Carbon is notoriously labile, one even might say it is promiscuous. That is, it forms and breaks bonds with other elements constantly. That ability, actually, is why carbon is such a good building block for life.
But it also makes it difficult to isolate and measure very well. Carbon in soil, unless fossilized somehow, is constantly changing: being deposited or exuded by organisms, being metabolized by other organisms, being respired, being oxidized. Thus most carbon tests, like Loss on Ignition (LOI) which heats soil to 550 degrees Celcius (at which most organic matter is incinerated) and measures the amount of mass lost, throw all forms of carbon together and don’t give a very useful number for those of us interested in building stable carbon. Also, they are expensive, require sending soil to a laboratory, and don’t give you immediate results.
An alternative approach is to directly measure the aspects of soil biology that are due to the presence of carbon. Those soil features are “proxies” for carbon. They couldn’t exist without carbon, and become more prominent as the carbon level in the soil increases. Also such tests are inexpensive, can be done on the farm, and can give immediate results.
As a part of its soil carbon program NOFA/Mass has been developing such tests. We have 10 of them now, and have acquired the equipment and materials necessary to do them. Here we give you a quick idea of the tests and what is 2017 NOFA/Mass Carbon Program Soil Test Protocols.