A carbon nanotube production system is used for improving plant growth characteristics for a plant growing medium, for example soil in an agricultural field. The system includes an internal combustion engine, for example a tractor engine, which is arranged to combust a fuel mixture therein which includes a blend of fuels and additives including a carbon nanotube seeding material. The engine is operated in pyrolysis to produce exhaust emissions containing black carbon ultrafine and nano soot, for example by towing an agricultural implement across the agricultural field. At least a portion of the exhaust emissions is captured and conditioned to process the carbon soot into carbon nanotubes. The conditioned exhaust emissions and carbon nanotubes therein are then applied to the plant growing medium, for example by using the agricultural implement to incorporate the conditioned exhaust into the soil.
