The total carbon content of soil is a hot topic at present, with much discussion on how much there is, how much there should be, and how much can actually be absorbed – the latter being a figure that may not always correspond to general expectations.
What is not as talked about is in what form that carbon is.
It is the division between inert carbon and microbial carbon that is difficult to assess, yet has the potential to be another measure for soil health.
Microbial carbon is that which is tied up in living organisms in the soil, from earthworms to viruses, with fungi, bacteria and nematodes in-between.
These organisms form an essential part of of the soils’ ability to function, but to date assessing how much of the total carbon in the soil is made up of microbial carbon is troublesome as fresh soil samples and toxic chemicals are often required.
Japanese soil science
The situation has now changed, following the development by research workers in Japan of a novel method for estimating microbial biomass using water-extractable organic matter (WEOM) from air-dried samples.
This innovative approach not only simplifies the estimation process but also eliminates the need for toxic solvents typically used in traditional methods.
The work was jointly conducted by Niigata University, Kyushu University, Japan Atomic Energy Agency, and Anhui Academy of Agricultural Sciences, with the findings published in the journal Discover Soil.
50 different samples were examined from ten different profile types from across Japan. These included six forests but just the one pasture.
The aim of the joint research project was to evaluate the relationship between WEOM measurements and the microbial biomass contained in each air-dried soil specimen.
The relationship between the amount of water-extractable organic carbon and microbial biomass carbon obtained from the soils turned out to be particularly strong, though the nitrogen method gave a much less reliable result.
The hope is that this quicker, easier, and cheaper method to differentiate between inert and microbial carbon within the soil will allow a more complete picture can be assembled of the various processes within the soil and how it is responding to methods of management.
One question that this method may be able to address here in Ireland is how the application of slurry affects the microbial fauna and flora in a field. Currently, opinions vary as to the effect of ammonia on subterranean life.
Up until now, the extent of the impact has mainly been guesswork, but this cheaper and more convenient method may allow for a better understanding of the effect of various inputs on the functioning of the soil biomass.
