decompose, the organisms breaking down the high levels of organic matter deplete the water of oxygen, causing the death of other aquatic life, such as fish.

Industry workshops
The project centred around two well-attended evening workshops for arable and pig farmers, landowners and industry representatives that followed visits to two outdoor pig farms in the region. These workshops included in-depth discussions on three core topics: managing soils sustainably; managing nutrients well; and managing pigs efficiently and effectively.

Our aim was for workshops that would provide practical advice and good ideas for everyone involved in an outdoor pig rotation based on real life farms where land is managed for both arable and outdoor pig enterprises.

The two events revealed a number of important considerations for those involved in outdoor pig production. These included:

Very often the nutrient availability to the following crop after pigs was not taken into consideration. You need to take into account the Soil Nitrogen Supply following pigs and the results of regular soil sampling for phosphorus, potassium and magnesium. Then, use information sources such as the Defra Fertiliser Manual (RB209) or the free nutrient planning software PLANET to guide you on subsequent fertiliser requirements. Don’t ignore the levels of nutrients available to the next crop following a rotation of outdoor pigs; it doesn’t make good environmental sense, and you could be wasting good money on unnecessary fertiliser.

Capping (the formation of a hard crust on the soil surface following rainfall on light soils) was an issue on many units. This cap decreases the infiltration of water and increases run-off that can carry sediment and nutrients into water. You can use shallow tines or discs to break up capped soils, particularly in empty paddocks, and keep the soil surface as rough as possible to prevent a cap forming.

Compaction was also an issue on many units. Both machinery and livestock will compress the soil, removing air pores and creating a dense layer that decreases infiltration of water and increases the risk of run-off.

Use soil pits before and after outdoor pigs. This will help you to identify any structural issues that could lead to run-off, and allow remedial action to be take if necessary. Remove shallow compaction through cultivation and remove deep compaction by subsoiling, but remember soil moisture and depth is critical. If too deep and/or too wet, the subsoiler will smear rather than shatter the soil, unnecessary fuel and horsepower will be required and sub soiling will need to be completed at a later date when the soil is in a friable state. If too shallow, then the subsoiler will not create any lift to the layer and can just “skim” over the layer of compaction. If the soil is too dry, then the draught requirement will be too high and again unnecessary fuel and horsepower will be required to complete the job.

The importance of soil organic matter should never be underestimated. Organic matter is your reservoir for nutrients and water; lose this and the soil structure and potential productivity will suffer.

Select sites very carefully for outdoor pigs. Consider access routes, soil type, proximity to water and proximity to roads and slopes that could potentially channel run-off to watercourses some distance away from the site. Understand the risks presented by the soil type, weather and landscape features of a site, combined with the proposed cropping and stocking rotation. Find out the previous cropping and cultivations, and use soils pits to assess soil structure so that any issues can be addressed before pigs enter the site. It is much easier to prevent a problem from occurring in the first place than to rectify it after severe run-off or erosion.

Consider access routes for machinery on the site. Remember that the first pass by a machine accounts for 50% of the compaction, so stick to designated routes that don’t channel water and that are well protected by grass buffer strips. Carefully consider tyre choice and axle loading to minimise compaction.

Avoid bare land before and after pigs. If possible establish a grass sward before pigs and consider cover crops after pigs before the next crop, if the rotation allows. These options will prevent soil movement, capture nitrogen that would otherwise be leached down through the soil, increase organic matter levels and improve soil structure.

More advice
It was also established that producers want more free one-to-one advice on soil management. Options here include contacting your local Catchment Sensitive Farming (CSF) officer to organise a free confidential advisory visit. These can cover the topics of your choice including specialist visits such as nutrient planning, soil husbandry, pesticide filling areas and farm infrastructure, or you may prefer a whole farm appraisal to have an overall health check of the farm. To contact Natural England’s CSF team, call 03000 601111. Alternatively, you can speak to your local EA officer on 08708 506506.

There are plenty of other sources of information on land management for outdoor pigs that can be found on both the BPEX website ( and on the website. In particular, the EA publication Think Soils is a useful practical guide to using soil pits to assess structure and reduce run-off and erosion. It can be found at:

BPEX was involved in this project from the start and has subsequently released its own publication, Good Soil Management Practice – A Guide for Outdoor Pig Keeping. This is available to download from the BPEX website or free copies can be ordered by calling 02476 478792.

Finally, if you want to find out what’s happening in environmental terms around your farm, you can visit the What’s in your Backyard for Farmers (WIYBY) website that shows you the environmental features, land designations and any known water quality issues in your area. It’s at:

Get Our E-Newsletter - Pig World's best stories in your in-box twice a week
Will be used in accordance with our Privacy Policy

About The Author