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
Y	=	L	–	C
________ 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

Corrected soda lime weight gain (mg CO2)

Total sample dry weight (kg)

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?