Using visual soil assessment

Working together a spade, your hands and eyes are the most important tool for soil management.

The GRASS visual soil assessment method has been developed to provide a quick but systematic way of assessing soils visually to provide useful information to guide management. Get the pocket book

Carry out assessments when the soil is moist if the soil is too dry or too wet it is difficult to distinguish signs of poor soil structure.

Assessing the soil

 

Where and how to look at soil structure

Just one assessment per field isn’t enough, you should investigate 3-4 sites; allow around 45 minutes for your investigation depending on the size of the field.

You might want to start by getting familiar with signs of soil structure damage in your soil type  -  so dig in an area where you know there may be a problem (e.g. a gateway)

Surface assessment of the sward can help to identify the extent of potentially damaged areas and help to target investigation and then to zone the field for management options

Watch out for:

  • Surface poaching
  • Evident wheelings
  • Weeds in the sward
  • Poor sward quality
  • Dung and/or slurry on the surface for months
  • Bare ground
  • Water ponding on the surface

 

To assess soil, you will need to extract an undisturbed soil block

  • Dig out one spade-sized block of soil (depth approx. 30cm) by cutting down on three sides and then levering the block out to leave one side undisturbed
  • Lay soil block on a plastic sheet or tray

Once you have a soil block,

  • Gently open soil block like a book to break it up
  • If the structure is uniform – assess the block as a whole
  • If there are two or more horizontal layers of differing structure identify the layer with the poorest structure 'limiting layer' and assess this.

Assessing the soil

When you assess soil, you are looking out for:

  • Rooting patterns  – roots will extend to 30cm plus in healthy, well structured soil
  • Soil aggregates – the size and shape of the soil aggregates is a key indicator of soil damage.  In well structured soils there will be plenty of small aggregates (granules and crumbs) with rounded edges.  Larger aggregates with sharp edges are a sign of compaction.
  • Cracks and pores – ideally there should be vertical channels between the soil aggregates to allow free movement of water, air and nutrients
  • Earthworms – there should be evidence of earthworms and their activity (burrows, casts) in the section removed
  • Colour – topsoil rich in organic matter will be dark. Rusty, grey mottled soils indicate poor drainage and previous waterlogging
  • Smell – if water lies trapped in the soil for any length of time, the air-less condition prevents breakdown of organic matter and manures.  A foul-smelling dead layer of debris may form

In the field, use the GRASS field guide to help allocate a score

Assess Field guide here[VAC6] 

Environment Agency   

The Thinksoils Manual – aimed at farmers and advisers to help them recognise problems with soil erosion and runoff from agricultural land. It is a useful and practical guide to soil assessment, and helps identify high risk areas. Download Thinksoils manual

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