Soil stability (soil slaking test)

Main authors:	Abdallah Alaoui and Gudrun Schwilch
Editor:	Jane Brandt
Source document:	Alaoui, A. and Schwilch, G. (2016) Soil quality and agricultural management practices inventory at case study sites. iSQAPER Report 28 pp

Importance

Slaking is the breakdown of large, air-dry soil aggregates (>2-5 mm) into smaller sized microaggregates (<0.25 mm) when they are suddenly immersed in water. Slaking indicates the stability of soil aggregates and resistance to erosion, and suggests how well soil can maintain its structure to provide water and air for plants and soil biota when it is rapidly wetted. High soil stability suggests that organic matter is present in the soil to help bind soil particles and microaggregates into larger, stable aggregates. Slaking results in detached soil particles, reduced infiltration and plant available water, and increased runoff and erosion and causes surface sealing.

Assessment

Select 3 air-dry aggregates, 4–6 cm diameter. Place soil fragments in the mesh of 1 cm diameter. Observe the soil fragment for 5–10 minutes. Refer to the stability class table below to determine the scores.

VSA fig07.2
Good VSA fig07.1
Moderate VSA fig07.0
Poor

Soils with high SOM do not readily slake (fall apart) when wetted (left side). The soil on the right would be more likely to crust after a heavy rain.