Soil Biology Testing: PLFA, Haney and 16S rRNA Sequencing

What Soil Biology Testing Actually Measures

Soil biology is a community, not a chemistry. A single gram of healthy agricultural topsoil hosts between 100 million and 1 billion bacteria, representing thousands of distinct species, alongside tens of metres of fungal hyphae, thousands of protozoa, and hundreds of nematodes at various trophic levels. Elaine Ingham's soil food web research programme, conducted at Oregon State University and USDA-ARS from 1984 through the 1990s and published across applied soil ecology journals of that period, established the functional architecture of this community: bacteria and fungi as primary decomposers, protozoa and nematodes as primary grazers whose feeding cycles release plant-available nitrogen, arthropods and earthworms as macro-fauna that physically restructure the habitat for all levels above them. The community converts organic matter into plant-available nutrients, constructs the aggregates that hold water and resist erosion, and symbiotically extends plant root systems through mycorrhizal networks that in healthy grassland soils can span several hundred metres of hyphal threading per gram. Every regenerative practice depends on this community functioning. Before 2015, an operator managing it was largely managing blind.

Three laboratory techniques now make different dimensions of this community visible at operator cost. Phospholipid fatty acid (PLFA) analysis identifies microbial functional groups from the membrane lipids extracted from a fresh soil sample, processed by gas chromatography-mass spectrometry. Different lipid biomarkers correspond to different organism classes: C16:1ω5c is the arbuscular mycorrhizal fungi (AMF) marker; branched and cyclopropyl fatty acids indicate gram-positive and gram-negative bacterial populations; ergosterol-adjacent markers separate saprotrophic fungi from the AMF fraction. Total PLFA gives microbial biomass in micrograms of carbon per gram of dry soil. The fungi-to-bacteria ratio derived from the full profile is the standard metric for whether a soil community is moving toward the fungal-dominated structure associated with high organic matter accumulation and the nutrient-cycling stability that characterises mature regenerative systems. The Haney test, developed by Rick Haney at USDA-ARS Temple (Haney et al., Soil and Tillage Research, 2008; Haney et al., Journal of Soil and Water Conservation, 2011), adds the activity dimension: a 24-hour CO2 respiration burst from a disturbed sample measures community responsiveness, while an H3A extractant formulated to mimic root exudates reveals which nutrient fractions are biologically accessible rather than merely chemically bound in the soil matrix. 16S rRNA and ITS amplicon sequencing reaches the deepest resolution: extract total soil DNA, amplify the V3-V4 region of the bacterial ribosomal RNA gene (16S) or the fungal internal transcribed spacer region (ITS1 or ITS2), sequence on an Illumina instrument, and classify against reference databases using QIIME2 or DADA2 pipelines against SILVA (bacteria) and UNITE (fungi). The result is a community profile at genus level across hundreds to thousands of distinct taxa per sample, with presence/absence data for known pathogens and verified beneficial genera.

These are laboratory tests, not field sensors. Each requires a physical soil sample collected at a point in time, posted or couriered to a laboratory, processed over seven to twenty-one days, and returned as a structured report. They do not provide continuous monitoring of soil conditions. The continuous temporal layer is what the in-situ sensor network provides: volumetric moisture, temperature, and electrical conductivity at fifteen-minute to hourly resolution, logged to the cloud and queryable in real time. The two instrument types address fundamentally different questions from the same soil. The laboratory test establishes which biological community is present and whether it is changing on a seasonal or annual timescale. The field sensor tells the operator whether the conditions between test dates are supporting or stressing the community the laboratory measured. Quarterly PLFA without a moisture sensor misses the August drought that suppressed the fungal community the spring PLFA reported. A moisture sensor without quarterly PLFA reports conditions but not whether the community equipped to respond to those conditions actually exists.

The Cost-Collapse Arithmetic: 2010 to 2025

The cost collapse has three structural drivers. First, commercial laboratory standardisation: Ward Laboratories (Kearney, Nebraska) moved PLFA from a specialist ecological commission to a standard agricultural analysis item, reducing the per-sample price from 200 to 500 USD for a small ecological survey run to 50 USD for a routine farm sample (Ward Laboratories, 2024-2025 pricing schedule). Second, the maturation of the Haney test from USDA-ARS research protocol into commercial product: between 2012 and 2016, a network of commercial soil laboratories adopted the method, and competition between providers drove the price to 35 to 50 USD per sample, where Ward Laboratories, Texas A&M AgriLife Extension, and equivalent providers now operate. Third, and most structurally significant: the Illumina sequencing instrument cost curve. The Illumina HiSeq 2000, launched in 2010, required approximately 600,000 USD per instrument and dedicated bioinformatics infrastructure. By 2024, the Illumina iSeq 100 lists at approximately 19,900 USD per unit (Illumina 2024 product pricing), and per-sample sequencing costs have fallen more than 99 percent since 2008 according to the National Human Genome Research Institute's sequencing cost tracking programme (NHGRI, data series updated 2023). Agricultural soil metagenomics runs on the same instrument cost curve that collapsed clinical genomics from a multi-million-dollar research project to a routine diagnostic.

