I´m a PhD student in Geoscience and Natural Resource Management. I´m sampling soil down 2 meters depth and investigate how much carbon there is at that depth. Can anybody suggest the newest method to determine soil carbon content?
To choose the best procedure you must consider what type of soil do you have in your study area. If your soils have carbonates, you must to be sure that your technique is estimating total organic carbon rather than total carbon. Carbonates are common under arid and semiarid ecosystems in increase greatly at depth. At least you were interested in also considering inorganic carbon. Anyway always is useful to know what kind of carbon you are sampling, since they are related to different soil processes. Hope this helps.
Split you sample in two. One part go for LOI at 550 °C 2h. Then, you put both parts in the C/N analyzer and subtract the C measured for the LOI sample (C coming from carbonates) from the C measured for the other sample (total C) and you get the organic C.
A review paper on soil carbon analysis is available " Protocols for soil carbon " in this research article the author figure out different protocols for soil carbon analysis please search this paper on Google it will help you. This best and accurate method for SOC analysis is Walkley and Black method
Take into account that Walkley-Black is a semiquantitative method (partial oxidation of the sample). This method was/is mainly used for soil classification. To work up to 2 m depht, a CHN determination is better. Anyway you could split any sample, collected according to the genetic horizons, in two subsamples; you can use the Walkley Black to classify your soil and the CHN determination to get more precise data.