Just read an interesting new report about compost. This 19 year study found that compost added carbon at a high rate per year, while cover crops did not. That is in an arid climate, not sure how different it would be for us.
The key point seems to be that carbon can only be sequestered when the nutrient balance is right for the microbes that do the carbon processing.
https://phys.org/news/2019-08-compos...rbon-soil.html