Course Content
Introduction
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Introduction
Soil fertility
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Soil fertility
Chemical soil fertility
Biological soil fertility
Physical soil fertility
One Health Approach
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One Health approach
Soil sampling methods
Spade diagnosis to assess soil structure at field scale
Earthworm sampling
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Three ecological categories
Advantages and disadvantages of the techniques
Instructions: Spade test followed by earthworm extraction
Conclusion
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Conclusion
Takeaways about Environmental initiatives (soil and food production)
References
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References
Annex
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Weed types
Soil types
Environmental initiatives (soil and food production)
About Lesson

The extraction of earthworms can be combined with a spade test, which is based on the approach of Capowiez (2012). Note potential negative side‐effects of the combination on sampling efficiency. After the excavation of soil for the spade test from the 30 × 30 x 30 cm volume, the earthworm burrows and macro pores are identifiable at the bottom of the hole. They indicate the activity and density of deep burrowing soil organisms. The spade sample can be described according to Section 3.3.1 and afterwards it is hand sorted for earthworms as described above. Then the irritating solution is poured into the hole following the instructions above to collect the earthworms.

Material

  • Instruction and determination/identification help (ecological categories)
  • Measuring tape / yardstick
  • Spade
  • Plastic sheet
  • Plastic gloves
  • Glass jars
  • Waterproof pen for marking the jars
  • Paper, pen
  • Camera
  • Stopwatch
  • Watering can
  • Canister whit 9 litres of water (for three extractions)
  • 2 small commercial mustard pots (150 g *2) (for 9 litres of water)
  • Laboratory balance
  • 4% Formalin solution
  • Filter paper

Prepare mustard solution

  • for each watering, dilute 2 small commercial mustard pots (150 g *2) in a watering can with 10 liters of water.
  • For each hole sampled: applied in total around 10‐20 liters of spraying diluted mustard.

Hand sorting

  • Excavate the volume of 30 × 30 x 30 cm and put the soil on the plastic sheet. Examine the crumbs for remaining earthworms.
  • Look at the roots in particular, since they often hide in the dense roots below the shoot.
  • Combine the earthworms with the previous ones.

Counting earthworm burrows

  • Clear and level the surface at the bottom of the hole with a sharp knife to make the earthworm burrows visible. Count the open macro‐pores on the total 30 × 30 cm area – use a frame to limit the sampling area.

Measure infiltration

  • Place a yardstick at a visible area of the whole.
  • Pour 3 litres of mustard solution into the whole.
  • Start a stopwatch immediately and stop record the time needed for infiltration per cm.

Spread irritant solution in the hole

  • Every 10 minutes apply one third of the irritant test solution in the test area.
  • The last worms can come out of the ground up to 30 minutes after the last dose ‐ so wait.

Pick up the earthworms

  • Carefully pick up worms with a tweezer as soon as they have completely come out.
  • Place the individuals in a labelled tray, filled with moist paper.
  • Rinse them with water to remove the irritant.

In the laboratory

  • Wash and count immediately.
  • Place individuals on filter paper to dry them superficially.
  • Differentiate between adult (with clitellum / ring) and juvenile (without clitellum) depending on the research question.
  • Group them into ecological categories by consulting an expert or a classification guide.
  • Experts can help with the identification of the species.
  • Count individuals (density) and weigh them with a good balance (biomass).
  • Calculate the density and biomass per square meter.

Earthworm conservation and transport

Earthworms can be conserved in:

  • 4% formalin: DNA will be damaged (solution for earthworm transport by air).
  • 70% ethanol: DNA will be preserved (however, the ethanol has to be changed in the first weeks and photos help to identify the colour that changes in ethanol).
  • Transport in a solution of 4% formalin is possible.
  • Classification of results

The following factors contribute to a high earthworm density:

  • Little disturbances in soil (soil tillage, plant protection)
  • Vegetation (grassland, green manure)
  • Dead plant material (compost, mulch)

Information on density and biomass differs widely in the literature. Main reasons for the different presence are the specific conditions at each location. In addition, there is small‐scale inhomogeneity in the soil, as well as seasonal differences in the distribution of earthworms. The population densities in soil depends on the intensity of farm practices (soil tillage, input of pesticides, diversity of crop rotation, use of heavy machinery), food supply (below and above ground) and soil moisture (rainfall, irrigation, …).

Regarding total density and biomass, in some countries, there are national or regional thresholds that can indicate if the amounts of earthworms found are at low, medium or high level. For instance in France, the threshold is at 150 earthworms per hectare (Cluzeau, 2015). However, this threshold does not take into account soil and climate conditions. 

It is recommended to take repeated measurements over time (years) to monitor the change and confirm differences.

Note: The earthworm biomass better represents the ecological effect.

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