How to read a soil DNA report without a biology degree

More soil products are starting to show lab data, which is good — but a sequencing report is not an obvious document if you haven’t seen one before. Here’s how to read one, using our own as the worked example.

Species count

What it says: how many distinct organisms were identified in the sample. Ours: 1,589.

What it means: a raw count of diversity. More is generally better, because a diverse community is harder to knock over. But don’t stop at the headline number — the distribution matters more.

What to look for: how concentrated the population is. In ours, the top 10 species are 29% and the top 100 are 67%, leaving a long tail of nearly 1,500 organisms. If a report shows a big count but the top few species dominate 80% of the population, that’s a narrow community wearing a big number.

Bacteria-to-fungi ratio (B:F)

What it says: the balance between the two main groups. Ours: 69:1, strongly bacterial.

What it means: different plants want different balances. Annuals — vegetables, most flowers, lawns — evolved in bacterially dominated soils and want fast nutrient cycling. Perennials, shrubs and trees lean fungal. Forest soil might run 1:1 or fungal-dominant.

What to look for: a match to what you grow. Strongly bacterial is right for a vegetable bed and not what you’d choose for a woodland border. A high B:F is not a defect and a low one is not a virtue — it’s a fit question.

Pathogen screening

What it says: whether known disease organisms turned up among the most abundant species. Ours: zero in the top 100.

What it means: the material was processed to temperature and handled properly.

What to look for: the scope of the claim. Ours is specific — the hundred most abundant species. Precision here is a good sign. Be more careful with vague absolute claims, which are harder to support.

Functional potential

The part people find most confusing, and the most useful once it clicks.

What it says: not what the organisms are, but what they’re equipped to do — scored as a percentage. Ours includes iron acquisition 85%, nitrogen fixation 69%, phosphorus mobilisation 64%.

What it means: the lab looks at which functional genes are present across the community. An 85% iron acquisition score means the community is very well equipped to convert iron into forms roots can take up.

Important: these are potentials, not guarantees of yield. Biology is equipment, and equipment still needs conditions — moisture, temperature, organic matter — to do its work. A soil report tells you what showed up for the job, not what the harvest will be.

What to look for: functions matched to your actual problem. Sandy soil that won’t hold anything? Carbon fixation and organic matter building. Yellowing leaves? Iron acquisition. Poor fruit set? Phosphorus and potassium.

Mycorrhizal fungi

What it says: whether root-partnering fungi are present, usually split into arbuscular (AMF) and ectomycorrhizal (ECM).

What it means: AMF partner with most vegetables, flowers and grasses, extending a root’s reach for water and phosphorus. ECM partner mainly with trees.

What to look for: AMF presence if you’re growing a vegetable garden. Ours has both, at an ECM:AMF ratio of 1.92:1.

The question worth asking

The most useful thing about any lab report isn’t a single number — it’s that the number exists, has a lab’s name attached, and can be checked.

When a bag says “rich in beneficial microorganisms,” ask which ones, how many, and who measured it. If there’s no answer, that phrase is a decoration. If there is an answer, you can evaluate it — and now you know how.