I am working on a soil organic carbon and total nitrogen data from a low N input dryland environment, and I found the C:N ratio as smaller; 6 in 30-60 cm. To me its very low since these systems do not receive more than 45 kg N/ha, and I am wondering how low it can be in soils?
It is not strange to have a low C:N ratio in the lower horizons. One of the reasons could be due to the fact that carbon content normally decreases with depth in most soil profiles, Another reason may be related to nature of the soil colloids. If the latter are mostly negatively charged, then more nitrogen in the form nitrates will be found in the lower horizons. If this were the case, then the C:N ratio will definitely be low in the lower horizons as a result of its high mobility in such soils. As to how low the C:N ratio could be will depend on the nature of the soil in question and the microbial activities that take place in this soil.
Hi Rajan,
those are really quite low CN ratios. The lowest i ever found were around 8 in a boreal forest subsoil. In theory the CN of soil can get as low as the CN of the microbial biomass. CN of bacteria can be as low as 5 so I think that's also the lowest you can find for SOM. For more on that you can take a look at Rumpel and Kögl-Knabner (SBB 2011) and the citations therein.
Good luck
Hi Rajan,
I found in the soil surveys from my province (Cordoba, Argentina), argillic horizons with C/N < 3 (> 60 cm depth). In 30-60 cm there are values around 6 in some soil series
Thank you all, the reason I was surprised was because I did not expect much N leaching in semi arid ecosystem (
N leaches as NO3- which is a minimal fraction of total N. Remember that around 98% of total N is organic N.
I guess you are talking about C/N ratio considering organic material, otherwise many other factors may bring this ratio to an unthinkable level. as Schnecker pointed out, microbial activity is the main driver of this ratio.
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