Which decision will the test help with?
Are you tracking a management change, planning fertilizer, or ordering tests for a conservation program? Those uses require different evidence. The Haney test can add useful information about biological activity and nutrient cycling, particularly when the same field is sampled consistently over several years. A nutrient credit or a single score needs a separate check before it changes a fertilizer rate [34] [41].
Developed through USDA Agricultural Research Service work in Temple, Texas, the original Soil Health Tool combines a 24-hour CO2 burst, water-extractable organic carbon (WEOC) and nitrogen (WEON), and nutrients extracted with H3A [1]. H3A uses dilute organic acids and has changed since its first publication in 2006; the 2017 H3A-4 formulation removed lithium citrate [2] [3] [4]. The report then uses measured values to calculate a Soil Health Score and estimated nutrient availability. Laboratory packages have also evolved: Ward’s current Soil Health Assessment lists conventional nutrient extracts alongside biological measurements, while Regen Ag Lab’s Haney package lists H3A [51] [52]. Confirm the package contents before comparing reports.
How to read the report
The published 2018 method dries soil at 50 °C, sieves it to 2 mm, and uses separate water and H3A extracts plus a dried-and-rewetted sample for respiration [1]. Incubation and detection methods can differ: Ward’s archived instructions specify infrared CO2 analysis at 24 °C, while MVTL’s information sheet specifies 25 °C [5] [6]. WEON is calculated as total water-extractable N minus nitrate-N and ammonium-N. It is an estimate of an extractable organic pool, not a direct measurement of the N a crop will receive.
The lines on a Haney report and what each one is
| Report line | How it is produced | What it can tell you | Interpretation boundary |
|---|---|---|---|
| 1-day CO2-C, usually mg C/kg soil (ppm) | CO2-C released during a 24-hour incubation of dried, rewetted soil [1] [5] | Potential microbial activity under the test conditions | A respiration indicator, not a direct microbial count or field CO2 flux. Compare the same incubation and rewetting method. |
| WEOC, ppm | Organic carbon in the water extract [1] | A water-extractable carbon fraction relevant to microbial activity | It is not total soil organic carbon. Ward reports that many samples fall around 100-300 ppm; this is a laboratory observation, not a universal target [7]. |
| WEON, ppm | Total water-extractable N minus nitrate-N and ammonium-N [5] | An organic N fraction used in the nutrient-credit calculation | The pool size does not establish how much N will mineralize during the growing season. |
| Water-extract organic C:N | WEOC divided by WEON [7] | The balance of C and N in this extract | It differs from whole-soil or residue C:N. Archived Ward guidance assigns no N or P mineralization credit above 20:1; this is a calculation rule, not a universal field threshold [5]. |
| Microbially active carbon (%MAC) | 100 × 24-hour CO2-C / WEOC [7] | An index relating respiration to water-extractable carbon | The two values come from separate analyses. The ratio does not directly measure the fraction of the extracted carbon consumed by microbes. |
| H3A nutrients, where included | Nutrients extracted with the H3A solution [1] | Nutrient concentrations under that extraction method | Use H3A-specific interpretation. Do not apply Mehlich-3, Bray, Olsen, or ammonium-acetate thresholds directly [44] [45]. |
| Soil Health Score / Soil Health Calculation | Formula combining respiration, WEOC, and WEON [1] [5] [8] | A composite indicator for context and monitoring | Check the formula version. A higher score alone does not establish higher yield or lower fertilizer need. |
| Available N-P-K, N credit, fertilizer recommendation | Measured nutrient fractions combined with model assumptions and crop information [1] [7] | The laboratory’s estimated nutrient supply and proposed rate | Ask which equations, depth conversion, yield assumptions, and regional field calibrations support the recommendation. |
Which score formula was used? Published documents are not uniform. The 2018 paper prints (CO2-C/10) × (WEOC/100) × (WEON/10) [1]. Ward’s archived information sheet prints CO2-C/10 + WEOC/50 + WEON/10 [5]; its report-definitions sheet describes respiration divided by organic C:N plus weighted WEOC and WEON [8]. These documents establish a version issue, not which formula every laboratory uses today. Ask the laboratory to identify its current calculation and whether older results can be recalculated before treating a score change as a management response.
