Biological indicators can be the key to healthy soils in Europe

Healthy soils are crucial for producing food, storing carbon, purifying water, and preserving biodiversity. But today, more than half of the EU’s soils are in poor condition – and the problems risk being worsened by climate change. That is why the EU has set an ambitious target: all soils should be healthy by 2050.

– To get there, we need better tools to measure and monitor soil health. So far, the focus has been on chemical and physical properties such as nutrient levels and structure, but now we are increasingly looking at the soil’s biological life – the teeming community of microorganisms, earthworms, and small invertebrates that make the soil alive, explains Maria Viketoft.

Bioindicators show potential – but more data and coordination are needed

These bioindicators can provide important information about the soil’s ability to deliver ecosystem services such as fertility, carbon storage, and resistance to erosion.

A new study within the EU project  EJP SOIL MINOTAUR explored the possibilities of developing assessment criteria for such biological indicators. The results show that there is still not enough data to establish common reference values at EU level, and differences in sampling methods and soil classification between countries make comparisons difficult.

– We can see that bioindicators have great potential, but that we need more coordination and more long-term measurements in order to make full use them, says Maria.

In some countries, such as France, researchers have already made more progress. There, they have managed to establish reference values for, for example, earthworms in different soil types, thanks to extensive national surveys.

Tiny worms with big importance for agriculture

The study examined nematodes, tiny worms that play an important role in soil nutrient cycles. Maria Viketoft used data from long-term field experiments and farms in the Netherlands and Sweden to analyze nematode abundance, diversity, proportion of plant-parasitic species, as well as various indices based on the composition of nematode communities that reflect ecosystem status and complexity.

– We found that nematodes can function as indicators of soil health, but differences in sampling and analysis methods between countries make it difficult to compare data directly. Some indicators, such as the indices that reflect nutrient availability and ecosystem complexity, are more robust because they are not affected by how samples are processed. However, we need more data from different soil types and farming systems in order to establish clear reference values for how nematodes can be used as bioindicators on a larger scale, Maria explains.

Bioindicators could become a natural tool for healthier soils

With the new EU soil monitoring directive, more member states are expected to develop similar systems.

– In the long run, we hope that standardized methods and better data will make it possible to compare soil health between countries – and that bioindicators will become a natural tool in the work for healthier soils, concludes Maria.

Read more

Read the full study Establishing assessment criteria for soil bioindicators: insights from case studies in Europe in the scientific journal Ecological Indicators.