2.2 Slake Test

Assess the stability of soil aggregates in water (the Slake test). Shows the integrity of the soil crumb structure. The slower the soil breaks up, the better; this indicates a high degree of organic matter which holds the soil together.

This method is based on the one used by our Soilmentor soil health expert Jenni Dungait in her recent research doing on-farm soil testing with farmers in the South West of UK.

What to record

Record 0-8 Slake Score (see chart below)

Make notes: Anything interesting you’ve noticed!



A smartphone (with Sectormentor downloaded)


Bags to carry soil sample (carrier bags will do!)

Permanent marker

Kitchen sieve

Bowl of cold water

Stop watch

How to do the test

1. Choose a day when the soil isn’t waterlogged and hasn’t been recently cultivated, and head to your sample block / location you’re interested in testing in the soil.

2. Dig about 15cm into the soil with your spade, and gently break the soil apart. Take a handful of soil and put it in your collection bag to be taken back for testing. Repeat this step wherever you want to take soil samples / for however many samples you have chosen to measure!

3. Back at the office, select three 1cm pieces of soil from each sample location and leave them to dry overnight.

4. The next day, arrange the 3 pieces from one sample location onto the sieve, and fully immerse them in the bowl of water.

5. Set the stopwatch for 1 minute, and observe the pieces of soil over this time frame. Give the soil samples a score from 1-3 using the top of the chart below after 1 minute has passed. The soil may breakdown and remain in the sieve. This is still considered breakdown of the original structure – see the video below if you’d like help scoring!

6.¬† If the pieces scored 0 – 2, record this score in Sectormentor and you can finish your testing at this stage. If the pieces scored 3 (more than 50% of the soil pieces are intact), move on to the next part of the test…

7. Slowly raise the sieve up and down 5 times, so that the surface of water just touches the tops of the soil pieces each time, and score the behaviour of the pieces from 3-8 using the chart below. Record this score in the app and take a photo for future reference!

8. You should now have a Slake score from 0 – 8, with 0 being unstable, and 8 being extremely stable! You may want to repeat this in areas that are under different management in your vineyard to get interesting soil health comparisons…


This methodology is based on the method developed in the following research:

Collier SM, Bearder T, Dungait JAJ. (in preparation) Exploring the potential for soil organic carbon management in agricultural soils: Case studies from Tamer Valley, Devon, and South Cotswolds, Gloucestershire, UK. Soil Use and Management

Adapted from USDA ARS On Farm Soil Monitoring

This scoring is based very closely on this table from the USDA aggregate scoring

Table 1: Aggregate stability scoring criteria