In this video, around 10:50 Minutes, Allan Savory claims that:
Now, if it does not decay biologically, it shifts to oxidation, which is a very slow process, and this smothers and kills grasses, leading to a shift to woody vegetation and bare soil, releasing carbon. To prevent that, we have traditionally used fire. But fire also leaves the soil bare, releasing carbon, and worse than that, burning one hectare of grassland gives off more, and more damaging, pollutants than 6,000 cars. And we are burning in Africa, every single year, more than one billion hectares of grasslands...
It is a bit unclear what exactly that sentence means, but I presume (and please correct me if I am wrong) that it means: the amount of CO2 emitted by burning 1 ha of grassland is greater than the amount of CO2 released by 6000 cars in one year.
Is this comparison (or rather, my understanding of it) accurate?