The commonly used method is to install static gas chambers in the field, from which gas samples were periodically collected using a syringe inserted into the chamber and transfer the sample in the vials. The vials are then arranged in a tray and gas concentrations are measured using gas chromatograph. The method can measure all there GHGs (CO2, N2O, and CH4) simultaneously in one gas sample.
Probably there is no best method, I worked with closed chambers in the field, it works for comparative values between sites in a landscape, less for absolute values. See for instance https://dl.sciencesocieties.org/publications/sssaj/abstracts/72/2/331
Some alternative analytical methods are referred at the end of an article downloadable at http://afrsweb.usda.gov/SP2UserFiles/person/31831/2009VentereaetalSSSA.pdf
Best,
You may find the publication by Ambus et al. (2006) in the Biogeosciences, 3, 135 - 145 useful. The method used can be tried on fertilized farms to obtain N2O emissions. Several other methods can also be obtained from the literature depending on the objectives of the study. Good luck!
The use of closed chambers (which are fairly inexpensive and can be made in-house) is probably the only method. We once used for N2O and CH4 emissions following cattle slurry application. We used on-site portable gas analyser. The issue is how one accounts for the variability across a field, let alone landscape. Extapolation based on a few measurements can be highly misleading, as N2O emissions are likley to be variable due to varibility in soil conditions (moisture, labile organc C, oxidised and non oxidised N). However the reliability of such measurements can be improved by making more measurements across the field.
We sample gases with a gas-tight syringe and inject gas samples into an evacuated vials. Vials are prepared before sampling by filling with UHP-grade helium and purging (by vacuum) several times, with the purge being the last step. This filling-purging aims at removing any residual N2O from vials. This works quite well. Vials can be reused if a QC/QA protocol of is followed. We use an SRI 'greenhouse gas' GC for analyses. Method detection limits are reasonable for N2O emissions from soils.
The commonly used method is to install static gas chambers in the field, from which gas samples were periodically collected using a syringe inserted into the chamber and transfer the sample in the vials. The vials are then arranged in a tray and gas concentrations are measured using gas chromatograph. The method can measure all there GHGs (CO2, N2O, and CH4) simultaneously in one gas sample.
In terms of gas sampling, I'm currently using stainless steel stakes, with machined cavities going down at regular intervals. A plastic membrane (we use cling film) goes over the cavities to prevent water seeping in, a stainless steel plate is screwed on top to prevent the membrane tearing. The plate has 6 pin holes over each cavity in a 5 point star pattern to allow for sampling using a gas tight syringe. You hammer the stakes into the ground, leave them for ~48 hours to equiliberate with the surrounding soil's gas concentration, then take them out, sealing them with black electric tape to prevent leakage when you take it back to the lab. You can then sample the wells with a syringe and inject directly into a GC. This will give you a depth profile of your target gas.
Paper in the link has the schematic for the stake http://www.sciencedirect.com/science/article/pii/0734242X9090049S
I'm not sure about alternatives to GC though, considering GC is pretty much the gold standard.
I assume that you want to measure N2O exchange between the soil and the atmosphere and not N2O concentrations in different soil depth. As already mentioned static closed manual or dynamic closed chambers automated chambers are the most common methods used. All have different sources of error and their individual advantages and disadvantages.
A great source of information on different chamber designs and how to sample and to calculate fluxes can be found for example in following publications with a lot of examples:
http://www.ars.usda.gov/research/programs/programs.htm?np_code=212&docid=21223&page=2
www.ars.usda.gov/SP2UserFiles/Program/212/Chapter 3. GRACEnet Trace Gas Sampling Protocols.pdf
http://www.n2o.net.au/templates/n2o/documents/Methodology_Guidelines_Final-2013.pdf
http://www.n2o.net.au/index.php/data/how-to-guides/how-to-manual-greenhouse-gas-sampling
Depending on the chamber method used (closed dynamic or closed static) different analysers can be used in combination with the chambers: GC, TDL, or Photo acoustic sensors as well as FTIR. If you don't have a mobile GC or any of the other analysers available manual gas sampling of chamber headspace air with syringes into vials is probably the most commonly used method.
TDLs and FTIRs can also be used for Eddy Covariance type measurements to integrate over larger landscapes and open path FTIRs can be used to measure N2O flux horizontally...
We measure N2O flux from soil with closed chambers from Klaus Butterbach-Bahl, KIT Germany (http://imk-ifu.fzk.de/staff_Klaus_Butterbach-Bahl.php). This system works perfectly!
If its the gas in the soil you want to measure rather than the emissions from the the soil surface you can make probes using gas permeable water tight membrane (e.g. Accurel). The air inside the membrane equilibrates with the soil and then a sample can be collected and analysed on the GC.
If you would like to measure N2O in the soil profile (saturated or unsaturated soil), I suggest to use diffusive equilibration samples contructed of silicone tubing. They can easily be self-made using cheap materials. You may have a look here: Goldberg, S.D., Knorr, K.-H., Gebauer, G. (2008): N2O concentration and isotope signature along profiles provide deeper insight into the fate of N2O in soils. Isotopes in Environmental and Health Studies, 44 (4), 377-391
The static gas chambers is most commonly used for measurements of GHGs from the fields.
Im starting my work on greenhouse gas emissions in smallholder vegetable production systems in Zimbabwe. What is the minimum number of gas chambers should I have per plot or what are repeated measurements in GHG work?
- Badges
- Science topic
- Similar topics
- Agriculture
- Soil Science
- Soil