Soil Respiration Test

The Soil Respiration 1-Day CO2-C test represents the amount of CO2-C (ppm) released in 24 hours from soil microbes after your soil has been dried and re-wetted (as occurs naturally in the field). This is a measure of the microbial biomass in the soil and is related to soil fertility and the potential for microbial activity.

General Information

Soil is a complex ecosystem that provides a habitat for an endless array of micro and some macro organisms. These include bacteria, fungi, protozoa, nematodes, earthworms, etc. These organisms are responsible for much of the nutrient cycling that takes place in the soil. They decompose crop residues, store plant nutrients, create stable organic matter in the form of humic acid, and help build soil structure. This leads to reduced soil compaction and erosion, while increasing water holding capacity and a deeper root zone. The relationship between different microorganisms and plants is dynamic. The predatory action of protozoa on bacteria helps release nitrogen into the soil and symbiotic bacteria and fungi aide the plant in acquiring more nutrients. Through better understanding of soil microbial communities we can begin to allow these organisms to work for us in our goal of high yielding, sustainable agriculture.

Many microorganisms give off carbon dioxide (CO2) as a result of aerobic respiration. The Soil Respiration 1- Day CO2 Burst test quantifies the amount of respired CO2 after rewetting a dry soil sample, employing an infrared gas analysis (IRGA) technique. The amount of CO2 measured over a 24 hour period represents “active carbon” or “respirable carbon” that was acted upon by the microbes and may also be used to estimate potential mineralizable nitrogen and phosphorus from the soil organic matter. Soil microbial biomass plays a critical role in controlling the supply of nitrogen and phosphorus to crops. The turnover and activity of soil biomass may account for more than 50% of the total crop nitrogen uptake. Therefore, the rate of soil biological activity should serve as a reliable index of the soil’s capacity to supply nitrogen, and perhaps other nutrients such as phosphorus, to crops. Studies in the past 10 years have shown the flush of CO2 following drying and rewetting of soil mimics some natural processes and characteristics of long-term incubations and has been observed to correlate with nitrogen supply potential. The quality of soil carbon (C:N ratio) and supply of nutrients and moisture will have a significant effect on the exact ratio of biomass measured as evolved CO2 and nutrient release.

In general, soils that exhibit a higher CO2 flush are considered to contain greater microbial biomass due to a more favorable food supply, leading to an increased potential for activity and nutrient turnover/mineralization. Management practices employing no-till, manure, and cover crops help increase the amount of quality food available to microorganisms and the soil respiration test allows producers to track such changes over time in response to management. In addition, soil respiration has been incorporated into other testing procedures such as the Rick Haney’s Test, which provides a more comprehensive measure of soil health using respiration as one of the test’s foundations.

Additional information is available on the website at and new information may be added as it becomes available. Any questions regarding soil health testing may be directed to

PDF: Respiration Information

Sampling Information (H3A)

Listed here are general guidelines to sample for the Respiration 1-Day CO2 Burst:

If combining Soil Respiration analysis with PLFA, please refer to the PLFA sample submittal instructions and follow those guidelines for submitting one sample for both tests.

  1. Use a standard soil core sampler, drill corer, or spade to obtain a furrow slice soil sample.
  2. Take 10-15 cores either 0-6 or 0-8 inches deep. We do not recommend running the Respiration Test
    on samples taken at alternate depths or sub soils. We can perform the test, but the results will not
    necessarily reflect the majority of the soil microbial biomass.
  3. Combine all the cores, preferably in a plastic-lined paper soil bag, to make one composite sample.
  4. Add all sample identification information you need to the sample bag and ship the samples in a regular box.
  5. Mark each sample and the shipping container Respiration 1-Day CO2 Burst, or Soil Respiration Test to ensure proper handling on our end.
  6. Include any paperwork and soil submittal forms that will allow us to identify the customer/grower and the tests desired. If you are a new customer, please also include a physical address, phone number, and email address (if applicable) so we can set up your customer account.
  7. Samples can be mailed to or dropped off at Ward Laboratories Inc, 4007 Cherry Avenue, Kearney, NE 68848. When mailing samples it is best to send them overnight if the temperatures are very hot.

Additional information is available on the website at and new information may be added as it becomes available. Any questions regarding soil health testing may be directed to

PDF: Respiration Sample Information

Report Example (PDF)

Interpretation Guide

PDF: Interpretation Guide

Soil Respiration:

The respiration test is aimed at measuring the amount of CO2-C a soil can produce over a 24hr incubation period following a significant drying and rewetting event.  In other words, how much does your soil breathe when conditions are optimal?  Most microbes produce CO2 through aerobic respiration just as we do and the more CO2 a soil produces the more life it contains or the higher the microbial biomass.  This is important because it relates to a soil’s potential for microbial activity, which is tied to many functions of a healthy soil such as nutrient cycling, soil aggregate and organic matter formation, disease suppression and stimulation of plant growth.

