Microanalysis would be the technique to employ. Take a small sample of material before and after the process and subject the sample to complete combustion, the carbon dioxide and Nitrogen formed are detected and quantified by an elemental analyser (normally a unit that burns the sample and then separates the gases by GC) This will give you a wt% of C and N in your sample, which lets you work out the Ratio before and after the process..

That is strongly dependent on what kind of samples you have.  You could use nuclear scattering techniques, or even particle induced gamma-ray emission (PIGE). These techniques can be non-destrutives, by the way.

I would say the most common would be Total Kjeldahl Nitrogen and Loss on ignition for C, or run the sample through any CSN such as a Leco

Thank you for your answers. These really give me ideas on how to do this. Points out where I should start. Thank you!

Virginia! you found very good answers and techniques provided by experts. These will help you a lot to plan your work.

You just take representative samples of your organic material but you need to duplicate the sample. Then you take the samples to the laboratory for C  and total N  analysis using appropriate laboratory procedures. Generally, ignition and Kjedahl methods are used for C and total N analysis, respectively. The C/N ratio will be obtained by dividing C content by N content of your organic material.  

Working out the C:N ratio of composts is ok  , but what about the C:N ratio of composting materials where  initial C:N ratio  would be so high,  may be upto 500/600:1, depending upon the source of the materials to be composted. Will the estimation of C through loss on ignition   give reproducible results?

I agree with Michael Brian Harman. most used are Total Kjeldahl Nitrogen and Loss on ignition for C... then you just calculate the ratio.

best regards

Hello Virginia,

One aspect not so far addressed is that the materials are typically heterogeneous so you will need to develop and test a smapling protocol that will almost certainly involve taking large quantities of material and grinding it to get a representative sample.  The previous suggestions regarding C and N testing are OK.

Paul. 

I think there are loads of published data on this aspect that can reliably be used as reliable estimate of C:N of agricultural raw material for composting. Analysis of the raw material can  only improve the accuracy of estimate,  bearing in mind the difficulties to obtain representative sample of the lot. By the way, the ash % (minerals) is also a determining parameter.

Consequently, I believe more effort should be geared towards  optimising operational conditions such as pH, temperature, humidity, microorganism loads and so on that are conducive or limiting to adequate composting .The objectives being  to improve quality and quantity of compost produce, and also keeping nutrient losses to a minimum and mitigating environmental impact of composting such as greenhouse gas emission.

Thank you Mr. Jean Pierre Paul. That's actually what we are doing. We are trying to optimize the process of composting with earthworms so the resulting composts will have consistent quality. However, I am inexperienced in this field, so I'm trying to look in all corners. 

Dear Virginia

Grass clippings and other green vegetation tend to have a higher proportion of nitrogen (and therefore a lower C/N ratio) than brown vegetation such as dried leaves or wood chips. If your compost mix is too low in nitrogen, it will not heat up. If the nitrogen proportion is too high, the compost may become too hot, killing the compost microorganisms, or it may go anaerobic, resulting in a foul-smelling mess. The usual recommended range for C/N ratios at the start of the composting process is about 30/1, but this ideal may vary depending on the bioavailability of the carbon and nitrogen.

To calculate the carbon content given C/N and percent nitrogen, solve:

%C = %N x C/N

You may be able to measure the carbon and nitrogen content of your own materials and then calculate the ratio directly.

You can also calculate the C/N ratio online from here:

http://compost.css.cornell.edu/calc/2.html

Regards,

Ata

 Interesting discussion ....

Please find enclosed  some documents , how to calculate  C  N ratio of compost or composting materials ..

First determine Total C and Total N concentration in your samples by following standard analytical methods. Then compute C:N ratio in the samples.

C/N Ratio

Tom Richard and Nancy Trautmann

Once you have calculated the moisture content of your compost mixture, the other important calculation is the carbon-to-nitrogen ratio (C/N). Grass clippings and other green vegetation tend to have a higher proportion of nitrogen (and therefore a lower C/N ratio) than brown vegetation such as dried leaves or wood chips. If your compost mix is too low in nitrogen, it will not heat up. If the nitrogen proportion is too high, the compost may become too hot, killing the compost microorganisms, or it may go anaerobic, resulting in a foul-smelling mess. The usual recommended range for C/N ratios at the start of the composting process is about 30/1, but this ideal may vary depending on the bioavailability of the carbon and nitrogen. As carbon gets converted to CO2 (and assuming minimal nitrogen losses) the C/N ratio decreases during the composting process, with the ratio of finished compost typically close to 10/1.

Typical C/N ratios and nitrogen values for many kinds of compostable substances can be looked up in published tables such as Appendix A, On-Farm Composting Handbook. Some additional nitrogen and ash data is in the table of Lignin and Other Constituents of Selected Organic Materials. (A No-Frames version of the Table of Lignin is also available.) To calculate the carbon content given C/N and percent nitrogen, solve:

%C = %N x C/N

You may be able to measure the carbon and nitrogen content of your own materials and then calculate the ratio directly. Soil nutrient analysis laboratories or environmental testing laboratories can do the nitrogen test, and maybe carbon as well . Your local Cooperative Extension office can give you the names of soils laboratories in your area. The Cornell Nutrient Analysis Lab has information about their procedures for total carbon, organic carbon, and total nitrogen analysis. You can also estimate the carbon content from ash or volatile solids data if either is available.

Good day, sir Behzad Zare

I want to know how do I determine or measure the carbon and nitrogen content of my own materials? Thank you.