The practical arithmetic for a single regenerative field in 2025: a quarterly PLFA protocol across one year costs 200 USD at Ward Laboratories prices (four samples at 50 USD). Adding one Haney panel annually brings the total to 245 USD. Adding one 16S rRNA and ITS sequencing run through Biome Makers or an equivalent independent provider brings the annual total to 395 to 545 USD per field. An operator who needed equivalent biological intelligence in 2012 would have spent 2,000 to 5,000 USD on a combination of specialist ecological consultancy, academic laboratory access, and paid interpretation. The cost-collapse is not incremental. It is the difference between a specialist research budget and a farm input line item smaller than one tonne of bagged nitrogen fertiliser.

PLFA, Haney, Sequencing: Three Tests, Three Decisions

PLFA is the entry point and the quarterly tracking instrument. The profile returns total microbial biomass, active fungal biomass, the fungi-to-bacteria ratio, and the AMF biomarker C16:1ω5c, which quantifies arbuscular mycorrhizal fungi separately from total fungal biomass. A regenerative operator transitioning a field from tillage-based management to no-till and diverse cover crops typically sees a depressed fungi-to-bacteria ratio in year one: the community is bacteria-dominated because tillage historically favoured fast-cycling bacterial decomposition and disrupted fungal hyphae. Quarterly PLFA tracks whether the ratio shifts over the following two to four years as cover-crop root exudates and undisturbed aggregate structure establish the hyphal food source. Ward Laboratories processes PLFA by GC-MS, reports the results as a profile of approximately 30 fatty acid biomarkers with a normalised fungi-to-bacteria ratio and AMF biomass value, and delivers the PDF to the operator within seven to ten business days (Ward Laboratories, 2025 service guide). No interpretation platform subscription is required. The report is the operator's to read, annotate, and share with any independent agronomist they choose.

The Haney test adds the biological activity dimension that PLFA does not measure directly. The 24-hour CO2 burst from a disturbed soil sample reflects active microbial metabolism: a high burst value in a transitioning field indicates the community is responsive and decomposition pathways are functioning; a low value in a field that tests as biologically diverse by PLFA indicates the community is present but stressed or dormant. The H3A extractant releases nitrogen, phosphorus, and potassium from organic matter fractions in a way that approximates biological availability from plant-root-exudate pathways rather than total chemical content. Conventional Mehlich-3 or Bray-1 soil fertility tests extract with strong acid and dissolve mineral-bound nutrients that a plant may never access biologically; the H3A panel isolates what is genuinely accessible through the microbial mineralisation route. Rick Haney, the USDA-ARS agronomist who developed the test at the Temple, Texas research programme across the period 2004 to 2011, designed it as a biologically-grounded replacement for the input-intensity recommendations that conventional nutrient management produces. The 45-USD Ward Laboratories panel returns CO2 burst respiration, water-extractable organic C and N, H3A-extractable N, P, and K, and a calculated Soil Health Score that combines the respiration and organic-carbon fractions into a single index.

16S rRNA and ITS sequencing is the diagnostic instrument rather than the routine monitoring instrument. The cost (100 to 300 USD per sample at 2024 commercial rates) and the turnaround (ten to twenty-one days at most commercial providers) make it impractical as a quarterly farm tool. Its value is in characterising the baseline community before a major management change, verifying that the community two to three years into transition has actually shifted toward the target structure, and diagnosing specific problems: the presence of known soil-borne pathogens (species-level confirmation of Fusarium oxysporum, Pythium ultimum, or Phytophthora genera), the absence of expected beneficial AMF genera (Glomus, Rhizophagus irregularis), or the dominance of indicator taxa associated with compaction and anaerobic conditions. Biome Makers' BeCrop test (150 to 300 USD per sample, 2024) delivers a proprietary interpretation layer on top of the standard 16S and ITS sequencing workflow, including a biological index score, community diversity metrics, and ranked agronomic recommendations generated from the company's reference database. Pattern Ag (an AGCO subsidiary following the 2022 acquisition, AGCO press release August 2022) focuses specifically on soil-borne pathogen detection and crop-health risk scoring rather than full community profiling, at approximately 175 to 250 USD per test in 2024.

