When looking at a BIOTREX Report, readers often notice that there are no units next to the results. This question comes up often, and the answer reveals something fundamental about how soil life is measured and understood.
Measuring vs. Describing
In most laboratory tests, results come with physical units because they describe measurable quantities – kilograms of weight, degrees of temperature, milligrams per litre of nutrients. These are direct measurements of something physical.
BIOTREX, however, doesn’t measure “how much” of something exists. Instead, it evaluates how the microbial community behaves – how active, diverse, and functionally capable it is. To do this, we record colour changes that occur as soil microorganisms use different carbon sources in dozens of small test wells on a Biolog EcoPlate™(31 test wells) or DGC Plate (95 test wells).
Each colour change is measured using optical instruments and technically has a unit, such as optical density (OD) or Omnilog Units (OU). But these are just the raw signals. What matters is how those signals combine to describe the soil’s living system as a whole. Once thousands of such readings are processed and standardised, the units lose their meaning. What remains is a dimensionless indicator – a number that expresses relationships and patterns rather than physical amounts.
Why Microbial Activity Has No Standard Unit
Unlike temperature or mass, there is no universal unit for microbial activity. Soil microorganisms perform many simultaneous processes – decomposition, nutrient cycling, disease suppression, carbon storage – and no single measurement can represent all of that. Even in related fields, “enzyme activity” is expressed in inconsistent units that vary from lab to lab.
BIOTREX indicators overcome this by focusing on comparability rather than absolute quantities. Each indicator is normalised against a European reference database, where values are scaled so that the average is 50 and the standard deviation is 20. This means a score of 70 reflects noticeably higher microbial performance, while 30 indicates lower-than-average activity.
One exception is the Microbial Performance Indicator, which retains a special historical “BIOTREX unit.” Created in Japan, it was originally calibrated so that a value of one million represented “good” soil. Today, this scale remains for consistency across BIOTREX’s global database, ensuring long-term comparability between regions and research projects.
BIOTREX indicators are not an exception in ecological research. Many established ecological indices, such as the Shannon biodiversity index, also have no units. The Shannon index doesn’t measure physical mass – it reflects how evenly different species share their environment, capturing the structure of a community rather than its size. BIOTREX indicators follow the same logic: they summarise microbial diversity and functional performance on a unit-free, standardised scale that allows clear, comparable interpretation across soils and regions.
more than numbers
Dimensionless doesn’t mean meaningless.
On the contrary, it makes BIOTREX results universally interpretable. A farmer in Spain and a researcher in Poland can both understand what a score of 60 or 80 means, without worrying about local calibration or different lab instruments.
And for those who prefer classical scientific metrics, BIOTREX can also provide standard indices such as the Shannon or Margalef diversity index, calculated from the same dataset.
In short, BIOTREX indicators don’t have units because they measure something far more complex than a physical quantity – they measure how well your soil lives and works.