The nutrient calculation also has assumptions. In the 2018 paper, potential N mineralization equals the CO2-C:WEOC fraction × WEON × 2.24 × n, where n represents growing-season rain or irrigation events greater than one inch; the paper suggests four as a starting value [1]. Its available-N equation uses 2.24 to convert ammonium-N from mg/kg to kg/ha and 1.6 for nitrate-N, with the latter incorporating an assumed 30% nitrate loss. The 1.6 factor is therefore not a simple increase in measured nitrate. Laboratory guidance may implement credits differently [7]. The biological rationale draws on several studies; the 2008 compost experiment on Houston Black clay is one example, not the entire evidence base [1] [9]. These relationships still need field validation for the crop, region, and recommendation being used.
What have field studies found?
Studies have evaluated several different questions: whether indicators respond to management, whether a score tracks yield, and whether a nutrient recommendation predicts fertilizer response. Success on one question does not settle the others. The studies below show useful biological signals alongside limits in consistency and regional calibration.
Selected evaluations of Haney indicators and related methods, 2016-2025
| Study | Where and how | What it found |
|---|---|---|
| Morrow et al. 2016 [10] | Five long-term trials, inland Pacific Northwest, 2-30 years old | 1-day C mineralization and the Haney index were highly variable (coefficients of variation up to 53% and 37%) and consequently not very sensitive to tillage or cropping intensity; POX-C scored best on the authors' seven criteria |
| Roper et al. 2017 [11] | Three North Carolina trials with 17-32 years of contrasting management | The Haney test rated soil from every system except moldboard plowing as in good health; Cornell CASH rated the same mountain soils low or very low except the no-till organic system, which scored medium; neither test correlated with crop yield |
| Chahal & Van Eerd 2018 [12] | Six-year cover crop experiment, Ridgetown, Ontario, processing vegetables | Haney, Solvita, and SLAN results were inconsistent between years in detecting cover crop effects and in their relationships with yield, soil organic carbon, and a 2-day C-mineralization test. |
| Yost et al. 2018 [13] | 17 corn N-rate trials in eight Midwest states, one season (2016) | The N recommendation with expected yield explained at most 28% of variation in economically optimum N rate. The score and CO2 burst each explained about 55%; the two were strongly related (R-squared 0.98). |
| Chu et al. 2019 [14] | No-till corn-soybean cover crop trial established 2013, west Tennessee | H3A extracted the least P, K, Ca and Mg of three extractants; neither the score nor any component detected a cover crop effect; the Solvita CO2 value did not reliably estimate potentially mineralizable N |
| Bavougian et al. 2019 [15] | Long-term tillage x rotation x N-rate trial, northeast Nebraska | The H3A and water-extract N tests detected more treatment differences than conventional nitrate and had similar precision; high N and intensive tillage mostly gave low burst and score values; yields were generally not correlated with the indicators |
| Singh et al. 2020 [16] | Three Tennessee long-term experiments (39-year tillage, 4-year cover crop, 37-year cotton) | Haney indicators, both score versions and N mineralization responded inconsistently to management; the score was driven mostly by WEON; H3A nutrients were more variable than Mehlich-1 |
| Bagnall et al. 2023, NAPESHM [17] [18] | NAPESHM: 124 long-term North American sites; more than 30 measurements considered across the project | Recommended soil organic carbon, aggregate stability, and 24-hour C mineralization as a minimum suite. The minimum-suite analysis did not directly evaluate the Haney score or H3A nutrient recommendations. |
| Sherbine et al. 2023 [19] | Minnesota cropland, two years of seasonal sampling after tile drainage | No detectable response to recent drainage installation during the study; the biological indices varied with season and year, with the highest values in spring. |
| Hu et al. 2025 [20] | Eight sites in northeastern Colorado: seven dryland cropped fields and one pasture | The score was strongly related to the CO2 burst (r = 0.82). Estimated mineralizable N was not related to the 28-day incubation result (R-squared below 0.01). The pasture had the highest score under both assessment frameworks. |
Management sensitivity was inconsistent in several trials [10] [11] [12] [16]. Nebraska provides a useful positive result: water-extract and H3A nitrogen measurements detected treatment differences missed by conventional nitrate testing, with similar analytical precision [15]. The North Carolina results also prompted a published disagreement about the Cornell CASH indicators [21] [22]. That reanalysis focused on CASH, so its conclusions should not be transferred to the Haney score. For a farm, the relevant question is whether the selected indicator can detect the particular change being monitored.
