Measuring CO2 Production Using Soda Lime:

Data Form for Samples


For use with Protocol 8c: Measuring the rate of CO2 production

Complete this form for each soil sample.


Name(s)  ______________________                     Today’s Date  __________________


Soil sample ID number ___________           Sampling Date  _________________


Soil sampling location ___________________________________________________


Type of area sampled (such as forest or field) ________________________________


Soil description_________________________________________________________




Date and time soda lime incubation started  ______________________


Date and time soda lime incubation ended  _______________________


Total # days incubation (should be 2 days) ________



Protocol 8c, Part 2: Prepare Soil Samples


Before Incubation:


Weight of container (without lid) (G)


_____________ g

Weight of container (without lid) and soil (H)


_____________ g

Total soil weight (I)


H – G = _____________ g



Protocol 8c, Part 3: Prepare Soda Lime


Before Incubation:


Weight of petri dish bottom


_____________ g

Weight of dish and soda lime before drying


_____________ g

Weight of dish and dried soda lime (J)


_____________ g


Protocol 8c, Part 5: Calculate the Amount of CO2 Produced


After incubation and re-drying of the soda lime:


Weight of dish and soda lime


_____________ g

Weight of dish and soda lime

after re-drying (K)


_____________ g

Sample soda lime weight gain (L)


K – J = _____________ g


Calculating the rate of CO2 production:


1) Calculate the corrected weight gain for soda lime:


Corrected soda lime wt gain


Sample soda lime wt gain

Blank soda lime wt gain





________ g


_______ g


______ g



The answer will be in grams of CO2 produced. For use in the final equation, you’ll need to convert this to milligrams:

_________ g x 1000 mg/g = ____________mg CO2



2) Calculate the dry weight of the total soil sample (using soil weights from this form and % moisture from Part 1, Step 6 on the Data Form for Soil Moisture Content):


Dry weight = total soil wt – (moisture content x total soil wt)


Z = I – (moisture content x I)


____ g = _____ g – (______  x  ______ g)


This answer will be in grams of dry soil. For use in the final equation, you’ll need to convert it to kilograms:

_________ g x 0.001 kg/g = ____________kg dry soil



3) Calculate the rate of CO2 production in terms of milligrams CO2 produced per day per kilogram of dry soil. Use your answers from the previous two steps in place of the Xs in this equation:


CO2 production rate = _Y mg CO2 x 1.69/2 days = __________ mg CO2/day/kg dry soil

                                     Z kg dry soil 


Note: If your exposure time was not 2 days, replace the 2 in this equation with the correct # days.

Measuring CO2 Production Using Soda Lime:

Summary Data Form

Use this form to compile results from all of your samples.


Name(s)  ______________________             Date  ______________________

Date soil samples were collected  __________________________________________


Describe the soil or compost samples listed on this page. Include soil sampling location, a description of the location, and any other useful information (such as sampling depth, or observations about soil conditions at the sampling site).






If you carried out an experiment using treatments, such as worms vs. no worms, describe your treatments here.






Summarize your data in the table below (this may include relevant data from other students as well as your own). Use the numbers that you calculated on the Data Form for Samples to fill in Columns 2-4. The final column is for display of mean CO2 production rates among replicate samples. If you carried out an experiment with treatments, then you will calculate separate means for each treatment. 

Sample ID #

Treatment or type of sample


soda lime

weight gain

(mg CO2)

Total sample dry weight


CO2 production rate

(mg CO2/day/

kg dry soil)

Mean CO2 production rate

for replicates (mg CO2/day/

kg dry soil)

















































Interpretation of the Results


1.      Describe the general results of the soda lime experiments. What did you learn about CO2 production rates in your samples?






2.      Were CO2 production levels higher or lower than you expected for each type of sample or treatment? Explain.







3.      If you had replicates of the same type of soil or compost, did you see much variability between these replicates? Explain what you think caused any variability that you found.






4.      If you measured CO2 in different treatments (e.g., presence or absence of worms), explain your results. Which treatment had higher levels of CO2 production? What are some possible reasons for the differences?






5.      If you had a chance to do a follow-up experiment, what would you do differently based on what you have learned? For example, can you think of other treatments that would be useful to investigate?






6.      Why is it useful to measure decomposition rates in soil or compost?