Slake test

The slake (wet aggregate stability) test scores how well your soil structure holds together in water.

Healthy soil has good organic matter content and is full of microorganisms that secrete glues which create the aggregated crumb structure we want to see. When aggregates with a good soil structure held together by organic matter and biological glues are submerged in water they stay together.

When aggregates with a poor soil structure held together by compaction are submerged in water they fall apart.

What to record

Record Slake Score

0: Dissolves into single grains – lump collapses completely, as soil is too unstable to isolate aggregates.

0.5: Soil slumps into pyramid – lump collapses into a cone of <2mm grains, water is cloudy.

1: Breaks into angular pieces – the lump breaks up into larger angular pieces, indicating a loose, granular surface layer.

1.5: Stays mainly intact – lump edges crumble slightly but remains largely intact.

2: Lump intact – lump remains completely intact and the water is clear, indicating your soil is resistant to erosion

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, gently breaking 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 1-5mm pieces of soil from each sample location and leave them to dry overnight. They may need another day or two to dry completely!

4. When they are completely dry, arrange the three pieces from a single sample location onto the sieve, and fully immerse them in the bowl of water. A light coloured bowl as a background will make them easier to observe under water.

5. Set a stopwatch for 5 minutes, & observe the soil underwater. Score the behaviour of the soil from 0-2 using chart above. The soil may breakdown and remain in the sieve. This is still considered breakdown of the original structure.

6. You may like to take another sample in an uncultivated part of the farm, e.g. woodland or headland, for a comparison to assess the effect of field management on aggregate stability.


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