I thought the idea was very interesting, if it could be made to work. I have read several times about people adding carbon to the soil, and increasing fertility, and this seems to follow the same principle.

I think it's the nitrogen oxides in the exhaust, of which there are plenty because of a diesel's high combustion temperature, that is doing the fertilizing, not the carbon. If this is so, this could be a huge breakthrough in reducing fertilizer need. NOx must be finding some way to bind to the soil particles and be converted to usable nitrogen through microbic activity. Somebody should find a grad student who's looking for a dissertation research topic. For small grains (wheat, barley, rye) nitrogen is the primary fertility need. Usually there's enough phosphate and potash in the soil that little of those need to be added. (This is not the case for corn.)

It would be limited to air-seeder seed delivery systems, which have become the standard for small grain farming on the plains. Air seeders are a combination of field cultivator and seed injector. Tillage, planting and fertilizing are done in one pass through the field. Seed is kept in a big hopper, towed behind the cultivator, and is injected through plastic hoses, exiting underground just behind each cultivator shovel. Air seeders are usually 40 to 60 feet wide. They can plant over 40 acres per hour.