Testing soil for legume fatigue (DiverIMPACTS, ReMIX, LIVESEED Practice Abstract)

Summary

Benefits
The test offers reference points regarding the soil contamination with the pathogens mentioned above and can, thus, reveal the need for a cultivation break. Refraining from cultivating on contaminated soils helps to avoid high yield losses due to legume fatigue.
Practical recommendation
1. Extract 10 litres of humid soil from the field plot you wish to examine and sieve it down to a grain size of 10 mm.
2. Moisten dry samples and mix them evenly.
3. Fill four aluminium trays with the humid soil and store the re-maining soil.
4. Cover the trays filled with soil with tinfoil and place them in the baking oven. Sterilise the samples for at least 12 hours at 70-100°C in the oven.
5. Let the aluminium trays cool for 12 hours after sterilisation.
6. Mark four flowerpots with "R" (for untreated reference) and an-other four with "H" (for heat-treated soil).
7. Fill the four H-flowerpots with the heat-treated soil and fill the four R-flowerpots with the untreated soil.
8. Place 5-10 legume seeds (depending on seed size) in each pot and cover them with 0.5 cm of the same type of soil.
9. Place the H and R pots randomly in a tray with some water and keep them in a sheltered place with at least 18°C and daylight.
10. Keep the pots humid during about 6 weeks by pouring water into the trays.
Practical testing
- After about 6 weeks, the test can be evaluated. If the reference plants have germination problems and/or are growing poorly and turning yellow due to heavy infestation, the evaluation can take place earlier.
- For evaluation, cut all plant shoots at the stem 2 cm above the soil, and weigh the shoots of each pot separately. Make a note of the shoots' weight.
- Dividing the weight of the untreated reference plants by the weight of the plants from the heat-treated soil gives a ratio which can be used as an indicator for legume fatigue.
- For example, if the weight of the plants in the untreated soil is 180 g and the weight of the plants with the heat-treated soil is 200 g, then; 180 g/200 g = a ratio of 0.9.