Lance Gunderson explains the science behind the Haney and PLFA soil health tests, and how to interpret test results.

Soil is a complex ecosystem that provides habitat for all kinds of micro-organisms. These include bacteria, fungi, protozoa, nematodes, earthworms and more. These organisms control much of the nutrient cycling in your soil. They breakdown crop residues, store plant nutrients, create stable organic matter in the form of humic acid, and help build soil structure, thus reducing compaction and erosion, while increasing water holding capacity and allowing for deeper root structures.
The relationship between different microorganisms and plants is dynamic. Predatory protozoa eat bacteria which releases nitrogen into the soil. Symbiotic bacteria and fungi aid the plant in acquiring more nutrients.
Phospholipid fatty acids (PLFA) are found in the cell membranes of living organisms, and are used to estimate the living microbial biomass in your soil. Different kinds of cells have unique biomarkers, or signature fatty acids, which helps identify the presence or absence of various microbial groups of interest.
PLFA test results are a snapshot of your microbial community structure and abundance at the time of sampling. As environmental conditions such as pH, temperature, and moisture change, so does your microbial community. These communities are also influenced by soil type, organic matter, intensity and type of tillage, crop rotations, cover crops, and herbicide or pesticide applications. You can use the ability of microbial communities to change rapidly as a tool to compare different management decisions, to see how your decisions affect soil health and fertility.
Since there is no baseline “normal range” for biological testing like there is for chemical analysis, this test is most useful for making comparisons between management conditions: till vs. no-till, different fertilizer applications, crop rotations, grazing vs. no grazing, etc.

The PLFA test provides values for: Total Living Microbial Biomass; Total Bacteria; Gram (+) and (–) Bacteria; Actinomycetes; Rhizobia; Total Fungi; Arbuscular Mycorrhizae; Saprophytes; Protozoa; Fungal: Bacterial ratio; Predator: Prey ratio; Gram (+): Gram (–) ratio; Stress and Community Activity ratios.