Vendor Landscape and the Data Sovereignty Choice

Ward Laboratories (Kearney, Nebraska) is the most accessible independent option for North American operators. PLFA at 50 USD per sample, Haney panel at 45 USD, conventional fertility testing available separately on the same order. Results are delivered as a PDF. There is no platform subscription, no data-sharing agreement beyond the sample submission terms on the order form, and no parent company with an agronomic product portfolio into which the results route. The operator owns the report. Regen Ag Lab (South Australia), founded by Dr Christine Jones, specialises in PLFA with particular emphasis on glomalin-related soil protein (GRSP) quantification for mycorrhizal carbon-capture verification, at 55 to 75 USD per sample in 2024. Australian and New Zealand operators typically route to Regen Ag Lab; European operators can use Ward Labs via international posting or regional equivalents including A&L Biologicals (Canada) and Eurofins Agro (Netherlands and UK) for equivalent biological panels at broadly comparable prices. Texas A&M AgriLife Extension offers the Haney test through the university extension service at prices competitive with Ward Laboratories, with the institutional authority of the original developer's programme behind the methodology.

The sequencing vendor choice carries a data sovereignty dimension the simpler lab tests do not. Trace Genomics, which operated as an independent soil microbiome sequencing platform from 2016, was acquired by Koch Agronomic Services in June 2022 (Koch Industries press release, June 2022). Koch Agronomic Services is the Koch Industries subsidiary that operates Agrotain nitrogen stabiliser, Guardian 0-0-1 sulfur fertiliser, and a portfolio of crop-nutrition products sold into the same farm operations that now generate microbiome data through Trace Genomics. The structural logic is the same one the Data Sovereignty spoke identifies at the field-telemetry layer: an operator pays to generate biological intelligence through a platform that routes the resulting dataset toward a parent company whose product revenues are directly informed by agronomic recommendations that data supports. The operator pays for the sample, the sequencing, and the analysis. The intelligence then flows toward a fertiliser portfolio. Biome Makers (Valladolid, Spain, established 2015) remains an independent company as of 2025, does not route to an agrochemical parent, and provides a farmer-controlled BeCrop portal with exportable reports. Pattern Ag is an AGCO subsidiary, but AGCO's commercial interest centres on precision planting and harvesting equipment rather than nutrient products, which makes the data-capture incentive structurally different. For operators who require the highest data sovereignty assurance across all three test types, Ward Laboratories for PLFA and Haney combined with Biome Makers for sequencing is the appropriate combination.

Integration: Lab Tests and the Regenerative Decision Cycle

Laboratory soil biology testing and in-situ field sensors serve fundamentally different temporal and analytical roles in a regenerative operation. The in-situ sensor network delivers continuous volumetric moisture, temperature, and electrical conductivity at fifteen-minute to hourly resolution. The laboratory test delivers a biological community snapshot at seven-to-twenty-one-day turnaround. An operator who has only the sensors knows whether soil moisture is at field capacity but not whether the mycorrhizal fungi that would activate at that moisture level are present in sufficient biomass. An operator who has only the laboratory results knows the community profile from the last sampling date but cannot see whether a dry August has collapsed activity in the intervening months. The two tools answer complementary questions. Neither substitutes for the other, and the combination is what makes soil biology management as a practice rather than a hope.

The practical decision cycle for a field transitioning to regenerative management: run baseline PLFA and Haney before the first cover-crop establishment season, and repeat after the first full growing season to establish the direction of travel. Continue quarterly PLFA for the first two years to track the fungi-to-bacteria ratio trajectory season by season. Add 16S and ITS sequencing in year one and year three to verify community composition at genus level: confirming AMF genera establishment, checking for pathogen presence before any management decisions are made on the basis of community counts alone. Once the trajectory is established and two consecutive annual sequencing runs confirm the target community structure, move to annual PLFA monitoring and biennial sequencing as a maintenance protocol. The total annual cost for this programme at Ward Laboratories and Biome Makers price points runs 395 to 545 USD per field: four PLFA at 50 USD (200 USD), one Haney panel at 45 USD, and one sequencing run at 150 to 300 USD. That is less than the application cost of a single fungicide treatment on a field the same size, and it is generating baseline data that a carbon verification programme, a soil health grant application, or an independent agronomic review can use directly.

The operator who runs this protocol across three years has built something that did not exist before the cost collapse: a documented biological baseline for their fields, a quantified community transition trajectory, and evidence of biological change that is independent of yield data, portable across advisors, and legible to any programme that requires measurement-based proof of soil health outcomes. The instruments that make this possible now cost less than one tonne of bagged fertiliser per field per year. You cannot manage what you cannot see. At 50 US dollars a sample and a PDF delivered in ten days, you can see it.