The Fritz study on the soil microbiome: what it reports – and what it does not

A study published in 2024 by the research group around Jürgen Fritz (University of Kassel) is often cited in biodynamic circles as proof that "the preparations work". That makes a sober look worthwhile — not to celebrate the study or tear it apart, but to separate what the study text actually says from what is read into it beyond that.

What it was about

The study (Milke, Rodas-Gaitan, Fritz et al., ISME Communications, 2024) compared the soil microbiome under biodynamic and under purely organic management. It examined 254 soil samples from 3 sites in Germany and 21 in France. Using gene sequencing (16S for bacteria, ITS for fungi) and a database comparison, it determined which microorganisms occur and which of them are classified by calculation as putatively growth-promoting.

What the study reports

The reported finding: in the biodynamically managed samples there were more gene variants of microorganisms considered putatively plant-growth-promoting than in the samples that were only organically managed. Against this background, the authors interpret the preparations as a kind of microbial "inoculation" of the soil. That is the content of the paper.

What does not follow from it

Here precision matters more than enthusiasm — in both directions.

First, the study compares biodynamic with organic, that is, two farming methods that are already similar. A difference found there says nothing about the gap to conventional agriculture and nothing about the anthroposophical justifications for the method.

Second, "growth-promoting" here is a prediction from the database comparison, not an effect measured in the field. The study shows a shift in the composition of microorganisms — not that this leads to more or better harvests.

Third, and this is the decisive leap: even if an altered microbiome can be detected in the immediate surroundings of tiny amounts of fermented herbs, it does not follow that the whole field therefore becomes more fertile. From a local finding to an effect over the whole area is a long way, and not one that has been demonstrated.

In line with this, the researchers themselves stress that the effects are not stable over the years — sometimes something shows up, the following year hardly anything.

Putting it in context

The biodynamic method is at its core a belief system; by far the greatest part of its assumptions cannot be tested by natural science. The Fritz study is one of the few points at which anything can be measured at all — and it measures exactly one narrow slice: a shift in the microbiome when comparing soils. That is interesting and seriously collected. But it is no proof that "the preparations work" in the broad sense, and certainly no confirmation of the anthroposophical idea of how they work. Anyone who sells the study as "now it is proven" overstretches it — anyone who ignores it suppresses a real finding. How this fits into the overall picture of what can and cannot be demonstrated is set out under Biodynamics and science.

Frequently asked questions

What did the Fritz study report?

That biodynamically managed soils contained more putatively growth-promoting microorganisms than soils that were only organically managed — a shift in the soil microbiome when comparing the two farming methods.

Does the study prove that the preparations increase yield or make the field more fertile?

No. It shows a shift in the microbiome; the growth-promoting function is predicted by calculation, not measured in yield. Concluding from a local microbiome effect that soil fertility increases across the whole area is not supported. The effects also vary from year to year.

Where can I find the study?

Milke, Rodas-Gaitan, Fritz et al., "Enrichment of putative plant growth promoting microorganisms in biodynamic compared with organic agriculture soils", ISME Communications 4(1), ycae021 (2024), open access.