When you actually look at the carbon cycle model, with all the compartments and flows, you notice that putting carbon into the soil could actually offset all the fossil fuel burning and more. If we did that to the extent that the soil had before we farmed it to death, CO2 movement into the atmosphere would turn negative. Of course, once we got the soil saturated with carbon, it would rise again but maybe no faster than movement from the atmosphere into the ocean would handle.
It's an interesting model because it has very short, short, and long sequestration loops as burning fuel crops, soil carbon coming out over the course of decades, and limestone deposits locking up carbon for epochs, respectively. I suppose all the models are incorrect because they don't include methane clathrates bubbling out of the not-so-permafrost.