You can consider either www.nori.com of www.indigoag.com.  They both have enrollments although their approach, who owns the SOC that is certified, and pricing is quite different.

As you approach the opportunity of the carbon market, there is a general condition of additivity or additionality.  This represents a marginal shift due to a practice change.

My suggestion is to figure-out what is your carbon inventory as of Jan 2021.  Create a strong baseline in two way: if you are sampling for 2021 season, make certain you include a SOC via certified labs(s).

The SOC inventory process is based on the first 300mm (12 inches) of the topsoil.  The deeper horizon of 300 to 700mm (from one foot to 40 inches) is not in the carbon pool that is in transaction.  The deep soil carbon has a different set of certifiaction.

As you consider all of this, the primary pathway is to sort out your last five or more years in detail to allow the current modeling process to build on your legacy farming system.  

One you have a reasonable estimate of the spatial mapping of SOC then the tweeking of SOC-sequestration zones, aka soil health, strategies can be planned via a Soil Carbon Conservation Plan (SCCP).

Personally, I am an advocate for direct contract SOC sensing and estimation.  In-soil sensors like Veris Technology's iSCAN or AGO's Precision Planting SmartFirmers plus calibration via certified point samples will be used to realign your future carbon plan.   

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