Soil Respiration 1-Day CO2 Burst Interpretation Guide

PDF of information below: Soil Respiration 1-Day CO2 Burst 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 www.wardlab.com and new information may be added as it becomes available.  Any questions regarding soil health testing may be directed to Lance Gunderson at Lgunderson@wardlab.com