Soil health indicator: get insight into how biological activity affects your soil structure with the slake test score of 0-8
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.
We had feedback from some farmers that the method we used previously with scores of 1-3 didn’t have enough increments. This new testing method is based on that used by our soil health expert Jenni Dungait in her recent research doing on-farm soil testing with farmers in the South West.
PLEASE NOTE: THE 0-8 SCALE IS EXPLAINED BELOW
- Small bags and permanent marker (to take labelled soil samples back to office to dry overnight)
Back in the office:
- Sieve with a small mesh (2 mm, one that you would use for sifting flour in the kitchen)
- Bowl of cold water
- Stop watch
- Choose a day when the soil is not waterlogged and it has not been recently cultivated.
- 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.
- Insert your spade to about 15 cm depth into the soil. Dig up the soil and gently break it apart to release pieces of soil.
- Collect a fist-sized sample of soil put in small labelled bag to take back.
- Back at the office: select three 1cm-sized lumps of soil from the bag and leave them to dry overnight.
- Next day: Arrange pieces of soil on the sieve and fully immerse into water until the lip of the sieve is reached.
- Observe the pieces under water for 1 minute. Score the behaviour of the pieces from 0 – 3, see Results section below.
- If the pieces scored 0, 1 or 2, record this score. Record this in the app and take a photo. The test is over.
- If the pieces of soil scored 3 (more than 50% of the original soil piece remains is left on the sieve), move on to the next part of the test.
- Slowly raise the sieve up and down 5 times (with approximately 1 second transit time up and 1 second down) so that the surface of the water just touches the top of the aggregate. Score the behaviour of the aggregates from 3 to 8. Record this in the app and take a photo.
- You will have a score from 0 (unstable) to 8 (extremely stable).
- You may like to take another sample in an long-term uncultivated part of the farm, e.g. woodland, for a good comparison to assess the effect of field management on aggregate stability.
What to record in the Soilmentor app:
A score of 0-8 where,
0:Unstable, no aggregates – soil too unstable to isolate aggregates.
1:<5 secs 50% structure lost – 50% structural integrity is lost within 5 seconds.
2:<30 secs 50% structure lost – 50% structural integrity is lost within 5-30 seconds.
3:(Sieve)<10% remains – 50% structural integrity is lost within 30-60 seconds. If after 60 seconds 50% or more of the original piece remains in tact, then you perform the sieving. If after sieving less than 10% remains then it remains a score of 3.
4:(Sieve)10-25% remains – 10-25% of the original structure remains intact after sieving.
5:(Sieve)25-50% remains – 25-50% of the original structure remains intact after sieving.
6:(Sieve)50-75% remains – 50-75% of the original structure remains intact after sieving.
7:(Sieve)75-90% remains – 75-90% of the original structure remains intact after sieving.
8:(Sieve)>90% remains – more than 90% of the original structure remains intact after sieving and the water is totally clear.
Don’t forget to take photos too!
Read this article to find out how many times to do the slake test for each field.
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
This scoring is based very closely on this table from the USDA aggregate scoring
Table 1: Aggregate stability scoring criteria