The North American Project to Evaluate Soil Health Measurements provides broader support for respiration as a monitoring indicator [17] [18]. Its recommended minimum suite combines soil organic carbon, aggregate stability, and 24-hour carbon mineralization. WEOC also responded to management, but overlapped with other carbon measurements [17] [23]. The project’s nitrogen analysis found strong relationships with carbon indicators and suggested organic carbon plus respiration as proxies for N-supply function [24]. This does not supply a field-specific fertilizer credit or validate the Haney score. A separate synthesis of 1,071 samples found that short-term mineralizable carbon and POX-C reflected different aspects of organic matter cycling, supporting their use as complementary indicators [25].
Can respiration help estimate nitrogen need? Research in North Carolina and Virginia found promising relationships between a 3-day CO2 flush and corn response to N [26] [27]. A later analysis across 111 fields explained 46% of variation in yield-scaled optimum N [28]. That method differs from the 24-hour Haney protocol in incubation duration, soil preparation, and rewetting. Its equations and thresholds should not be applied directly to a Haney report. In 29 Corn Belt N-rate trials, better biological soil health was associated with higher yield per unit of N, but the indicators offered limited advance information about a site’s fertilizer response [29].
Method consistency matters. A developer study found strong correlations among Solvita, titration, and infrared CO2 measurements, but correlation does not make their values interchangeable [30]. The manufacturer’s laboratory comparison found substantial effects of rewetting method [31], and an independent study found high between-laboratory variability in mineralizable carbon [32]. NRCS guidance has also evolved since its 2019 technical note [33]; the 2025 note discusses respiration methods lasting one to four days [34]. Keep the method fixed when monitoring, and check with the laboratory before combining results from different protocols. Part 5 explains these differences.
How should the field be sampled?
Build the sampling plan before ordering. Purdue and NRCS recommend consistent locations, depth, seasonal timing, and laboratory methods for repeated comparisons [35] [34]. Record crop, recent tillage and inputs, weather, and soil conditions. Consistency helps distinguish management effects from sampling variation; analytical precision still matters.
- Confirm the depth and sampling design. Ward’s archived Haney protocol specifies 10-15 cores at 0-6 or 0-8 inches for its fertility recommendations [36]. Regen Ag Lab asks for at least ten cores collected at a consistent depth [37]. These are laboratory examples; CEMA 216 has a separate sampling design [38] [48]. Keep different depths separate and use the depth required for the intended interpretation.
- Read a pounds-per-acre credit with its assumptions. Ward’s archived conversion is sample depth in inches × 0.3 × the estimated organic-N-release value in ppm [7]. An estimated release of 30 ppm therefore converts to 54 lb N/acre at six inches or 72 lb at eight inches. This illustrates the report’s arithmetic, not a reason to change sampling depth or a measurement of actual crop N supply.
- Choose suitable field conditions. Avoid extreme wetness, dryness, or temperature, and recent tillage, amendments, or fertilizer unless the sampling design specifically addresses them [38] [39]. Regen Ag Lab recommends soil at least 50 °F [37]. Confirm timing with the receiving laboratory and record departures from the plan.
- Keep samples cool and ship promptly. Laboratory drying and rewetting does not make field handling irrelevant. Follow the receiving laboratory’s storage, shipping, and holding-time instructions [37] [40]. For CEMA 216, obtain the protocol before collection; the current standard calls for cooler or refrigerator storage when samples are not sent immediately, and additional precautions for PLFA [38].
- Choose a repeat interval that serves the question. Annual sampling can build a useful record, but a one-year difference is not enough to establish a management trend. NRCS suggests allowing three to five years, or longer in dry regions, to observe consistent improvement [34]. Purdue discusses a two-year testing interval [35]; program or research requirements may call for more frequent testing, including annual CEMA 216 sampling [48].
Can the nutrient lines support a fertilizer decision?
First identify how the laboratory calculated the credit. Ward’s archived guidance bases organic-N release on the water-extract C:N ratio, respiration, and WEON pool, and caps the credit at the measured WEON pool [7]. Its older information sheet assigns no N or P mineralization credit above a 20:1 water-extract C:N ratio [5]. These are model rules. A line labeled “nitrogen savings” expresses an estimated difference from a nitrate-only calculation; it does not establish realized savings or maintained yield [5].
