Measuring soil stablity - sieving soil!

 A few weeks ago, Sarah and I measured the soil stability of each of our experimental trays. That meant that we collected a soil aggregate (a very small clump of soil particles) very carefully from each tray. Each soil aggregate was placed in a sieve basket. I am going to take this opportunity now to finally mention what sieving is (since it is in the title of my blog and all)! Sieving through soil is essentially separating the soil by particle size. In our slake test, we want to know how fast the soil sieves apart. We do this by placing it in water once its in its sieve basket. This will tell us a little bit about the stability of the soil aggregate (or ped), or its ability to resist breakdown by water. 

The sieve with the soil aggregate is placed in water for 5 minutes and examined for signs of dissolution. If the aggregate of soil makes it past 5 minutes without completely dissolving, it is then dunked 5 times. Throughout the test, a soil stability class is assigned. 


Assigning soil stability class: 

• If the soil is not even stable enough to sample, the soil stability class is 0 (which is really, really bad - the soil will not resist erosion to wind or water). 
• If 50% of the structural integrity is lost within 5 seconds of inserting the ped into water, the soil stability class is 1 (pretty bad). 
• If 50% of the structural integrity is lost within 5-30 seconds of insertion in water, the soil stability class is 2 (ok). 
• If 50% of the structural integrity is lost within 30 - 300 seconds after insertion or <10% of the soil remains on the sieve after 5 dipping cycles, the soil stability class is 3 (good). 
• If there is 10 - 25% of the soil remaining on the sieve after 5 dipping cycles, the class is 4 (pretty good).
• If there is 25 - 75% of the soil remaining on the sieve after 5 dipping cycles, the soil stability class is 5 (really good).
• If there is 75 - 100% of the soil remaining on the sieve after 5 dipping cycles, the soil stability class is 6 (REALLY GOOD i.e. make sure you don't have a rock instead of a soil aggregate!)

But we love doing it!

Finding peds is hard

The results were great! The average soil stability class was 4.43 with a standard deviation of 1.34! These results will be analyzed further to draw conclusions about the soil stability class of our different treatments. The results will also be analyzed in comparison with other data we gather on the trays to start making informed conclusions about whether green roofs with native plants and/or added native arbuscular mycorrhizal fungi perform as health natural habitats and improve heat insulation and storm water retention. More to come later!