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Soils 2: Drainage

Course: Sustainable Soils | Last Updates: 26th November 2015

Alice Midmer
Project coordinator
Biography >>

Grey soil colours due to reduced forms of manganese and iron in the topsoil indicate the soil is waterlogged and deficient of oxygen for long periods.
This poor aeration leads to a build-up of carbon dioxide and methane, and reduces the ability of plants to take up oxygen, water and nutrients, particularly nitrogen, phosphorus and potassium.
Poor aeration also slows the breakdown of organic residues, and can induce chemical reactions toxic to plant roots.

What to look for

The colour of the soil is a useful indication of soil drainage, aeration, soil wetness from late autumn to early spring, and soil damage. A warm, uniform, brown and black soil is a sign of good drainage but grey mottled soil is an indicator of potential drainage issues.

Influence of soil type

Soil type can have a large influence on the drainage capabilities of a soil. Subsoil texture can also play an important part.
Heavy clays often struggle to drain water away efficiently especially if they are compacted.
By contrast sandy soils drain very quickly with all reference farms with sand soils scoring the maximum 2 for drainage, while other soil types were more variable.
However, as a result of easy drainage, sandy soils can struggle with water holding capacity which is a problem for some farmers in drier weather.

Improving drainage

Despite variations in soil type, there are a number of measures that can help improve drainage on all soil types.
Adjusting soil management practices can have a large influence on the soil quality and can particularly influence the long term sustainability of your soil.
Leaf carried out on farm soil interviews with a wide variety of farmers across the UK.
Despite a large variety of soil types, many had adjusted their soil techniques in the same way to improve their soil quality.
The following measures were used particularly to improve drainage.
Further information on the farm specific implication of these changes can be found in farm case studies:

Artificial drainage

Ensure any artificial drainage is properly maintained and repaired regularly.
If previous drainage is insufficient consider the full benefits of introducing or replacing the drainage network.

Cover crops

Deep rooting cover crops can help improve the drainage capabilities of the soil through loosening the subsoil.
Ground cover with shallow rooting plants to hold soil in place on steep or exposed land helps to minimise erosion. Cover crops can also help to suppress weeds – as a soil sterilant when chopped and cultivated in to the soil which release chemicals. And cover crops are now part of the CAP greening requirements.

Biological improvement

Burrowing earthworms are an important part of a well-drained soil, especially in minimum tilled land. Under minimum tillage, earthworm populations increase and are often relied upon to ensure sufficient drainage.
For further information see Hampden Bottom Farm, College Farms and High Meadow Farm.


A good structure and minimal compaction are important constituents of good drainage.
If drainage is causing a problem on your land, ensure it isn’t rooted in poor soil structure or compaction.

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