The 17-site, eight-state corn study found that the Haney N recommendation with expected yield explained at most 28% of variation in economically optimum N rate; the score and CO2 burst each explained about 55% [13]. That supports further investigation of the indicators, while leaving substantial uncertainty in a rate decision. Minnesota Extension also reports cases where Haney recommendations would have increased N rates relative to its guidelines, and advises against using soil health tests alone to determine fertilizer rates [41] [42]. NRCS likewise cautions against using soil health package results for nutrient management planning [34]. If a package includes conventional fertility analyses, confirm that their methods, sampling, and interpretation meet the applicable local guidance.
If a Haney-based N rate would change management, compare it with the locally recommended rate in small, replicated strips before extending it across the farm [43]. Record applied N, yield, and net return with an agronomist. Where locally validated, a pre-sidedress nitrate test can inform an in-season corn decision. A late-season stalk nitrate test answers a different question: it helps assess the season’s N management after most fertilizer decisions have already been made [37]. Neither is interchangeable with a crop-response trial.
For phosphorus and potassium, extraction method is central. Kansas and Tennessee comparisons found that H3A and Mehlich-3 values were related, but conversion errors were too large to transfer existing fertilizer calibrations reliably [44] [45]. Iowa researchers tested H3A phosphorus against crop response and found weaker relationships than for Bray-1 and Mehlich-3 in those trials [46]. This is evidence for using method-specific, regional calibration; it does not show that H3A can never be calibrated. Wisconsin Extension makes the same practical distinction between measuring a nutrient and establishing a fertilizer recommendation [47].
H3A versus the calibrated extractant: what three states found
| Study | Soils | H3A compared with Mehlich-3 (or routine tests) | Authors' conclusion |
|---|---|---|---|
| Rutter & Ruiz Diaz 2020 [45] | Kansas | r = 0.90 (P) and 0.91 (K); Mehlich-3 extracted about 25% more P and 250% more K; RMSE 15.4 ppm P, 83.4 ppm K | Errors too large to plug H3A values into existing Kansas calibrations |
| Adotey et al. 2025 [44] | Tennessee | R-squared 0.87 (P) and 0.39 (K); Mehlich-3 extracted about 60% more P and 25% more K | Inappropriate to estimate Mehlich-3 P and K from H3A-4 for fertilizer recommendations |
| Mallarino & Jones 2018 [46] | Iowa, 24 sites, 54 corn and 58 soybean site-years | R-squared 0.94-0.95 with Bray-1 and Mehlich-3, 0.97 with Olsen; yield-response model R-squared 0.33-0.40 (H3A) vs 0.60-0.73 (Bray-1, Mehlich-3) | H3A needs its own field calibration; preliminary critical ranges 12-16 ppm corn, 14-19 ppm soybean |
Does the package meet CEMA 216 requirements?
Check the current standard and job aid with the Qualified Individual (QI) before ordering. The national documents listed by NRCS as 04-2026 require tests for five processes: aggregation, carbon cycling, microbial activity, carbon food source, and nitrogen food source, plus pH and texture [38] [61]. The standard lists WEOC and WEON as alternate methods for the two food-source categories; the April 10, 2026 FAQ explicitly explains their connection to the Haney method [48]. A 24-hour respiration test can address microbial activity. The Soil Health Score and H3A nutrient credits do not substitute for the required analyses.
A Haney package may therefore supply several required measurements, but the name alone does not establish compliance. Confirm aggregate stability, the accepted organic-carbon method, texture, pH, and every other required method on the actual order. The QI must also arrange the pre-work conference and meet sampling and reporting requirements [38] [61]. The FAQ describes an instance as three separate composite samples, each made from five subsamples, and estimates about $150 per sample before shipping [48]. Confirm the current laboratory qualifications and contracted requirements with the local NRCS office. SHE’s CEMA 216 guide covers the full workflow.
What does the price include?
Compare package contents as well as price. Regen Ag Lab lists its Haney package at $60, while Ward lists a $61.90 Soil Health Assessment with different nutrient extraction methods [52] [51]. The examples below were checked on September 17, 2026. Prices, turnaround, and package contents can change; request the current specification before ordering.
