Visual Evaluation of Soil Structure (VESS)

This simple test (original guidelines developed by SRUC) assesses soil structure based on the appearance and feel of soil dug out with a spade. Here, structure is a shorthand for soil health based on how aggregated (the crumb structure that healthy soil naturally has) the soil is. Aggregation is a product of biological action, normally the result of microbes gluing soil particles together into larger clumps (or aggregates). That is why true biological aggregates will have a rounded (or crumb-like) appearance, sort of like cottage cheese but on a much smaller scale.

The scale ranges from 1 – very good structure, to 5 – poor structure. For each spade-full you are encouraged to do two VESS readings, one for the top layer of soil, and another for the soil below, as well as measure the depth of each. Usually the top layer has a higher score, and as the soil improves over time it will get deeper and deeper, so it’s important to record the depth.

Don’t get too hung up trying to get the exact score. You will get quicker with practice. And the more repetitions in the same field the more that the values average out. So individual variations or “errors” are ironed out.

Equipment:

  • Digging spade
  • Tray/bin bag
  • VESS score chart (initially)
  • Pocket knife/trowel (optional)
  • Ruler

Doing test:

  1. Dig out 3 sides of a square as wide as your spade, and dig down about 20 cm if possible.
  2. Leverage the soil block out of the ground, (one side undisturbed by the spade) place on tray/bin bag.
  3. Take a photo of the undisturbed side of the block.
  4. Look for a difference in colour and consistency of the soil, near the surface. This is the  top (turf) layer of the soil. The rest of the soil is the bottom layer.
  5. Measure the depth of the turf layer, record in the app.
  6. Begin to break down the soil gently in your fingers. Until you have clumps of soil about 1.5-2cm in your hand
  7. Follow the VESS scoring guidelines here. The main questions are: Are the clumps angular? Do they have roots running through them? How easy is it to break them down? How porous are they? With gentle pressure breaking them down what size are most of the clumps?
  8. Record the VESS score in the app.

Record:

  • Photo of the soil profile
  • Depth of the top/turf layer soil in cm.
  • VESS score for the soil (1-5).

Tip:

When you are doing your first VESS tests, take a number of samples from the different fields and put them in trays. Bring them back to the office for scoring so that you’ll be able to compare between the different soils side by side. This helps to better understand the differences between soil scores as described on the VESS diagram. So, for instance if you score one soil a ‘3’, and you’re happy with it, then you can work out whether the remaining soils are more or less than that, by asking the question “is it better or worse than soil I scored 3?”, then refer back to the VESS diagram and see if the description makes sense for that score for that soil.

Resources:

The VESS test was developed by Scotland Rural College (SRUC)