Soil respiration readings can fall anywhere from near zero to 1000 ppm of CO2-C.  However, most agricultural soils are currently degraded and do not read above 200 ppm.  In general, the higher the number the better, but this can have an effect on subsequent management decisions.  For example, a soil with a very low score may exhibit symptoms of slow residue breakdown.  On the other hand, residue may cycle very quickly in a soil with a high score.  Therefore, residue management strategies and the soil respiration score one might strive for are going to be dependent on the type of production system you find yourself in.

Below is a table showing the rankings as they relate to soil respiration.  These rankings are based on my own observations and the observations shared with me by others.  While I feel that these descriptions fit a lot of different production scenarios, they will not necessarily fit each unique situation.  In any case, however, soil respiration is considered a strong indicator of overall soil biological function.

Soil Respiration Ranking Table:
CO2-C in ppm Ranking Implications
0-10 Very Low Very little potential for microbial activity; slow nutrient cycling and residue decomposition; high carbon residue may last >2-3 yrs. with limited moisture; Nearly no N credit given; Additional N may be required due to microbial immobilization
11-20 Low Minimal potential for nutrient cycling; residue management can still be a problem; Very little to no N credit given
21-30 Below Average Some potential for nutrient cycling; residue management can still be a problem with prolonged use of high carbon crops; Little N credit given
31-50 Slightly Below Average Low to moderate potential for microbial activity; Some N credit may be given
51-70 Slightly Above Average Moderate potential for microbial activity; Moderate N credit may be given; May be able to start reducing some N fertilizer application
71-100 Above Average Good potential for microbial activity; Moderate N credit may be given depending on size of organic N pool; Can typically reduce N application rates
101-200 High High potential for microbial activity; more carbon inputs may be needed to sustain microbial biomass; moderate to high N credit from available organic N pools may be given; N fertilizer reduction can be substantial
>201 Very High High to very high potential for microbial activity; residue decomposition may be <1 yr.; keeping the soil covered could be a problem in some systems; high potential for N mineralization and N credits from available organic N pools may be given; N fertilizer reduction can be substantial

You will notice that no ‘true’ average is given in the table above because the rankings are on a sliding scale and are somewhat dependent on soil type and climate region.  Soil and farm management does, however, influence soil respiration scores regardless of what type of soil and climate one has to work with, but much like yield potential, we must work within reasonable expectations for a given area.  In general, cold or arid climates and/or sandy or extremely high clay soils will not usually perform as well as regions with abundant moisture and/or a longer growing season.  For example, a soil that has a respiration reading of 50 from New Mexico might be interpreted as above average or even high for that region.  Whereas a soil that scores the same from central Iowa might be interpreted as below average for that region.  A soil that scores below 10 or above 200 is considered to be very low or very high, respectively, regardless of these other aforementioned factors.

Soil respiration values can change with the growing season and environmental conditions.  The variability or swings in respiration values are typically greater in poor to marginal soils due to these soils having less ability to buffer against disturbance and times of fewer carbon inputs such as fallow periods.  On the other hand, soils that are healthier often exhibit the ability to sustain a higher microbial biomass or respiration value during times of drought or extreme temperature.  In other words, a healthy soil becomes more resilient to environmental conditions and disturbance.  In either case, it is important to sample at the same general time each year or at least under the same general soil conditions, especially when tracking change in soil respiration over time as indicator of overall progress.

Additional information is available on the website at and new information may be added as it becomes available.  Any questions regarding soil health testing may be directed to


  1. Franzluebbers, A.J., R.L. Haney, and F.M. Hons. 1999. Relationships of chloroform fumigation ±incubation to soil organic matter pools. Soil Biology and Biochemistry 31:395-405.
  2. Franzluebbers, A.J., R.L. Haney, C.W. Honeycutt, H.H. Schomberg, and F.M. Hons. 2000. Flush of carbon dioxide following rewetting of dried soil relates to active organic carbon pools. Soil Science Society of America Journal 64:613-623.
  3. Haney, R.L., F.M. Hons, M.A. Sanderson, and A.J. Franzluebbers. 2001. A rapid procedure for estimating nitrogen mineralization in manured soil. Biology and Fertility of Soils 33:100-104.
  4. Haney, R.L., W.F. Brinton, and E. Evans. 2008. Soil CO2 respiration: Comparison of chemical titration, CO2 IRGA analysis, and the Solvita gel system. Renewable Agriculture and Food Systems 23:1-6.
  5. Haney, R., W. Brinton, and E. Evans. 2008. Estimating soil carbon, nitrogen, and phosphorus mineralization from short-term CO2 respiration. Communications in Soil Science and Plant Analysis 39:2706-2720.
  6. Haney, R.L., A.J. Franzluebbers, V.L. Jin, M-V. Johnson, E.B. Haney, M.J. White, and R.D. Harmel. 2012. Soil organic C:N vs. water-extractable organic C:N. Open Journal of Soil Science 2:269-274.