I want to estimate the rate of soil respiration in the Hyrcanian forest by following the protocol of placing series of 20 gr soil (stored in the fridge) into series of jars. Then I put 20 ml (0.2 Molar) of NaOH in each vial and all of them were placed individually in separate jars, also, all of them were sealed completely. After 7 days I opened the jars and added 2 ml (0.2 Molar) BaCl2 into the vials and then added 3 drops of phenolphthalein until it became purple and then I added HCl (0.1 Molar) until it became white!
The point is my result does not seem correct and the amount of acid that I used for my titration in the control sample is fewer than some of my other samples and this feels absolutely wrong. Does anyone have a suggestion and advises for me to estimate soil respiration in my research?
There nothing seems to be wrong with your protocol. Anyway, you should keep in mind that soil moisture content and temperature are the most important abiotic factors which influence soil respiration. You also might consider differing amounts of organic matter.
Your jars should be sealed gas-tight. You could check each of them by running your experiment without soil. This has the advantage (1) that you can identify outliers/ possibly leaking jars and (2) to get an idea about your blank values and your method error.
I fully agree with Dr Fisher observations, there is nothing wrong in your procedure. Soil respiration is commonly estimated as the flux of CO2 emitted from the soil being measured with chambers using chemical traps for absorbing ( usually a KOH or NaOH solution) was then determined by titration. Generally residual NaOH is titrated with HCl to determine the CO2. NaOH traps should be in closed incubation Jar , which should be sealed airtight. You have to be assured that. We are also find some variation when moisture content are not similar in all the Jars.
OTHERWISE I find Automated Gas Analyzer is the better method if you have the facilities.
Dear Dr Fisher and Dr Tarafdar
I checked my method with garden’s soil and the results seem to be okay, but this method is not working on my forests soil unfortunately, and I should mention that the amount of water in each jar are different with each other (some of them are saturated with water and others are dry) and I sealed all the jars carefully so I am sure that the error is not because of leaking and moreover, I keep them in big box that is far from the light in corner of the room and each time I use 2 control sample. Do you think it is better to apply air-drying and then add them a little water? I don’t know what is extra or missing in forest’s soil that makes this method invalid.
I think you may go for air drying and then maintain the soil moisture content uniformly may be between 50 and 75% .
Your method is fine , though many pottential human errors may accure in this method. At first I woud suggest to change your method if it is possible.
I have faced the same issue in my master project. My problem was that I used diffetent NaOH (same brand) in the jars as the first one was insuficient for all the sampel. An the second NaOH was not as pure as it was labled.
My suggestion is to make sure you use same (same bottle) NaOH and HCl or alternatively check the pureity of both by acid and base tiration.
Good Luck.
Dear Iman
which method do you suggest for forest respiration? I think as you know, Iranian university does not support properly students for Providing equipment and financial support and I think maybe this is the easiest way for me for analyzing respiration and moreover, I use the same primary substances for my all samples.
Regards,
Hellia
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