2.0 Visual Evaluation of Soil Structure (VESS)

This test (original guidelines developed by SRUC) assesses soil structure based on the appearance and feel of soil dug out with a spade.

In this test you observe and record how aggregated the soil structure is (aggregation is the crumb structure naturally occurs in healthy soil).

The scoring 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 scores better, and as the soil improves over time the top layer will get deeper, so it’s important to record top depth.

Aggregation is a product of biological action, normally the result of microbes gluing soil particles together into larger clumps (called aggregates). True biological aggregates have a rounded (crumb-like) appearance, like cottage cheese but on a smaller scale.

What to record

VESS score (top)

VESS depth (top)

VESS score (bottom)

VESS depth (bottom)

Equipment

Digging spade

Tray / bin bag

VESS score chart (initially)

Pocket knife / trowel

Ruler

How to do the test

1. Locate your chosen sample site – you can use the GPS mapping feature on the app to do this if you’ve recorded the sample locations previously.

2. Dig out 3 sides of a square as wide as your spade, and dig down about 20 cm if possible.

3. Leverage the soil block out of the ground, (leaving one side undisturbed by the spade) and place on tray/bin bag.

4. Take a photo of the undisturbed side of the block.

5. 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 will be the bottom layer.

6. Measure the depth of the turf layer, record in the app.

7. Looking just at soil in this layer, begin to break it down gently in your fingers. Until you have clumps of soil about 1.5-2cm in your hand

8. 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?

9. Record the VESS score in the app.

10. Repeat steps 5-8 for the bottom soil sample.

Don’t get too hung up trying to get the exact score. You will get quicker and understand the scoring better with practice.

Read this article to find out how many times to do the VESS test in each field.