Soil Health Testing – Why and How?
25 October 2023
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Simple, easy and effective methods are available to us to investigate the state of soil health. ‘Soil health’ the term for a soil’s ability to continue to provide multiple functions to sustain plant, animal, and human lives. It is estimated that 95% of world food is produced using soils. Using management in a way to encourage healthy soil is a target for reducing degradation (erosion and leaching), meeting our 2050 Net Zero targets in the UK, and ensuring global food security.
Soil health can be measured through biological, physical and chemical analyses. We will call the measures within each of the three groups ‘indicators’ because the indicate to us how well the soil is functioning. These include many in-field or lab-based methods – many of which are on the market, though not all are either useful or currently fit-for-purpose as routine indicators. For example, many of the biological indicators are incredibly useful in research but are currently not useful for routine analysis on-farm.
Understanding Aggregate Stability
Sometimes, these three categories are actually integrated and overlapping. The most interesting and valuable indicator might end up being aggregate stability. If we consider a healthy soil to be one full of roots, decaying organic matter, fungal networks, biological activity, pore space and the capacity to hold water – the aggregate stability test has scope to indicate if these are present in a soil.
Soil aggregates are large, medium, and small accumulated clumps of soil, essentially primary particles which are bound together to varying degrees and sizes. Aggregate stability is the measure of these aggregates to resist breaking apart via water, tillage or wind. A soil with strong aggregate stability will be resistant to these aggregates and will therefore lose less material. Poor aggregate stability will result in the easy loss of soil fractions.
Performing an Aggregate Stability Test
The aggregate stability test, sometimes called slake test, can be performed at home and by various methods. An easy example to do at home: use two clear containers nearly filled with water, use a mesh that will contain the aggregates when submerged but allow water access and flow to aggregates – and submerge soil aggregates. It can be useful to submerge once, remove, and submerge again to apply some force to the aggregates. In the photo below, comparing no-till (left), intensive (mid) and conventional tillage systems (right) soils, the effects of management on the ability of aggregates to resist water erosion are obvious. Finally, the aggregate stability test has been clearly identified as a rough estimate for organic matter content, furthering the idea that it is an invaluable indicator for the effect of management on soil health (Figure 2).
Doing Your Own Soil Health Checks
If you’re interested in doing your own soil health checks, the table below breaks down the different methods available to you as well as a quick explanation of what is necessary. You’ll note that a number of these can be done yourself with ease.
| Biological | In-practice? | Physical | In-practice? | Chemical | In-practice? |
|---|---|---|---|---|---|
| Earthworm counts | Easy! Grab a spade! | Soil structure - Visual Evaluation of Soil Structure (VESS) | Easy! Grab a spade! | Routine analysis - pH, macro and micro nutrients | Easy! Send samples to the lab! |
| Other macro-biology (nematodes, arthropods, beetles) | Not necessary as routine unless an observed issue, investigation of these as indicators still underway. | Aggregate stability | Easy! Bring some aggregates home and submerge in water. | Cation exchange capacity | Easy! Send samples to the lab! This is not routinely required, but will supply significant information on how to support management for your soil type |
| Microbial activity - CO2 respiration | Valuable in research, not currently valuable on-farm | Compaction – bulk density, penetration resistance | Easy! Use a bulk density ring – or any known volume – and calculate the density of soil before and after drying, also use a penetrometer to see compaction and depth of compaction | Organic matter content – loss on ignition or total carbon | Easy! Send samples to the lab! |
| Microbial abundance or species | It will tell us the volume or species present in soil, interesting but not necessary for routine use | Porosity – water holding capacity | Relatively easy at home, easier to send to a lab | ||
| Organic matter and parent material via soil colour | Colour provides some information as to whether OM is present at all, but is a vague estimate of quantity | ||||
References
Collier, SM, Green, SM, Inman, A, et al. Effect of farm management on topsoil organic carbon and aggregate stability in water: A case study from Southwest England, UK. Soil Use Manage. 2021; 37: 49–62. https://doi.org/10.1111/sum.12658
Hatfield, J.L., Wacha, K. and Dold, C. (2018), Why is SOIL ORGANIC MATTER so important?. Crops & Soils, 51: 4-55. https://doi.org/10.2134/cs2018.51.0205
Rose Boyko, SRUC
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