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Remove soil compaction
The guidance on this page is for SFI pilot participants only. Please visit GOV.UK for the official Sustainable Farming Incentive scheme guidance.
Find out how land managers can improve soil health and crop growth by using machinery and biological processes to reduce soil compaction.
If you’re completing this action as part of the Sustainable Farming Incentive pilot, how you do it is up to you.
The advice on this page can help you get better environmental and business benefits, but you do not have to follow it to get paid.
About soil compaction
Livestock or machinery used in agriculture, horticulture and forestry can compact soil. Compaction happens when soil is compressed. This leads to:
- loss of soil structure
- a decrease in soil porosity (the gaps in soil that are normally free for air and water)
- less water movement through the soil
- higher bulk density (the dry weight of soil in a given volume)
Soil is at most risk of compaction when it’s wet, usually in late autumn and winter.
Benefits of reducing soil compaction
Environmental and business benefits include:
- more efficient crop establishment and nitrogen uptake
- easier harvesting
- less risk of machinery and animals damaging the soil
- better flood and drought resilience
- cleaner drinking and bathing waters due to less runoff and erosion
- less ammonia in the air, as nitrogen fertiliser and organic manures applied to compacted ground emit more gas
- less greenhouse gas emissions
Land prone to soil compaction
Cultivated land is normally compacted by machinery in high-traffic areas like:
- tramlines
- headlands
- gateways and surrounding areas
Heavier machinery can cause widespread subsoil compaction down to 60cm depth, even if you spread the load with low pressure tyres. If subsoil conditions are wet, deeper compaction will remain even if you loosen the topsoil. You should remove this deeper compaction when the subsoil is drier.
Compaction can also occur:
- in fields where you store manure before spreading
- as a surface crust or cap, most likely after heavy rain on bare soil with high sand or silt levels
- where organic matter levels and earthworm numbers are low
Livestock can cause compaction by trampling (poaching) wet ground, especially around high activity areas like gateways, drinking troughs and feeders.
In wetter soils, cattle cause hollows 10cm to 12cm deep. This can form an almost continuous layer of grey waterlogged soil. Sheep are less likely to break the soil surface, but in high numbers can produce a solid compaction layer 2cm to 6cm deep over a wide area.
Identify soil compaction
Look at field conditions, especially during and after rain. You’re likely to see:
- areas of standing water
- surface water runoff and erosion
On cultivated land you can also assess crop condition. Look for:
- poor growth of different crops, over successive seasons, in the same area of a field
- uneven crop growth across a field associated with tramlines, headlands or gateways
- a smooth surface crust or cap
Signs that grassland is compacted include:
- poached ground, particularly around feeders, drinkers and gateways
- uneven grass growth, over successive seasons, in the same area of a field
- an increase in rushes and problem weeds, like docks and thistles
Read the thinksoils manual to find out more about identifying grassland compaction.
Dig soil pits
You can identify compacted soil using soil pits. Dig pits on cultivated land once a crop has been removed and before planting the next crop. You can assess compaction at any time of year, but it’s best during and after rain and not when soil is very dry.
To do this:
- Dig a small pit about 50cm square and at least 40cm deep (60cm to check for deeper compaction problems).
- Use a spade to remove an intact block of soil a spade width square and a spade length deep.
- Lay this block on its side and use both hands to pull the block vertically apart.
- Examine this block and the sides of each soil pit for signs of compaction.
- Dig extra pits to assess depth variation and thickness of a compacted layer (often called a ‘plough pan’ in arable soils).
Compacted soil will have:
- a blocky, hard to break structure
- shallow, horizontal roots
- few or no earthworms
- a greyish soil colour
- a stale smell
Use soil penetrometers
You can use soil penetrometers with soil pits. Penetrometers are quick to use over large areas. They detect how much pressure you need to push a metal rod through soil.
Results can be inaccurate if the tip hits lumps, stones or cracks. This could mean you try to remove compaction at the wrong depth, so a soil pit will confirm if you need to loosen with machinery.
How to reduce soil compaction
The depth and extent of compaction will determine how best to loosen the soil. You can use machinery or natural biological processes.
If you use machinery to reduce soil compaction, do not use it:
- over known buried or surface historic features
- on semi-natural or natural habitats
- deeper than the shallowest field drain
Wait until your soil is dry enough for machinery to break up (shatter) the compacted layer. Late summer or early autumn can be a good time.
Avoid using machinery on wet soils, especially if prone to compaction, like clay, clay loams and silty clay loams. They are likely to lose structure and make existing compaction worse.
You can use cover crops or companion crops after loosening the soil with machinery to help improve its structure.
Reduce soil compaction in grassland
Remove livestock and machinery when the ground is wet to help surface compaction to recover naturally
To loosen soil with machinery you can use a soil aerator or pasture slitter. A rotor, fitted with radial blades or spikes, opens up the soil surface down to 15cm depth. For deeper compaction between 15cm to 35cm depth, use a grassland subsoiler or sward lifter.
If you have wet, clay-based land, the cause could be poor drainage rather than compaction. You may need to renew existing field drains.
Check if you can get funding for new soil compaction removal equipment.
Reduce soil compaction in tillage land
To avoid surface compaction use vegetation or crop residues to provide cover. Add organic matter to help strengthen the soil.
Treat deeper compaction with a subsoiler to create vertical cracks in the soil profile. Use after harvesting as:
- soils should be at their driest, making them easier to shatter
- you’ll avoid damaging crop roots
Subsoilers
Subsoilers, also known as flatlifters or paraploughs, use straight or forward inclined vertical legs to lift and break up a compacted layer. You can attach chisel points or wings to the legs for extra shatter.
Operations below the critical depth will increase compaction, so it’s important to set the working depth correctly. Critical depth typically occurs at 6 times the width of a subsoiler leg. For example, if the foot of a leg is 8cm wide it will have a critical depth of 48cm.
On a winged subsoiler, set the tines at 2 or 2.5 times the tine depth. For example, to subsoil at 30cm depth the subsoiler tines should be 60cm to 75cm apart.
Reduce soil compaction with natural biological processes
Plant roots and earthworms naturally reduce compaction, which:
- allows soil structure to recover (provided the soil does not compact again)
- is typically limited to the top 5cm of soil, but can reduce deeper compaction
- usually works on lightly compacted soils (a thin compacted layer less than 10cm thick), where there are roots and earthworms
Prevent compaction from happening again
Soils loosened by machinery can become compacted again within a year. To prevent this:
- let the ground recover after loosening to prolong results
- undersow or sow a cover crop to stabilise soil after harvest
- have full vegetation cover, ideally with deep rooting plants
- establish crops in early autumn during dry conditions
To improve soil structure you can add extra organic matter, or add calcium to medium and heavy soils.
Move livestock regularly and use well-drained fields if you overwinter animals. Fencing can help manage livestock numbers near water.
To minimise damage from machinery you can use:
- min-till or no-till farming
- controlled traffic farming
- better maize management
- less intensive management next to water
How to tell if your soils are less compacted
Crops grown where there’s no soil compaction have more uniform establishment and growth, as roots can grow freely. You’ll see less drought stress, where dry soils reduce plants’ ability to absorb water, as roots can penetrate deep enough to access water.
You’ll see:
- reduced runoff and erosion, with less sediment seen in tracks, ditches and on nearby roads
- clearer water in nearby watercourses, with no signs of excess plant growth
- fewer occasions where downstream homes, properties and roads flood
You will not see:
- standing water or soil ruts, as water can get into the soil more quickly
- compaction by machinery, as better-structured soils should need less work
