Slake Test (Scores: 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.
- 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.
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.
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