Examples of soil-testing options and posted prices
| Test or package | What it adds | Useful decision or question | Posted price per sample |
|---|---|---|---|
| Haney package | Respiration, water-extractable C and N, H3A nutrients, and calculated indicators | Monitor biological indicators and investigate nutrient cycling | $60 Regen Ag Lab, schedule effective Jan. 1, 2025 [52]; $65 Midwest Labs Soil Health Complete, including conventional S3C fertility analyses, undated [53] |
| Ward Soil Health Assessment | Respiration and water-extractable C/N; conventional nutrient extracts; modified aggregate stability | Combine biological monitoring with the listed chemical and physical measurements | $61.90, effective Jan. 1, 2026. The current listing specifies Mehlich-3 P and ammonium-acetate cations, rather than H3A [51] |
| Routine fertility panel | pH, extractable nutrients, and other analyses depending on package | Locally calibrated lime and fertilizer decisions | $17.35 S-1 to $23.65 S-4 at Ward; organic matter is not included in S-1 [51]. Midwest S1A $9.77 and S3C $26.78 without recommendations; $11.03 and $27.83 with recommendations [53] |
| 24-h CO2 burst alone | The respiration line only | Track potential microbial activity with a consistent protocol | $29.70 Ward, 2026 [51]; $25 Regen Ag Lab, individual-test list dated Aug. 28, 2025 [52] |
| POX-C (active carbon) | Permanganate-oxidizable carbon | Track a management-sensitive carbon fraction; an approved CEMA 216 method | $23.65 Ward, 2026 [51]; $25 Regen, 2025 [52]; $30 Cornell, undated [54] |
| ACE protein | Autoclaved citrate-extractable protein | Assess a protein-related organic-N indicator; an approved CEMA 216 method | $23.65 Ward, 2026 [51]; $30 Cornell, undated [54] |
| Wet aggregate stability | Water-stable aggregates | Structure; a CEMA 216 required indicator | $35.75 Ward, 2026 [51]; $30 Regen, 2025 [52]; $30 Cornell, undated [54] |
| PLFA | Microbial community biomass and composition | Estimate broad microbial groups and biomass; it does not directly measure their field functions | $100.95 Ward, 2026 [51]; $90 Regen, 2025 [52] |
| Cornell CASH | Physical, biological, and chemical indicators; selected scores adjusted for texture | Assess several soil functions using the framework’s reference groups; interpret regional fit | Basic $100, Standard $140, Standard PLUS $160; 5 cups; typical turnaround 4-8 weeks. Standard predicts ACE protein; Standard PLUS measures it [55] [56] |
| CEMA 216 core package | The five required processes plus pH and texture | NRCS cost-shared baseline and follow-up testing | $149.50 Ward [50] [51]; $180 Cornell [55]; $150 UVM [57]. The March 2026 MCCC compilation has differing contents; its $93.01-$103.01 entry excludes aggregate stability [49]. |
Five interpretation checks
- Is the comparison fair? Soil, climate, and management history influence indicator values. Use comparable sampling areas and methods rather than ranking unrelated farms by raw scores [7]. Cornell’s framework uses texture groups for selected indicators, but a scoring framework still needs regional context [58] [59].
- Is there a sustained change? Compare several observations and their sampling records. A single increase or decrease can reflect season, weather, or recent inputs [19] [35].
- Does the score answer the farm question? A management-sensitive indicator is not automatically a yield predictor. North Carolina trials found limited discrimination among some long-term systems and no correlation between the tested soil health assessments and yield [11] [59]. Keep crop performance and field observations alongside the laboratory record.
- What has not been measured? The core Haney indicators do not directly measure infiltration, bulk density, or water-holding capacity [7]. Use field observations and targeted measurements to investigate rooting, compaction, and water movement [34]. Distinguish inherent context, such as texture, from management-responsive conditions, such as pH.
- Whose benchmark is being used? Ward’s archived “above 7” guidance is a laboratory interpretation, not a universal pass mark [5] [7]. Purdue notes that the Haney calculation has no defined “high” threshold [35]. A nearby perennial reference area can provide context when soil and landscape position are comparable, but it is not automatically an attainable cropping-system target [60] [34].
Before the next sample
Write down the decision the test should support, then confirm the laboratory’s package, methods, and handling instructions. Save the component results and score formula with the sampling record. If the report suggests a different fertilizer rate, review its local evidence with an agronomist and plan a field comparison. On the next sampling round, return to comparable locations and conditions so the record becomes more useful over time.