Soil Biology Assessment Calculator

The calculator's food-web classification is based on the fungal-to-bacterial PLFA ratio: below 0.1 it labels the soil bacterial-dominated (typical of tilled cropland), 0.1-0.2 moderately bacterial, 0.2-0.5 balanced, and 0.5 and above fungal-dominated like a mature forest floor. Fungal networks take longer to establish and are more easily disrupted by tillage, so a higher ratio generally signals a soil food web that's had more time undisturbed to develop fungal biomass alongside bacteria.

The composite score is built from four separately capped subscores rather than a simple average: total biomass contributes up to 30 points, the fungi:bacteria ratio up to 25, AMF share up to 20, and the gram+:gram- stress band up to 25, with the stress subscore awarding full points only when that ratio sits in the normal 0.5-2.0 range. Weighting them this way means a soil can't compensate for a stressed, imbalanced microbial community purely by having high total biomass.

The calculator treats a gram+:gram- ratio below 0.5 as unusual and flags it to verify your lab results, since typical agricultural soils fall in the 0.5-2.0 range and values above roughly 2.0-3.0 (not below) are the classic signal of drought or compaction stress. A very low ratio isn't assigned a specific stress interpretation here — it's flagged as an outlier worth double-checking against the original lab report rather than a diagnosed condition.

No — this tool interprets numbers from an existing PLFA lab analysis; it doesn't estimate or measure microbial biomass on its own. You need a soil sample already analyzed by a lab reporting total, fungal, bacterial, AMF, and gram-positive/gram-negative PLFA values in nmol/g before the ratios, biomass carbon estimate, and composite score here mean anything.