Tech Tuesday: Biological Indicators

The PES Technologies unit is a handheld, in-field soil health indicator device, providing crucial time saving and comprehensive data to make soil management decisions. A vital but underutilised aspect of soil health is biological indicators. Biological indicators are the living components of your soil and are often the first indicators of soil health change, this sheet will give you an understanding of how to interpret your biological results.

Context is Key: The Scale
Results appear on a scale, but high/low does not mean good/bad. Your soil’s texture, such as sandy vs. clay, dictates its natural capacity. As a rule, heavier clay soils will be able to hold onto organic matter and microbial life more easily. To separate inherent soil traits from management impacts, always compare your field results to an uncultivated reference sample (e.g., under a hedgerow) within the same soil texture.

The Biological Trio
Microbial Biomass : This is the total “weight” of living microbes. Higher levels generally mean better nutrient availability, disease suppression, and soil structure. However, biomass is limited by your soil’s pH and organic matter; a high organic matter index with low biomass is a red flag that warrants investigation. The PES ScentsCheck app will not tell you the type of microbial life found in your soil, e.g. bacteria, fungi etc. Get in contact with your agronomist to discuss your results for further clarification.

Microbial Respiration: This measures how active your microbes are as they break down organic matter and release CO₂. While activity is usually positive, high respiration without a corresponding high biomass suggests the community is “wasting” energy due to stress, such as drought or excessive disturbance.

Metabolic Quotient: The ultimate efficiency metric. Calculated by dividing respiration by biomass, a lower value indicates a highly efficient system where less carbon is lost to the atmosphere. Because respiration can react within hours to change, this quotient is your fastest indicator of whether your management practices are supporting or stressing your soil’s biology.